Soil FAQ Index
[Prepared by Eric J. Forbis, forb0004@gold.tc.umn.edu, additions by
Bob Jewett, jewett@opus.scs.agilent.com]
Individual entries in the text body are preceeded with a header format
of ### Xy to speed locating the article, where X is section I,II, or III
and y is the letter preceeding the article in the index.
I Soil substrates and mixes
a Soil FAQ intro, substrate descriptions, mixes (Cruder)
b Soil FAQ comments (Verheulpen)
c Soil mixes and seed germination (Verheulpen)
d Sand not recommended in soil mix (Betzler)
e Agrosoak possible zeolite substitute (Brown)
f Soil question observations (Cruder)
g Soil questions and serpentine (Mark)
h Limestone in cactus mix (Boehmke)
i Limestone reply (Bernard)
j Eschew peat! (Peters)
II Hydroponic solutions, substrates and issues
a Hydroponic recipe (Verheulpen)
b Hydroponic recipe comments (Cruder)
c More hydroponic comments (Cruder)
d Hydroponic plant support question (Gustafson)
e More Hydroponic comments questions (Verheulpen)
f Rotting caudex + hydro?/Ariocarpus/Citric acid (Cruder)
III Other growth tips
a Root temperature (Cruder)
b Accelerating growth in cacti (Cruder)
### Ia
From: (Bob Cruder)
Subject: Soil FAQ
Friends:
We probably should start a FAQ on this subject since the soil questions
come up so regularly. Any recommendations interact so much with other
aspects of culture that we could make contradictory but equally correct
observations. I'd like to toss out some generalities, see which ones we
can agree on and start building from there.
Purposes of soil:
The soil mix provides physical support for the plant, acts as a source or
reservoir of water and nutrients, allows circulation of air to the roots
while protecting them from sun damage and desiccation. For some species
it is also important that the soil serve as thermal storage allowing the
plant to survive greater temperature extremes than it could in bare-root
form.
Natural Soil Components:
Most cacti and succulents live in soil with perhaps 3% to 5% organics.
The remainder is mineral and may include particle sizes from clay up to
boulders. Finer soils allow less air circulation and tolerate much less
water before risking root suffocation and rot. Conversely, coarser soils
require more frequent watering to avoid root death due to desiccation.
Desert soils do not experience the cultivation that worms perform in
temperate regions. Neither do they develop thick layers of humus from
which minerals and humic acids leach with each rain. Rapid surface drying
slows the breakdown of plant residues. In the Sonoran desert, carpenter
ants may be the major force for removal of surface residues. In Africa,
it is the termite. The major source of soil organics does not come from
above. It is the roots of prior plant generations.
Except for plants with seeds that must be deposited by flowing water like
the river paloverde, plants do not choose their soil. They try to survive
where they are. The soil in which they naturally survive may not be
optimal and may just be too poor to support any competitors. Not
surprisingly, there are perfect soils in which practically any plant will
do well. Such soils are so rare in nature that no species would evolve to
depend on them and no collector would perceive them as the native soil
for any particular species. Nonetheless, we can produce such soils
artificially.
Available Natural Components:
Clay particles array themselves in a fashion that stores water and
nutrients and in natural soils prevents both from sinking below the root
zone. They also pack so tightly that root aeration is compromised. As
much as 10% clay in the form of kitty litter may save mixes that would
have been too friable to hold plants upright. Clay makes the mix stick
together but must be used in moderation.
Fine sand/silt in natural soil holds moisture in narrow interparticle
spaces and wicks moisture into the root zone from the subsoil. This
service is not needed for potted plants. The particles pack too tight for
good root aeration and offer little ion exchange capability. They also do
little to support plants structurally. There is no specific need for sand
in a soil mix.
Natural gravels and pebbles improve air circulation but do not hold water
or nutrients. They are often so rounded that plants potted in pure gravel
just tip themselves out of the pot. Sometimes a little clay will hold the
mix together but pebbles are best used as a top or bottom dressing or as
the starter medium for aero-hydroponic systems.
Those who want to screen their own should discard particles under 1 mm
which would pass through the typical kitchen strainer. The 2mm to 5mm
particles which pass through 1/4" hardware cloth are useful for soil
mixes. The 5mm to 10mm pebbles which pass through 1/2' hardware cloth are
best for hydroponic use or as top dressing for large plants.
Granular diatomaceous earth looks like kitty litter and has particle
sizes from 1mm to 4 mm. It absorbs water in its pores and supports ion
exchange. It is sold as a mechanic's oil absorbent and would be a perfect
medium if it were available in coarser form. It is a great top-dressing
because it does not stick together and the surface quickly dries to
eggshell color. Even without much cohesion, its weight and wet-ability
provide good plant support.
Crushed pumice shares the same characteristics and is available in
coarser sizes. It is not cheaply available in most areas in less than
boxcar-sized loads but is the product of choice when available.
Crushed basaltic lava rock has larger vesicles and lower silica content.
The particles cut into each other providing better physical plant support
than any other medium. Lava rock is slightly soluble. Minerals leach out
making the soil more alkaline and it breaks down into smaller particles
over time. A high proportion of lava rock will cause the same problems as
will sand after enough leaching.
Peat moss is the decomposed remains of temperate bog mosses. Its fine
particle size requires moderation to avoid root suffocation. It releases
humic acids which may combat some root pathogens but in breaking down it
competes with the roots for available oxygen. As a primary component it
resists re-wetting after drying but in proportions less than 25% and when
ground with the other components through 1/4" hardware cloth re-wetting
is not a problem.
Peat moss stores water and nutrients well while providing little of its
own. It helps in physical support by holding the soil together but relies
on fine roots and fungi to assist in that task.
Peat moss is a thermal insulator and prevents plants from transferring
heat to or from the soil. Plants potted in peat moss will have lower heat
and cold resistance.
Peat moss lowers the PH of soil and is useful to compensate for lava
rock. Otherwise, one to three tablespoons of lime must be added per cubic
foot of peat moss to avoid excess acidity. Dolomitic lime is preferred to
avoid an excess of calcium compared to magnesium. Peat moss is mined from
environmentally sensitive areas with limited regenerative capacity. Many
avoid it for that reason and use the alternatives described below.
Artificial Soil Components:
Vermiculite is an expanded form of mica. It holds water and minerals well
between its layers. It tends to shrink when wet and expand when dry and
moves a lot when watered. The volume changes can be compensated by about
one gram of polyacrylamide crystals per liter. As with lava rock, the
particles break down over time. Since the surface of vermiculite dries
too fast for exposed seedlings while the depths offer too little air
circulation for most plants, it should be used sparingly, no more than
25% of the mix.
