Cacti that grow on limestone

[mg2007]

I have been reading up on som species of cacti that I want to grow, and noted that they grow on limestone. What adjustments should I make to the soil for these plants?

[DaveW]

There was always a debate as to whether cacti grow on limestone through choice, or simply through necessity to avoid competition from more vigorous plants. Certainly for most cacti limestone in the compost does not seem to be a necessity and some even claim it can be a dwarfing agent to keep the plants more natural looking rather than the out of character vigorous growing plants you often see in shows.

Two opposing views on the subject:-

http://www.cactiguide.com/pdf_docs/hexalog-engl.pdf" onclick="window.open(this.href);return false;

http://ralph.cs.cf.ac.uk/cacti/Cactus%2 ... linity.pdf" onclick="window.open(this.href);return false;

The fact is cacti will grow in most potting composts to a greater or lesser extent and no controlled scientific work seems to have been done with significantly large numbers of the same species to find the truth, or even if it varies species to species for the terrestrial cacti. Also it depends whether you prefer your plants to look more akin to those in habitat, or the often bloated over fertilised show winning plants as to what your ideal soil mixture and cultivation is.

Many growers use the same compost for all their terrestrial cacti, be they North or South American. Whereas others claim N. American ones prefer a neutral or slightly alkaline compost and S. American ones slightly acid. As always with cultivating plants it's what works for you, but don't get too hung up on needing very complex compost mixes.

[iann]

Which species are you looking at?

[CactusFanDan]

I've got all sorts of cactus species growing and none of them get any limestone, even though some are recommended to be grown with added limestone. All of them grow fine in my slightly acidic soil mix.

[adetheproducer]

I already use lime stone but have done a fair bit of reading and thing my next experiments with soil are going to include gypsum. Most of my cacti come from mexican desert where gypsum is a major ingredient in the soil so I am on a mission top collect some recycled plaster board or for the american among us some dry wall. It seems this is already used a a soil additive so will include on my next project.

[DaveW]

Not sure UK recycled plaster board is a good for plants unless you know what's in it, so do a small test first. I read somewhere there are often other ingredients added besides natural gypsum, some from flue gas desulphurisation. Probably Ian will know better though if this is a safe material for plants?

"To manufacture plasterboard the raw material is firstly processed by grinding the rock to powder. The powder is heated at around 150°C, causing it to lose about three-quarters of its water, and is then called hemi-hydrate gypsum plaster (CaSO4.½H2O) – commonly known as Plaster of Paris. It is then re-mixed with water to form a paste, which is spread and sandwiched between the layers of facing paper. When the paste sets and hardens, it has effectively reverted back to being gypsum rock."

http://www.smartwaste.co.uk/filelibrary ... gypsum.pdf" onclick="window.open(this.href);return false;

A friend got me some lumps of gypsum which I crushed for my plants from where they mine it for plasterboard (British Gypsum), since quite a bit of gypsum is mined for plasterboard in our area.

Some claim using plasterboard waste is OK though:-

"Gypsum Addition

The mineral gypsum can help improve soil in multiple ways. According to Ohio State University, gypsum increases the calcium levels in soil which can help prevent soil from crusting when it dries out. All gypsum adds calcium and sulphur to the soil, and mined gypsum also adds magnesium. These nutrients help with plant growth. Another benefit of using gypsum to remediate soil is that gardeners can obtain recycled gypsum from old drywall and industrial plaster of Paris casts, which helps the environment by keeping material out of landfills and reducing the need for gypsum mining for agriculture."

Also unlike lime or limestone I believe gypsum does not normally alter the PH of the compost, so plants in nature growing on gypsum do not necessarily like alkalinity.

http://www.cmtmi.com/gypsum.asp" onclick="window.open(this.href);return false;

http://cactusnursery.co.uk/ph.htm" onclick="window.open(this.href);return false;

[Juliska]

I may not be reading the initial question correctly.

However, I'm a geologist. Our native species of cacti grow quite fine locally on limestone. The most common Eco niche is limestone exposures, bentonite clay, etc. Lots of other non cacti growing beside them...composites,legumes, grasses.

I've worked lots of places across the western USA and the same. Lots of cacti at fossil research sites in the Mojave, Great Basin deserts, etc. Often the dominant rock is limestone.

I never buy any commercial cactus mix. I just add local rock bits, grits, sand to the soil . Most of this is limestone. Never had any indoor or outdoor cactus not do fine regardless of of its origin.

[DaveW]

Marlon Machado, a Brazilian botanist, maintained the cacti that grew on limestone only grew when they got acid rain and as soon as the limestone turned it really alkaline they stopped growing. How true that is really only a controlled experiment would prove. As Dan says though in cultivation they all seem to grow well in a slightly acid soil and don't need limestone.

