Cacti that grow on limestone

[adetheproducer]

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.[/quote]

I have been doing some more reading and it seems we have good source of gypsom in the form of alabaster on the coast between barry and penarth. So will go on a nature hunt much more fun than visiting a factory. I have seen the mineral myself in the past just didn't know it was gypsum.

[Steve Johnson]

When I see some of the composts mentioned on here and fertilisation needed the plants are virtually being grown hydroponically anyway.

Sorry if I seem to be getting hung up on semantics here, but to me "compost" means the presence of organic material in a cactus mix. I grow the vast majority of my cacti in pumice and DG that has the "play ground" sand sifted out. There's zero compost to be seen there, and the pumice/DG mix is in fact soil-less. Calling it hydroponic growing would be accurate, and fertilizing every time the cacti are being watered in the growing season is a requirement. A few of my cacti do need a certain amount of soil in the mix because their roots are too fine to properly support a pure pumice/DG aggregate. Although the soil I use is lightly composted, the plants I keep in a mineral/soil mix are definitely not being grown hydroponically. Such being the case, fertilizing every single time isn't such an absolute requirement. Please bear in mind that I can speak only for my own particular setup, and I don't know if growers outside the southwest US would be able to do it. Hence the reason why different cactus people need to find out what works best given the ingredients they have available.

Gypsum doesn't seem to be necessary.

I'm with Dan, and IMO it's over-thinking when we assume that calciphyte species growing in the wild should get some limestone in their potting medium when they're brought under cultivation. Perhaps Dave is correct about limestone being a natural growth inhibitor, but is the absence of it really a problem for our potted calciphytes? I suppose it depends on whether or not someone is trying to replicate habitat growth. I honestly don't know if there would be a qualitative difference, so I'll leave it to those of you who find that there is. As for me, the few calciphytic cacti I have are growing just fine without limestone. However, if anyone would like to experiment with limestone in their mix -- go for it.

[iann]

In the UK the word compost is used generically for just about any bagged potting soil whether they have any composted materials or not. Increasingly though, modern composts include at least some composted material such as woodchips as well as the obligatory peat. My potting mix has zero composted organic material, although it does (or at least should according to the specs) contain about 10% peat.

[Gary]

So will go on a nature hunt much more fun than visiting a factory.

Couldn't argue with you there.

[mg2007]

Wow, I had forgotten I had posted the question! It prompted quite a discussion, I see. The consensus seems to be that ones growing on limestone in nature do not need any special soil in cultivations. I had not had any particular species in mind at the moment but had noticed quite a few listed in descrip[tions as growing on limestone.

BTW, Juliska, I also was a geologist, though due to medical problems my career as a filed geologist was short.

And yes, even pure rainwater, unaffected by pollution, is mildly acidic, 5.7 to be exact.

[adetheproducer]

the reason I will be trying gypsom is down to the seedlings I have. I have got about 10 strombocactus disciformis and they are know to grow in gypsum/limestone soils so will attempt a more natural soil for them. But its likely to be experimented with before transplanting the seedlings there are about 3mm wide now so to small do anything with yet.

[DaveW]

As Ian says, compost is used in both senses in the UK Steve. In your sense as well as to indicate potting soil that is different from straight garden (yard) soil, since garden soil in a pot does not behave as it does in open ground, therefore has to be modified to provide a similar performance for potted plants.

At one time the only real humus material added to our potting composts would have been peat since John Innes composts were mainly used as a base. As Ian says though, since they are now discouraging peat all sorts of composted rubbish is being added as an alternative, since obviously most are intended for growing "normal" plants rather than cacti.

The first use of virtually pure peat based composts in the UK came about when Levington's introduced them being based on your American University of California peat based composts:-

http://www.actahort.org/books/7/7_20.htm" onclick="window.open(this.href);return false;

The original John Innes compost recipes were:-

http://gardenofeaden.blogspot.co.uk/201 ... mpost.html" onclick="window.open(this.href);return false;

As you will note JI 1-2-3 only differ in the amount of fertiliser added. Many UK cactophiles at one time used to use JI 1 or 2 with up to 50% extra potting grit added to improve drainage. Now many are copying the bonsai growers and starting to use purely mineral mixes, often including baked clay cat litter as one ingredient since pumice is not cheaply obtainable in the UK.

http://www.bonsai4me.co.uk/Basics/Basicscatlitter.htm" onclick="window.open(this.href);return false;

The difference between gypsum and limestone I believe is gypsum provides calcium without turning the compost alkaline?

http://www.soilsolutions.net/uploads/Gy ... Harris.pdf" onclick="window.open(this.href);return false;

[adetheproducer]

I have obtained some alabaster(gypsum rocks). I found them on caerphilly mountain so no worries about washing out any salt. Some of it I will crush into small chippings along with lime stone and make a mineral soil mix ready to repot my s.disciformis when they are large enough. I will keep some for decorative purposes too I think the colours will make the green of the cacti look great. I will endevour to keep updates on plant progess with this experiment.

[iann]

Is that gypsum or calcite?

[adetheproducer]

Is that gypsum or calcite?

It should be the gypsum variety thats the one that occures in the south wales area
http://www.museumwales.ac.uk/cy/800/?mineral=400" onclick="window.open(this.href);return false;

Take a look.

[LophoFan]

I found a huge bag of granular gypsum out in my back yard. I might give it a go. I have a bunch of ariocarpus and lophophora seedlings that will need to be potted into their new permanent homes. I need to find a good mineral soil mix for my rock feeders. Or I could just use miracle grow cacti mix (just kidding)

[adetheproducer]

I found a huge bag of granular gypsum out in my back yard. I might give it a go. I have a bunch of ariocarpus and lophophora seedlings that will need to be potted into their new permanent homes. I need to find a good mineral soil mix for my rock feeders. Or I could just use miracle grow cacti mix (just kidding)

Just make sure it hold up under repeative watering and drying. I started and experiment using lumps of gypsom plaster(plaster of paris) included in the mix. While the lumps seem quite stable in short term a lot of it washes away with repetative watering and turns the remaining soil into very dense mud, obviously not good for lophs or arios with the tap root.

[iann]

Just make sure it hold up under repeative watering and drying. I started and experiment using lumps of gypsom plaster(plaster of paris) included in the mix. While the lumps seem quite stable in short term a lot of it washes away with repetative watering and turns the remaining soil into very dense mud, obviously not good for lophs or arios with the tap root.

You might be surprised Wales is probably not the best place to use this sort of soil though.

[adetheproducer]

Just make sure it hold up under repeative watering and drying. I started and experiment using lumps of gypsom plaster(plaster of paris) included in the mix. While the lumps seem quite stable in short term a lot of it washes away with repetative watering and turns the remaining soil into very dense mud, obviously not good for lophs or arios with the tap root.

You might be surprised Wales is probably not the best place to use this sort of soil though.

Yeah very moist over here my plants are all currently in a quite gritty sandy loam which works well. My experiments at the moment are just pots of dirt at varying degrees of dryness and environments. Not risking any of actual plants just want some information before I move seedlings into more permanent homes. I have got one loph seed in my plaster/limestone mix in the which I doubt will germinate the surface does not hold the right moisture. Pretty much come to the conclusion soft gypsum is useless in our wet and cold climate. Limestone on the other hand is proving its self. My larger lophs are looking good nice and compact and flower regularly. My turbinocarpus suedopectinefra seedlings seem healthy since moving them in to a limestone and perished brick chips mix(about 95% mineral).

[CactusFanDan]

I've got to wonder if that 5% of your mix that isn't mineral is making much of a difference. Do you think it makes a significant difference?