Rock wool is derived from a mixture of ground stone which is melted, spun
and compacted. It holds water and minerals well but slowly releases
alkali like lava rock. Its fine pore size may suffocate roots except
where the smallest cubes of rock-wool are used for seedlings. In
hydroponic use, larger plants are allowed to arrange their roots on the
surface of a rock-wool slab while plant support is provided from above.
Bulk rock wool looks like grey cotton and can be used in soil mixes. The
chunks do tend to stick together and aggregate. Breaking them down
through a 1/4" mesh screen embeds a multitude of fine fibers in one's
skin. There are many better alternatives to rock-wool in a mix.
Perlite is an expanded silica. It is slightly porous, offering some water
and mineral storage capacity. It provides good plant support when wet or
dry but tends to suspend itself during watering. It will let a plant fall
over but will stiffen up when the water drains out. It will also float up
through a top-dressing. The main value of perlite is its support for air
circulation while also distributing water well through surface wicking.
Many plants grow well in straight perlite with hydroponic feeding. A pot
or tub of perlite can water itself via a fiber wick extending into a
vessel of hydroponic solution. Perlite is an excellent bottom dressing to
prevent potted plants from wicking up too much moisture from drainage
saucers. Some sources of perlite have high alkali content, mostly
potassium and will raise soil PH over time.
There is also a styrofoam product called styromull with characteristics
similar to perlite. Some European experts recommend it but it does not
appear to be available in the Americas.
The three products described above are thermal insulators having the same
limitation described for peat moss.
Baked clay spheres or extrusions which are collectively called grow-rocks
in the hydroponic trade provide drainage and air circulation and store
significant amounts of moisture and minerals. They are too coarse to use
in other than hydroponic systems and most are too smooth to provide good
plant support. A variant made of expanded shale avoids those limitations
and is the equal to pumice. These products are of little value in low
concentrations, becoming expensive pebbles and are too expensive to use
in quantity unless one has a local manufacturer. As with the natural
mineral products, shipping costs far exceed the initial cost of the
material.
As an alternative to peat moss, one can use mixed compost or composted
bark chips. Mixed compost may contain manure, fallen leaves, grass
clippings, agricultural residue, recycled newspaper and/or sawmill
residue. Most are well composted and can be used like peat moss but
without the re-wetting problem.
One superior product called "America's Choice" was long-fiber sawmill
residue. The long fibers provided plant support but were coarse enough to
avoid packing down and suffocating roots. Alas, Wal-Mart no longer offers
it. Perhaps some of the list members can find alternate sources.
Bark chips have a much lower surface to volume ratio. They offer good
drainage and can be used in high concentrations without suffocating
roots. They do not offer good support and slide over each other easily
but are much less likely to float up than perlite. Eastern sources of
bark have predominantly 1cm and larger particle sizes while western
sources are below 1 cm. One can screen it and use the same particle sizes
as were recommended for gravel. Bark is not fully composted. It releases
humic acids slowly so that little lime is needed to regulate PH but it
can absorb significant amounts of nitrogen from the soil mix during its
initial breakdown. One can add a tablespoon of dolomite per cubic foot
and 2% to 3% by dry weight of nitrogen in some soluble form to a dampened
mix and let it re-compost a few weeks before use.
Favorite Mixes (FLAME BAIT):
My favorite mix for aero-hydroponic use is equal parts of pea gravel and
bark chips which will pass through 1/2" hardware cloth but not 1/4"
hardware cloth.
My current favorite mix for daily watering with hydroponic solution is
equal parts of granular diatomaceous earth, perlite and screened bark
chips. All pass through 1/4" hardware cloth but not through a 1mm screen.
My favorite mix for gift plants which will be watered irregularly with
our local alkaline water contains equal parts of peat moss, vermiculite,
perlite and granular diatomaceous earth with 1/2 tsp of polyacrylamide
crystals, one tablespoon of Osmocote pellets and two tablespoons of bone
meal per gallon of mix. The mix goes through 1/4" hardware cloth just to
break up the lumps.
The Future:
Please post your opinions if you disagree with any of the above. Describe
any products that you use which are not included. Also post your favorite
mixes which will be used to adjust the recommended ranges for ingredients
and combined into a recommendation which allows for locally available
alternative ingredients.
Bob Cruder - bcruder@miaco.com
### Ib
From: waverheu@vub.ac.be (Verheulpen W.)
Subject: soil faq : some comments
Thanks to Bob for the initiative of putting together a faq
on the properties/components of substrates. He is a brave
man indeed :-)
:-) However I have a few comments open for discussion.
These are probably due to other sources for the discussed
materials & the relevancy of the comments highly depend on
how much "non USA" the faq is supposed to be :-)
Maybe they're also given by the advantage of living in a small
country: more material is available on a small surface :-)
>Most cacti and succulents live in soil with perhaps 3% to 5% organics.
I would not put forward a figure here. Many S american
genera thrive in habitats that contain much more organics
than suggested here, just to name Gymno, Notocactus &
Parodia.
> Clay
There are a multitude of "clay-like" soils. One has to avoid the
pure/fine alluvial deposits of the material. We know of
several spots where coarse clay was deposited which has
almost no packing properties. One of our countrysides here
is having a very coarse clay where sugar beet is grown it
is the material "par excelence" unfortunately it is a major
source of nematode infestation :-) It is not the idea of
making the geological survey of clay here but the way it is put
seems too restrictive to me.
>Sand
A lot of people over here use sand in their mixes. It is the simplest
way to improve drainage. We have choices available : from
the yellow type builders sand over gravel like sands on to
pure quartzite sands (used to polish cement floors over
here) Although I agree that the material can be totally
inert it is a good weight compensation for those that want
to grow in pure peat-like soils & enhance drainage.
>Peat moss
Ha ... The name covers a tremendeous variety of "peat-like"
materials over here. They range from sphagnum (the very fine
fibered old peat, that used to be imported from russia!)
over the coarse garden-peat to the black-moor peat that is a
trademarket of all flower growers in Holland. It has become
the replacement of the (high qualified) leaf-mould for bulk
growing due to the fact that it can be "mined" & does not
require a lengthy compostation. it is also readily available
for the home grower.
Only the "red" peat has a significant pH lowering capacity.
The black varieties are almost inert in this respect.
All the peats on the market here do NOT store nutrients well!
They are washed out by watering. They all come "pre-manured"
& depending on the plant & pot size in sufficient quantity
to provide "food" for 3-6 months.