[iann]

Marlon Machado, a Brazilian botanist, maintained the cacti that grew on limestone only grew when they got acid rain and as soon as the limestone turned it really alkaline they stopped growing. How true that is really only a controlled experiment would prove. As Dan says though in cultivation they all seem to grow well in a slightly acid soil and don't need limestone.

How would anyone know, since that is the only kind of rain? And everyone says all plants grow just fine in their type of soil, whatever it happens to be. Except for the ones that died and were conveniently forgotten or just got tagged as "too difficult"

I have also been meaning to try out gypsum for some of the specialist gypsophiles. I've tried a couple of them with limestone and they didn't seem so keen. For example, Turbinicarpus lophophoroides tends to look chlorotic in alkaline conditions, but then it isn't the easiest plant to keep happy anyway. Same goes for the gypsum-endemic Pediocactus, so I can't really say what the answer is.

[DaveW]

I did read once that falling rain watering plants is not the same as using stored rainwater from a water butt, since the stored rainwater quite quickly changes in the butt. How true that statement is though I don't know, since I have never tested falling rain against that stored in my water butts? Of course one answer may be rainwater falls directly whereas water in water butts is collected off roofs with various types of covering and pollution covering them, which could affect the PH and chemical composition of the butt water.

It does seem to be the case though that putting your plants out in a rainstorm seems to perk them up more than all the rain water in the greenhouse from the water butt.

[iann]

It seems to me that the standard UK practice of only watering when the sun shines is a mistake.

[adetheproducer]

It seems to me that the standard UK practice of only watering when the sun shines is a mistake.

Not really they will do better if only watered when yhe soil is dry. I live in Wales and water mine from early spring so March onwards until october. And we certainly dont get that many sunny days. I use Lime stone with most of my cacti for drainage and minerals. Going to try gypsom next spring and see how thst does with watering.

[Gary]

...my next experiments with soil are going to include gypsum....so I am on a mission to collect some recycled plaster board or for the american among us some dry wall. It seems this is already used a a soil additive so will include on my next project.

Unless I got this wrong you live in the Rhondda, sorry Welsh geography isn't my specialist subject but anyhow rather than using plasterboard with it's added chemicals, if you had a friend or friend of a friend who worked at the cement factory in Aberthaw (about 20 miles or so from the Rhondda depending on exact location) I'm sure they would be happy to get you a "small" amount of gypsum "sweepings" that would probably last you several life-times of plant growing. If you don't have a friend there it couldn't hurt to send a short suitably worded begging letter to their Production Manager.

Just a thought.

Good luck.

[CactusFanDan]

I already use lime stone but have done a fair bit of reading and thing my next experiments with soil are going to include gypsum. Most of my cacti come from mexican desert where gypsum is a major ingredient in the soil so I am on a mission top collect some recycled plaster board or for the american among us some dry wall. It seems this is already used a a soil additive so will include on my next project.

Gypsum doesn't seem to be necessary. I've got Aztekium hintonii growing on it's own roots in the same stuff I use for well... everything. It isn't bloated (well it probably is compared to a habitat plant), it isn't unhappy, it is growing. Geohintonia seedlings grow like weeds in the very same soil mix. I keep Ariocarpus in the exact same soil, as well as Epithelanthas and other 'limestone-lovers' and they grow fine. Not too fat, not too lean, very green in colour.

I did read once that falling rain watering plants is not the same as using stored rainwater from a water butt, since the stored rainwater quite quickly changes in the butt. How true that statement is though I don't know, since I have never tested falling rain against that stored in my water butts? Of course one answer may be rainwater falls directly whereas water in water butts is collected off roofs with various types of covering and pollution covering them, which could affect the PH and chemical composition of the butt water.

It does seem to be the case though that putting your plants out in a rainstorm seems to perk them up more than all the rain water in the greenhouse from the water butt.

Fresh rainwater contains hydrogen peroxide, which diminishes in concentration as it's stored. Peroxide has the effect of helping to deliver oxygen to the roots of plants, so maybe that has something to do with it. I'm a big fan of adding peroxide to water (albeit in much higher concentrations than is found in rainwater). Plants really enjoy it. Rainwater mops up all sorts of atmospheric muck as well, which will probably dissipate with storage. In particular acidic gases like oxygen, NO2 and SO2 will bubble out after rainwater has been allowed to stand.

[DaveW]

That's what I was trying to recall Dan, the difference between falling rain and stored rainwater. I knew I had read it somewhere. I seem to recall also when you acidify water for plants or use stored rainwater, if you leave it standing around for days the PH also alters?

I think a friend of mine got it correct about cactus composts when he said "they will grow in virtually anything if you get the watering right". I suppose that would mean the correct PH water and any fertiliser needed. When I see some of the composts mentioned on here and fertilisation needed the plants are virtually being grown hydroponically anyway.