It can be used to compensate for alkalinity of lava
additions but IMHO it remains to be seen if such composition
(peat + lava) is a good growing substrate due to the
continuous chemical instability & based on some lab
experiments I would not reccomend this combination even not
after a lengthy "rest" period
>Vermiculite
Experiences here show that it collapses after drying with NO
regain or regeneration of form, forming a layer of mica
pellets shuting off the soil in a most dreadfull way
>Perlite
We used to have intensive algae growth on perlite when
exposed to direct sunlight
>Styromull
Do not worry Bob, I know it is there but I've never seen it
on the market in Europe either :-)
>Baked clay spheres
Well over here that is a chapter on it's own. Many many people
use them over here. They are available in all granulates
from 0cm to ...cm. I use the 3mm variant for a number of
applications. They can easily be grinded in an old coffee
mill :-) & broken down to whatever size you grind them.
Sifting out the powdered component leaves you with a
sintered/baked high mineral high porosity component which is
a great additive. One has to make sure that one buys the
hydroponic quality. The building type is often manufactured
from low quality clays with very high calcium contents & put
into water may quickly make the pH raise to 9 & above :-)
The hydro one is almost neutral to slightly alkaline (pH 7.2
7.3)
So far the comments
Why would you consider yr favourite mixes as flame bait ??
I always claim that one should experiment to find the
substrate that seems to make the plants grow at their best
in your particular environment. As this environment is
substantially different 4 U & for me I expect that our
substrates would be different to the same extent + flavoured
with some personal touches ... so ...
My personal soil "pet" :
I have been experimenting for many years with crushed brick
&/or clay pot debris. I break them down to suitable pieces a
leave them weathering out in the garden. Now that makes a
material of choice :-)
The "old" gravel that was used on to tennis courts also
makes a great additive, & what to say about the modern sisal
fibres that start to be marketed as a replacement of peat?
& I'm sure I'm still forgetting things :-)
Sure hope guys/girls that I did not knock you off yr socks
with this. I told you I'm a freak didn't I :-)
Willy
### Ic
From: waverheu@vub.ac.be (Willy A Verheulpen)
Subject: Re: Soil for germination of cacti
>Massimo De Sanctis says
>Hi guy there.
>
>I have about 30% germinating success whenn sowing cactus seed. After
>many years and many seeds thorwn away, I am getting convinced
>that using a soilless media is definetely a plus.
>
[more deleted]
I can not give you an explicit answer to yr question but maybe let me
offer some possible advice :-)
I have been sowing numerous things over the last 20 years & I also
started to believe that "soilless" was the solution. In my opinion it is
NOT, not more than the belief that soil should be sterilised before
use.
I have come to some experimental setups that give me a very good
yield in germination but after that one is always ending up in some
twilight zone of more/less uncontrolable success.
Now I am making a soil mix with up to 60% mineral material. I have had the
best results with "crushed brick" like material probably because of its
capillary capacities. From this material I am sieving out the dust fine
stuff using a "flour sift". The 40% remaining I make up with leaf mould,
some peat, some garden clay. (I suppose that bark would be worth
testing but that is hard to find here in quantities smaller than a truck
load :-) )
To the final mix I add 10-20% of charcoal. I make sure that the max
granulate diam is not more than 1.5 mm.
My common mistake was to mix ingredients the day before using the
mixture for sowing :-) Now I make it well in advance, that is November
or so to be used in Feb/Mar next year. I make more than needed,
can be easily recycled into your normal potting soils.
I never keep it for several years. Imake a new batch every year.
I keep the mixture in a styrofoam container with lid, so it is in the dark
& I make sure that it is kept moist & more/less warm say 17/20 deg cent.
This will balance the mixture & if some fungus grows now then you are lucky
it will show you that the mix contained something harmfull & at least it
declared itself before the seeds where put in :-)
If you do not trust the quality of what you mixed up, then make a few
sowing tests. Make sure you get seeds harvested from your own plants.
(Or from plants of some nearby cactophile :-) )
Do not care if the are hybrids, you only want to see them germinate +
observe the behaviour during 1-2 weeks. It will learn you how good the mix
is. You must not be afraid of fertlising. (See about hydroponics!!) to improve
growing. Everything you gain in growth before the winter season is a plus!
At last one important thing : YOU MUST USE A FUNGICIDE ON THE
SEEDS. Use the "dry" approach the way it was explained here on the forum.
Maybe you do not like to do this, I do not like it either but if you do not
want to get broke on seed bills after a number of years ending up with
almost no plants yields then reconsider :-)
I know that for many species good results can be obtained by a strict sowing
drill. I have noticed many times that a "quicky" sowing in June/July because
seeds came in too late never yields a satisfying result. It is crappy & will
remain so (left in some room 4 exceptions :-) )
To boost your moral : I have sown tiny Parodia seeds with 100% germination
& maybe 90-98% recovery after the first pricking out in the next year. Yet
everyone claims that raising Parodia from the tiny seeds is a pain. It's NOT
provided the best approach technique. HOWEVER ! the seed was from
local harvest & ripened in the best conditions!
Do not trust too much the commercial sources ... :-)
Hope this helps
Willy
### Id
From: JABetzler@aol.com
Subject: Re: using sand in mixes - not
Most C&S growers here in southern California use no sand in their mixes. Few
use dirt from the ground. Many people use media that is made up or humus or
bark, peat moss, a loose filler that has lots of air in it and miscellaneous
stuff. I worked at Grigsby Cactus Gardens for a few years and formulated this
mix for myself from the ideas gleaned there and my experience over the last
decade or so:
1 part Unigrow potting soil
1 part Supersoil
2 parts Pumice
Occasionally I add a bit of charcoal if I can get it and I have experimented
with Diatomaceous Earth (DE). If pumice is not available then pearlite or
even vermiculite can be used. Pumice is great because it does not float as
easy as pearlite. It also has a cation exchange capacity that releases water
and fertilizer over a period of time rather that all at once. I also add
Osmacote when I actually use the soil. The one quality that these soilless
mixtures have over a soil based mixture it that they drain fast. The water
poured into the pot drains through in a mater of seconds. The mix is wet in
the pot but the water does not stand there.
Others may have formulations that are different, I would like to here from
those that use soil. There are commercial Cactus Mixes available as well
and I have used those in the past.
Good Luck - Joey Betzler 1994/08/20/0805 PST
### Ie
From: rbrown@ctsnet.cts.com (J. Reese Brown)
Subject: Re: More soil remarks...
>Mark at SPNOVA@aol.com wrote:
>..........
>Something I happened upon a couple years back was Zeolite. At first I was
>interested in just using it for top dressing, as the stuff is so crystalline
>& pretty, and (at least in Oregon) plentiful. The plants that got dressed
>with the stuff immediately perked up and started developing better spination.
>Started making a special mix with it for Discocacti & Melocacti & some other
>mineral-loving south-american species, and have had 100% success with it.
>So what's Zeolite? It used to be mined (probably still is) for use in
>water-softeners. Zeolite is a combination of minerals formed from intense
>heat and pressure in and around volcanic activity. It is very crystalline,
>and has a property similar to pumice, in that it will retain moisture without
>being 'wet'. One of the calcite-type minerals seems to attract roots, and
>I've found small feeders growing right into the crystals. Wish I had more
>info, so if anyone out there knows more about the Columbia River Zeolites, I
>would welcome more information.
>Another 'additive' I've been fooling around with is the addition of
>Serpentine for certain alpine succulents (Lewisias, Claytonias, Talinums, and
>the like). At Rare Plant Research, Burl and I have spent a bit of time
>theorizing about the relationships between specific plants and their
>habitats, and he's been experimenting with the Serpentine soil theory. A lot
>of work to be done on all of this stuff, looking forward to see what pans
>out!
Have any of you ever experimented with using the water retaining jel
material. It is sold under a variety of names but one commercial version is
"Agrosoke". It is a crysteline looking powder bur when put into water, it
absorbs about 20X its weight in water and swells up. It is used extensively
by the growers of tropical plants. It seems like it might have some benefit
to us in providing an extended source of water without making things soggy.
It might work in ways similar to Zeolite.
Reese Brown
### If
From: (Bob Cruder)
Subject: Soil Questions
Please allow me to comment on some of the recent statements and questions
on soil components. I'm not sure that my earlier posting used terms with
which everyone agrees and would appreciate further feedback.
1. Willy has questioned my statement that most C&S live in soil with 3%
to 5% organics. That was my recollection from an Arizona Sonoran Desert
Museum article some years ago. Since most of their research was done in
the Sonoran, Mojave and Chihuahuan deserts, their results may be somewhat
biased but so would statements based on epiphytic species whose "soil" is
100% organic detritus.
Soil in southern Arizona and in west Texas which I've been able to sample
is well under 1% organics. All percentages are by dry weights. Even a
dense organic like bark chips is much less dense than mineral materials
like pea gravel. The 3% to 5% may mean 30% to 50% on a volumetric basis.
Higher volumetric proportions than that are seen in bogs and on forest
floor but are not particularly common worldwide.
2. Willy also questions the term "clay". In geological usage here, true
clays are colloidal in size and will take hours or days to settle from
suspension. Above that in size are silts, sands, gravels, cobbles and
boulders. A chemist would define a clay based on molecular/crystalline
structure and would call the massive zeolite rock deposits clays just as
well as the slippery stuff used for pottery.
What writings I've seen on soil composition use the geological
interpretation. In the presence of sufficient calcium ions, the colloidal
clays flocculate into silt-sized particles but the transition can be
reversed by adding enough sodium ions to displace the calcium. The
"natural" particle size drives the usage.
3. There does seem to be some question regarding the particle size of
sand. Common usage here is to call particles more than about 1mm in
diameter a fine gravel. The sands constituting most of my local soil are
under 0.2mm diameter. I found them able to suffocate roots even without
the addition of organic material. That is probably not the particle size
which Willy has used "to grow in pure peat-like soils and enhance
drainage". What usage would readers prefer?
4. Spagnum peat is commonly available here and the term peat moss is used
interchangeably with it. The hyphinum peat (spelling ?) is rarely even
seen except for the Hyponex brand and is also called black peat. It has
extremely small fiber size and is almost guaranteed to suffocate roots.
That is probably equivalent to what Willy calls "black-moor peat". We
seldom see the term "leaf-mould" used anymore because that product was
originally mined from temperate forests and is no longer available.
Artificial composts may contain leaves but usually contain many other
organic materials as well. They can only be described as compost or with
a trade name. Would the terms "spagnum peat", "black peat" and "compost"
satisfy readers?
5. I claimed that peat moss had the ability to store nutrients and Willy
disagrees. More properly, the porous fibers have an ion exchange capacity
as do clays. The ability to store and release limited amounts of ionic
nutrients avoids both toxic levels and deficiencies in the face of
variable delivery and consumption. I did not intend to imply that they
would retain nutrients sufficient for weeks or months of growth. Would
readers prefer that I use the more formal term "ion exchange capacity"?
6. The coarse vermiculite that I use compacts in response to the surface
tension of absorbed water but does seem to expand when the water dries
out. After drying, a light breeze blows vermiculite out of my pots. I
have ceased to use the fine grade with particle sizes under 0.5 mm. Like
the vesicular basalt sold as lava rock, vermiculite slowly breaks down
into smaller particles. The fine grade turns clay-like so quickly that it
is unsafe to use. This sounds like what Willy has encountered. What
experiences have other readers had?
7. I've never seen algal growth on perlite in plants that I have grown
but see it often in potted plants from greenhouses. Can anyone advise
regarding the level of relative humidity required? The tendency for
perlite to float after watering requires that a thick top-dressing be
used for cosmetic reasons. Are any readers using perlite without a
top-dressing?
8. Willy has access to a greater variety of baked-clay products than I do
in Colorado. All that I see on display are the approx 1 cm spheres but
have seen advertisments for the 2 mm to 3mm diameter extruded products.
I'd appreciate some input from other readers. This may well be a perfect
material but the FAQ needs to reflect some common availability.
9. Mark has mentioned both the Zeolite and serpentine. The coincidence of
asbestos with serpentine rock poses a respiratory danger that would
concern OSHA and perhaps the EPA here. The California EPA closed an ORV
park a few years back because the density of airborne asbestos kicked up
from the serpentine surface rock exceeded legal limits. Significant
distribution or use of serpentines in a business setting could expose one
to civil and possibly criminal penalties.
The Zeolite is much more interesting. After reading Mark's post, I called
some local water softener companies and found that they used ion-exchange
resin beads called "dialite". I'd like to find out what softener
distributors might still provide a source of Zeolite.
10. Reese has asked about water-retaining gel crystals sold under the
trade name "Agrosoke". This material with the generic term granular
polyacrylamide gel is commonly available in two forms under a variety of
trade names. One form absorbs 200 to 400 times its volume in water but is
decomposed by UV when exposed at the soil surface and ceases to absorb
when exposed to sufficient levels of salt or other ionic solutes.
I add it to my cactus mix to support moisture-loving plants like zygos,
bromeliads and african violets. It was once sold to remove the wave
action from water beds by gelling the water. If you made the bed too
stiff or if you wanted to drain it, you just added salt.
The other form absorbs only 50 to 100 times its volume in water but is UV
stable and is less sensitive to salt levels. It is better for plants that
are difficult or impossible to repot because of their size or spination.
A pot filled with gelled crystals drains well but has almost no air space
and can suffocate roots. It might work as a medium for top-feed
hydroponics where oxygenated solution is continuously supplied. I've had
no problems when the gelled volume comprises up to 25% of the total soil
volume but start to get anoxic areas with higher proportions.
Bob Cruder - bcruder@miaco.com
### Ig
From: SPNOVA@aol.com
Subject: Re:Soil Questions&apology
Bob Cruder recently wrote:
>9. Mark has mentioned both the Zeolite and serpentine.The >coincidence of
asbestos with serpentine rock poses a respiratory >danger that would concern
OSHA and perhaps the EPA here. The >California EPA closed an ORV park a few
years back because the >density of airborne asbestos kicked up from the
serpentine surface >rock exceeded legal limits. Significant distribution or
use of >serpentines in a business setting could expose one to civil and
>possibly criminal penalties.
First off, I must assure readers that the perceived threat of exposure to
asbestos from serpentine rock within the context of what I previously
described, strikes me as rather unlikely, but one should be aware that the
serpentines do contain varying amounts of asbestos. At Rare Plant Research,
there are always a number of on-going experimental techniques in progress,
and presence of serpentine soils in the experimental areas in no way effects,
or ever comes into contact with sale plants.
It does, however, seem odd to me that the Berkely Botanical gardens would be
investing so much in the construction of a "Serpentine-soils" garden, what
with all that dust floating around in the course of construction & the
general public. They've certainly hauled in more than ten or twelve square
yards of the stuff, to make their beds... I wonder whether they are aware of
these potential penalties and health-risks Bob speaks of. Strikes me as a bit
intangible, but not impossible. A good point raised that I was negligent in
mentioning, my apologies to the group.
Mark
### Ih
From: "Boehmke, Jim"
Subject: Limestone in Cactus Mix
For some cacti it is normally recommened that when the seedlings are
transplanted for the first time that the soil should have a basic pH and in
order to achieve this it is suggested to add limestone to the mix.
Can one dig up limestone bearing soil and or gravel in the desert areas where
cacti are known to grow in limestone rock and soil and use this in some way?
Should a commercial product be used? If so, what product should be used.?
How much limestone, in what ever form, should be added to your regular cactus
mix?
Jim Boehmke
### Ii
From: Richard Bernard
Subject: Limestone in Cactus Mix
Responding to msg by JCBOEHM@saix367.sandia.gov ("Boehmke,
Jim") on Mon, 26 Sep 11:10 PM
Dear Jim,
Yes, cactus found growing in limestone, such as the
ones in the Trans-Pecos area of Texas, benefit from the
addition of such in the planting mix. I find dolomite effective
for this purpose. It can be purchased readily at a nursury or a
aquarium store.
Richard Bernard
### Ij
Eschew Peat!
From: Ralph R. Peters, 3 May 1996
My dictionary defines "eschew" as "to avoid habitually especially on
moral or practical grounds; SHUN" and I think that sums up my attitude
on the use of peat in potting-soil mixes. In my opinion, plants that
are generally considered "easy" to grow (e.g., Mammillarias, Rebutias,
Lobivias, and Echinopsis) are easy because they tolerate peat-based
potting-soil mixes, while plants that are considered "difficult" (e.g.,
Ariocarpus, Sclerocactus, Pediocactus, and Echinomastus) are difficult
because (mostly) they don't tolerate peat-based potting-soil mixes.
One can grow "difficult" plants in a peat-based potting-soil mix
("difficult" not "impossible") but one has to be very careful or the
plant losses will be total rather than terrible.
I live in Albuquerque, NM and became interested in growing local cacti
and succulents about 15 years ago. I am especially interested in
Pediocacti, Sclerocacti, and Toumeyas which have a reputation of being
difficult. It would seem that growing them should be easy for me; that
was not the case for my first 10 years! During that time, I grew the
plants in a peat-based potting-soil mix (~two-thirds coarse sand, ~
one-third Metromedia 360 potting-soil which is great for geraniums and
such) and discovered that after about 2 years in a pot the plants
started to lose their roots and die from what I affectionately term the
"orange rot". I tried everything! I tried all sorts of recipes for my
potting soil. I carefully monitored the soil moisture. I used
dangerous chemicals as soil drenches (bad side-affects!). I repotted
often trying all sort of things with the unhealthy roots (dip in
chinosol, cut,...); but then many of the plants died immediately after
repotting. Watching a 6 year-old, blooming-size Sclero mesae-verde
dissolve into orange-mush is not a happy sight!
It seemed that the potting mix might be the problem. I (brilliantly!)
noticed that plants in habitat never grow in peat and are quite happy to
stay in one place for many years!! Discussions with Steve Brack at Mesa
Gardens (> 100,000 cacti and succulent plants are currently flourishing
there) convinced me that peat MIGHT be the problem. His suggestion was
to try the totally radical concept of growing them in a much more
natural potting-soil mix containing local soil, sand, and pumice.
To test the hypothesis that peat was the problem I ran a number of tests
growing the same or similar plants in a peat-based mix and a native-soil
mix. The results were uniformly and stikingly similar; after a few
years, plants grown in peat-based mixes became sickly while those grown
in the native-soil mix remained healthy. For example, I planted about
40 pots of seed of Pedios, Scleros, and Toumeyas in both the peat-based
mix and the native-soil mix. The seeds germinated equally well in both
mixes (after winter stratification) resulting in more than 300
seedlings. During their first year of life, I could see little
difference between plants in the two mixes. During the second year,
plants in the peat-based mix grew more slowly and their death rate was
higher. I repotted all of them in the spring of the third year and
discovered that the roots of plants grown in the peat-mix were sickly
and that in many pots more than half the plants had orange-rot in their
roots. Repotting these plants was a mess with a significant time taken
in plant surgery. The plants grown in the native-soil mix were
uniformly healthy and no cases of orange-rot were observed. Easy plants
flourish in this mix also; my Haworthias are "pot-eating" monsters!
The particular mix that I use works well for me, but may not be
appropriate for others with a significantly different climate. I list
it below only as an example.
63 % coarse sand (.1 - 1 mm diameter)
25 % soil (mine is a fine aeolian soil from a
location that has knee-high native grass during
the summer monsoon season)
12 % white agricultural pumice
Other "native-soil mix" growers in NM use a wide variety of mixes
ranging from pure decomposed-granite "soils" gathered near the base of
the Sandia Mountains to mixes that are mostly fine mesa soil mixed with
a little sand.
My suggestion to growers is to EXPERIMENT! Mix up a couple batches of
potting-mix that contains no peat and are low in organic content. Those
from the rich prairies of the American Midwest might try a mix with a
small amount of soil and lots of coarse gravel, pumice, and other
inorganic materials that promote drainage. Then pot up a few plants
that you can afford to lose. (That common Mammillaria on the back shelf
that hasn't been repotted in 6 years is a good candidate!) Keep track
of the results! Adjust the mix! With a little experimentation, you
will find a mix that allows you to be more successful with both
difficult and easy plants.
Good luck and good growing!!
Ralph R. Peters - rrpeter@isrc.sandia.gov, added 3 May 1996
### IIa
From: waverheu@vub.ac.be (Willy A Verheulpen)
Subject: hydroponics recipe
Here goes the recipe that I got from one of my friends.
He has a 400+ sq mtr greenhouse with the most wonderfull plants
& he uses this "mix" to water his plants
The article states that it works best in soil with a low calcium content
because of the SO4 precipitation(s)
quantities in grams !!
Solutions A & B made up separately to avoid precipitation of components!
Solution A
-----------
Iron II sulfate FeSO4 8.5 gr
Maganese sulfate MnSO4 3.5 gr
Boric Acid H3BO3 5.0 gr
Zinc sulfate ZnSO4 0.35 gr
Copper sulfate CuSO4 0.35 gr
Chromium chloride CrCl2 0.35 gr
Nikkel sulfate NiSO4 0.20 gr
Cobalt sulfate CoSO4 0.20 gr
Aluminum sulfate Al2(SO4)3 2.0 gr
Potassium bisulfate KHSO4 10.0 gr
aqua dist. pro 500 ml
Solution B
----------
Potassium bromide KBr 0.2 gr
Potassium Iodide KI 0.2 gr
Ammonium silicofluarate (NH4)2SiF6 0.4 gr
Ammonium vanadate NH4VO3 0.2 gr
Ammonium molybdate (NH4)6Mo7O24 0.2 gr
aqua dist. pro 500 ml
Final buffer solution
--------------------
Sodium chloride NaCl 2.0 gr
Potassium nitrate KNO3 12.0 gr
Magnesium sulfate MgSO4 2.0 gr
Ammonium nitrate NH4NO3 20.0 gr
KH2PO4 150.0 gr
K2HPO4 50.0 gr
aqua dist. pro 1000ml
Stir this solution until components are fully dissolved, then add while
still stirring : 5 ml of solution A
5 ml of solution B
>From this final solution one can add 3 to 5 ml per liter water depending on
the initial alkalinity of the water. The pH should be between 6.0 & 6.5
when this buffer solution is used.
I would very much welcome any comments !! Bob ?
### IIb
From: (Bob Cruder)
Subject: Hydroponic Mix
Willy asked for comments regarding the hydroponic formula that he posted.
It is similar to a number of general purpose mixes that I have seen but
may benefit from some recent research.
1. A quick calculation of total solute content shows that solution A
contributes about 300 ppm and the buffer solution contributes 700-1000
ppm. Fast growing leafy plants growing in a fast-draining medium like
pearlite or gravel with regular circulation of the solution can make use
of a 1000 ppm and up solution. Slow-growing plants can't make use of that
much solute and slow-draining media can often allow localized
concentrations 2-3 times that of the feed solution. Many growers have
reported root tip burning above 1500 ppm.
2. Some of the trace minerals in solution A are well above current
practice. For example, the boric acid accounts for 50 ppm. The usual
practice is 5 ppm to get 1 ppm of elemental boron.
3. I've seen no references for aluminum as an essential mineral and
several relating to its toxicity and ability to bind essential minerals
into insoluble complexes. I would recommend deleting the aluminum
sulfate.
4. The ammonium silicofluorate is a good idea. Many xerophytes and
halophytes have a requirement for silicon. Silicates slowly dissolve in
alkaline solution but not in acid and the silicate present in one's tap
water may be precipitated when one adjusts the final PH. Users of
rockwool growing media can eliminate this ingredient because the medium
leaches silicate as well as slowly raising the PH of the solution.
5. Ammonium ion is used as one component of available nitrate. Some
plants can use it and others find it toxic. The editors of Practical
Hydroponics recommended that nitrate from ammonia be no more than 3% of
the available nitrogen for the more sensitive plants. To achieve PH
balance without excess ppm of other anions requires that nitrate be the
negative ionic component of most or all of the other ingredients.
6. The buffer solution is the primary source of both nitrate and
phosphate and is rather heavy on the phosphate. While phosphate ion is a
good buffer to resist PH fluctuations, it can bind some of the anions
into insoluble complexes and often encourages more root growth than
hydroponic culture really needs. I've seen recent moves to reduce
phosphate ion levels for this reason.
7. Although the solution would be less stable against PH variation, the
use of sulfate ion as the primary buffer and nitric acid as the acidifier
would speak to both item 6 and 7. Note that roots replace all absorbed
anions with hydrogen ion an all cations with hydroxide ion so the PH will
always have to be checked and adjusted depending on just what nutrients
are being absorbed most rapidly.
8. Some minerals don't stay in solution well, tending to form complexes
which are not bioavailable. This applies to all of the transition metals
including iron. Commercial mixes use chelating agents such as disodium
EDTA to prevent the occurrence. Lacking this, one needs much higher
levels of those anions. This may explain the high ppm from solution A.
As readers have probably already concluded, it is not easy to make one's
own solutions especially given the rate of change of knowledge, the need
for tiny amounts of pure chemicals which are often sold with a 500 gr
minimum quantity and the need for meticulous weighing and mixing to avoid
variation in the final product.
Where available, the prepared mixes are easier, safer and cheaper. An $8
jar of General Hydroponics Floragro is about 1 lb. At 1/4 tsp or 1 gram
per gallon, the smallest jar makes 450 gallons of solution. I use 2-3
gallons per day and the twice/yearly cost for the jar is a small price to
pay for the convenience of mixing.
I now premix the Floragro powder with my citric and malic acids for PH
correction and (in summer) Miracid for additional nitrogen and a dilutent
so that the resulting powder mixes at exactly 1/2 tsp per gallon.
Bob Cruder - bcruder@miaco.com
### IIc
From: (Bob Cruder)
Subject: More Hydro Questions/Reply
Thanks to Willy's interest, I can use more of your bandwidth to
prosletize on hydroponics.
1. On a raft hydroponic system, one normally makes a hole larger than the
plant stem and wedges the plant in with a non-rotting fiber like
fiberglass. One could just make the hole smaller and wedge the plant in
and indeed that is just what I did with my lithops. The problem is that
styrofoam is not sufficiently yielding to allow for growth. The lithops
will just wedge itself upwards and an ariocarpus would probably do the
same. Plants with more cylindrical trunks might be girdled by the
pressure.
2. So far, the use of an airstone has not generated rot problems from the
overspray. There are two reasons for this. First, my relative humidity is
so low that a typical droplet (.1 mm) dries within minutes. The
detergents present in the commercial hydroponic mix encourage the droplet
to spread which makes it evaporate faster. The second reason is that I
clean the tank weekly, refilling it with bacteria-free solution and
adding 5 drops of bleach per gallon of solution.
3. I do use opaque vessels to decrease algal infestation. Some will
always grow around the edge of the styrofoam but I just wipe it off
during the weekly cleaning. Since the bleach slows the algal growth rate,
a rapid increase in algae would indicate that some other organic material
is reacting and consuming the bleach. BTW I have not found any foam which
tolerates the UV at >6400'. The top surface will slowly powder. I replace
the foam annually with cacti but hope for longer term use with leafy
plants which shade the foam better. By the time that I replace the foam,
every pore in the foam has resident algae.
4. Roots grown in hydroponic environments do differ from those grown in
soil. Some plants grow roots based on need and in the direction of
moisture. In hydroponics, such plants grow small root systems that wind
around themselves. Other plants grow roots based on a structural plan.
Those roots are about the same size and shape as soil grown ones.
Hydroponic roots do usually have fewer root hairs. There are two reasons.
First, fewer are needed. Second, the high oxygen requirements of the
hairs may only be properly supplied on the outside of the root mass. In
soil, root hairs grow and die off all the time. In hydroculture, a more
continuous equilibrium level is maintained. This is not really a problem
with cacti and succulents which are often de-rooted when transplanting
just to avoid transport of pathogens. Most specimens would not really be
held back. They would just cease to enjoy the higher hydroponic growth
rate.
5. I've not had good luck with small transplants. The recommended medium
is a 1" cube of rockwool wedged into the foam. Rockwool holds too much
moisture for cacti and succulents and they tend to rot. The airstone just
can't push enough oxygenated solution up from below. I've got a bunch of
mixed specimens growing in jars now and will be transplanting them onto
green fiberglass when they reach 1 cm or so size. The fiberglass has a
"solid" side and a side which is just random fibers. I'm going to make a
plug with the solid side up and make a 1/8" hole in the it for the plant.
The roots won't dangle but will be supported by the random fibers below.
Solution and bubbles should still penetrate to root level.
Hope this helps!
Bob Cruder - bcruder@miaco.com
### IId
From: Carl.Gustafson@cbis.ece.drexel.edu (Carl Gustafson)
Subject: Re: More Hydro Questions/Reply
Bob,
A question from total ignorance:
>5. I've not had good luck with small transplants. The recommended medium
>is a 1" cube of rockwool wedged into the foam. Rockwool holds too much
>moisture for cacti and succulents and they tend to rot. The airstone just
>can't push enough oxygenated solution up from below. I've got a bunch of
>mixed specimens growing in jars now and will be transplanting them onto
>green fiberglass when they reach 1 cm or so size. The fiberglass has a
>"solid" side and a side which is just random fibers. I'm going to make a
>plug with the solid side up and make a 1/8" hole in the it for the plant.
>The roots won't dangle but will be supported by the random fibers below.
>Solution and bubbles should still penetrate to root level.
Would it be possible to take the foam and cut larger windows, possibly with
fiberglass window screen cleverly attached to the underside, and place
large areas of the furnace filter in these cutouts for seed sowing? One
problem I could see would be removing the green fiberglass filter from the
seedlings at a later time; this would seem to involve surgery.
Inquiring minds want to know...
Carl Gustafson
### IIe
From: waverheu@vub.ac.be (Willy A Verheulpen)
Subject: More hydro questions :-)
Thanks to Bob Cruder for explaining some basic techniques to
apply hydroponics but I still have some additional questions.
1) What is the need of using the non-rotting fiber? Is it not
enough to make the holes large enough to make the plant "float"
freely into them? Would this not be better to prevent stem base
rot?
2) I would have guessed about the oxygenation but is the "air stone"
approach not generating a problem with spitting around the solution?
& wetting the plants over & over ?
3) Do you use "colored" vessels to lock out light & prevent growth
of algae in the solution?
4) The root system in an hydro environment is substantially different
from the roots that develop in plain soil. Can one transplant hydro
raised plants easily into soil or is this a problem?
I recall from experiments here in the Plant biology dept. that they had
huge losses when transplanting agar-raised plants right into soil. The
solution seemed to be an intermediate step of transplanting in coarse
vermiculite.
5) Is this raft hydro system used for small plants germinated in
plain soil & transplanted subsequently? What about
adaptation losses?
OK that's enough for now :-) I am already set for some
experimental work!
Thanks to all! (but especially to Bob C)
Willy
### IIf
From: (Bob Cruder)
Subject: Rotting Caudex/Hydro?/Ariocarpus/Citric Acid
Ryan's Rotting Caudex:
I move many of my specimens out onto my deck in summer. About a month
back we had an unusual rainy period. It killed two lithops and rotted the
tuber on a night blooming cereus. The top of the cereus was OK.
As an experiment, I removed obviously rotting tissue and set the end in
3% hydrogen peroxide. It dissolved/sterilized the damaged tissue but left
the live tissue unharmed. I then followed common wisdom which was probbly
a mistake and let the bulb dry hoping that it would scar over. Instead,
it dessicated, losing almost all of its volume in the process.
I did stick what was left into my raft hydroponic system. In the last two
weeks, the residual bulb tissue has sloughed off with no obvious rot. The
top of the plant looks good and I am awaiting root growth.
I would recommend the technique to anyone trying to save a prized
specimen and would suggest one further step. Eliminate the raft system
and use a cool mist humidifier of either the centrifical or ultrasonic
variety to blow a very weak (100-200 ppm) solution on the remaining
caudex from below. There will be three main effects.
1. The high relative humidity will prevent wilting.
2. The high oxygen level prevents rot.
3. All of the plant surfaces absorb water and nutrients even without
roots, especially the undersides of leaves.
Many plants which do not root well, even with hormonal treatment, do root
with this aeroponic technique without hormones and do not rot even
without fungicides. I am currently trying to root a yucca head in the
raft system with NO pretreatment except for trimming out obvious rot.
Time will tell.
Hydro Questions:
Carl Gustafson has asked about using the green filter fiberglass as a
seed starting medium and wonders about removing the fiberglass from the
roots later. I intend to do such an experiment regarding germination but
already know the answer regarding removal.
Don't even try! I've used that same fiberglass to cover drain holes in
pots. Roots eventually grow through it and the fibers spread without
girdling the roots the way that wire screen does. I just cut away as much
as I can without cutting any roots and leave the rest attached to the
root mass when transplanting.
Ariocarpus:
I just received my order of ariocarpus from Mark (SPNOVA@aol.com). They
look great and are perfect experimental subjects for alternative culture
techniques. Since they grow so slowly with conventional techniques, any
documented improvement would be a real triumph.
Not knowing how many Mark has left, interested parties should contact
him. He who hesitates...
Citric Acid:
I had earlier recommended citric acid for adjusting PH in a hydroponic
solution. An interview in the winter issue of Growing Edge disagreed,
saying that the plants themselves consume the citric acid, raising the PH
of the solution. An earlier article in the same issue did say that
whatever citric acid is absorbed enters directly into the normal citric
acid metabolic cycle an merely serves as a source of energy.
While this may be a problem when growing peppers, (the main product of
the interviewee's system) it may be a positive boon for C&S growers. If
the citric acid becomes a supplemental energy source for the plants, one
may achieve growth rates comparable to grafting and avoid the
fermentation problem seen when adding sugars to a nutrient solution.
The only downside is frequent PH checking and addition of more citric
acid. Anyone else want to try?
Bob Cruder - bcruder@miaco.com
### IIIa
From: (Bob Cruder)
Subject: Root Temperature
Steve Barton described the value of bottom heat when growing tricho's.
Perhaps some background info would be of value.
Root metabolism varies with temperature in an inverted U curve for most
plants. At low temperatures, chemical reactions slow. At high
temperatures the solubility of oxygen in soil moisture drops, eventually
causing the root metabolism to drop due to partial suffocation. In
hydroponics, for a wide variety of plants, the optimum is 65-75 F.
Some minerals become less soluble below that temperature as well. Calcium
and phosphate precipitate out more readily and do not redissolve easily.
At higher temperatures (90 F and above) carbon dioxide becomes less
soluble. Free bicarbonates turn to carbonates and precipitate out. This
is the process that creates boiler scale.
Water and solutes dissociate more at higher temperatures. This causes the
PH to drop even when no acid or alkalii has been added. Since optimum
solubility and availability of most minerals is found with PH from about
6-7, temperature-induced PH shifts may help or hurt.
The safest policy is to aim for the 65-75F range, measure the PH after
soil temperature stabilizes and if needed, reset the PH with additives in
your watering solution.
Cacti and succulents don't need a lot of water but may suffer from
shortage of specific minerals. In addition, there may be chemical
messengers generated by the roots which slow the growth rate during dry
periods. Clearly, the plant as a whole responds to changes in root health
even when hydration is not compromised.
Would anyone care to measure growth rate against root temperature when
oxygenation, PH and mineral (at least NPK) levels are controlled?
Bob Cruder - bcruder@miaco.com
### IIIb
From: (Bob Cruder)
Subject: Accelerating growth in cacti
In habitat, the major growth limit is availability of water. When the
plant dries beyond a certain point, it no longer converts stored
carbohydrates into new tissue at the growing tip. It also opens its stoma
less to avoid moisture loss and thus limits CO2 intake. Photosynthesis is
thus reduced. Since less light is needed for that purpose, the plant
often produces more red pigments to at least reduce the photoageing of
existing tissues. When the plant is watered, the pigment takes time to
dissipate and there is a short-term decrease in photosynthesis even
though growth at the tip recovers quickly.
In cultivation, the limitations come from the low surface to volume ratio
of the columnar or globular form. One cannot increase the available area
for photosynthesis and transpiration but can make most efficient use of
what is there.
1. Supply as much light as possible short of burning the plant. Sunlight
is stronger than all but a focused arc tube but usually contains
significant UV. Limit the UV with window glass that absorbs it. Use arc
lamps to extend the daylight rather than supplement it. Much of the weak
stems are actually elongation due to insufficient light. One can prevent
the elongation by limiting water and nutrients but that merely hides the
symptom.
2. Control temperature. The CAM metabolism of cacti doesn't really work
below about 70 F and you can get tissue damage if the central
temperatures get much above 100F. Within that range, they are most
efficient.
3. Supply moisture. Keep the soil as continuously damp as you dare. A
well drained medium can be watered daily without risking rot in most
species. Stem splitting is due to supplying lots of water after a long
period of drying when sugars become concentrated in the tissues. If you
never let the plant get really dry for long, you'll not get splitting.
4. Supply minerals. Hydroponic tests in other species have shown that
plants build supportive tissues faster and stronger as the conductivity
of the solution is increased. This effect continues even beyond the point
where externally measured growth starts to decrease. Unfortunately, the
tests did not show what minerals were most important and which ones, if
any, were counterproductive. I would guess that one should avoid high
concentrations of nitrogen since so many anecdotal claims abound for
plants that got tall but weak from that mineral.
5. Protect the plant. Fast vertical growth may outpace the production of
cuticle cells and waxes. The resultant skin may be easily injured. I have
found it somewhat more prone to sunburn as well. In my experiments, the
skin does eventually thicken but it may take a year to become
indistinguishible from slow-growth tissue.
6. Supply CO2. This is a guess that I haven't tested. Even with all of
the above, cacti suffer from limited ability to transport CO2. Since CAM
plants transpire in darkness, lengthening the day to supply more light
may exacerbate this problem. CO2 supplementation during the dark period
could be of great value. Would anyone like to try it?
7. Try hormones. I've induced growth in some cacti that hadn't grown for
years by spraying with seaweed extract. Since they were well-fed, I must
presume some hormonal rather than foliar feeding effect. Perhaps a reader
can comment or would like to pursue a controlled experiment.
Bob Cruder - bcruder@miaco.com