Cacti that grow on limestone

[adetheproducer]

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?

Well I thought simply there will always be an organic element to any soil anywhere on earth so why avoid it. Even if you look at high altitude plants like blossfeldia or others like l.williamsii and a like growing out of cracks in the rocks. They will accumulate organic material like old flowers and seed pods around them. So I think a little is good. Also it helps with the consistency of the soil mix.

[CactusFanDan]

Perhaps in relatively high rainfall arid areas. The drier an area is, the more it tends towards bare rock, so a lot of high andes species will grow on totally bare rock. I guess it matters little. I add a bit more to my mix than 5%, but it still doesn't seem like much.

[iann]

My final mix will be about 10% peat. Perhaps a little less since I remove any big chunks from the mix. Compared to the rest of the mix which is cat litter grit, and sandy loam, the peat probably contributes more nutrient holding capacity than the whole of the other 90%. There are some desert cacti that I'm sure want a higher level of organics than that, not that they get it in my greenhouse

[adetheproducer]

Well the organics in mine is worm casts from the back garden and soil from local oak forest, the loamy stuff under the initial leaf mulch. I also use a little natural clay in lumps from the same forest, they hold water well while being dry to the touch then plenty of limestone chips gravel and sharp sand.

[sabotenmen]

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.

I agree. Here in Japan, bagged commercial cacti mixes are usually pumice based. Great, of course, but I have found that not all cacti grow well in it. Alkaline lovers grow better in (inert) pumice than acid lovers. I had a Gymnocalycium in pure pumice, and it didn’t do anything. When I repotted it in a loam/choir/grit mix (ph 6.5), it immediately started to grow. I would not put plants like Gymnocalycium, Parodia, Rebutia, Sulcorebutia, Weingartia, or most Brazilian cacti in a pure mineral mix. I use the commercial cactus pumice mix for North Americans, Chileans, and Mexicans. I don’t like adding any alkaline material to my mixes; I read too many negative things about it. Don’t know about acidity of loam in “The Far West”, but here, peatless loam has a ph of around 7.75, which is already slightly alkaline, I don’t think it would be necessary to make it any more alkaline for "chalk" loving plants. Bagged soil with peat has about 40 percent peat in it, which gives it a ph of about 6.25 . This would be good for the South Americans; however 40 percent peat is too much. I mix it 50/50 with a mixture of loam/choir. I cut this mix with 30-50 percent grit. I usually don’t use pumice in an organic based mix, I prefer grit.

[DaveW]

The Cactaceae grows over a wide area with many different climates, altitudes, and as Ian says soil types. It is remarkable that most will grow in the same potting mix with no problems. However the simple remedy is if a few are not doing well in your favourite mix, be that purely mineral or peat based, try another mix even if only for that plant. Also as said before certain mixes suit certain climates. Mixes that retain moisture for long can lead to rot in sunless UK, whereas they may be desirable in hot climates where plants in pots will dry out too quickly.

Is there anybody who has been growing plants for many years and still uses the same mix they originally started with? Human nature being what it is we all tend to try the new "wonder mix" fad in the hopes the plants will grow better than they did before.

[Steve Johnson]

Wow, it's good to have such a thought-provoking thread here!

I would not put plants like Gymnocalycium, Parodia, Rebutia, Sulcorebutia, Weingartia, or most Brazilian cacti in a pure mineral mix.

My 3 Gymnos, 2 of my Sulcos, and my Frailea castanea are doing quite well in pure pumice/DG mix (the DG is there only to make the pots heavier so they don't tip over in high winds). Maybe it's because I'm acidifying my tap water -- does wonders for moisture and nutrient uptake when the cacti are in growth. I got the latest Sulco (aranacea) in July, so I'll have to see what it does through a full growing season. Ditto with the Rebutia heliosa and Weingartia neocumingii brevispina which arrived too late to start establishing. My only other Brazilian is an Uebelmannia pectinifera I received in April. It didn't do anything last year, although the plant came with a tiny set of roots. My feeling is that it was concentrating its energies on establishing a healthy root system. If I'm correct, the pectinifera should start producing new apical growth when the temperature curve looks more like Summer. The verdict on these newer guys will come in later this year.

Is there anybody who has been growing plants for many years and still uses the same mix they originally started with? Human nature being what it is we all tend to try the new "wonder mix" fad in the hopes the plants will grow better than they did before.

There's no such thing as a universal "wonder mix", and yet people keep chasing after it. Human nature being what it is, I think that's what separates the dedicated enthusiasts from the fadists who get into the hobby and then leave after a few years. I'm in contact with only a handful of hobbyist cactus growers who've been in the pursuit for more than 10 years, so that represents a tiny sample size -- I honestly don't know if it's common practice for veteran growers to make constant changes in their potting media.

Since all cacti in general grow more slowly than non-xeric plants, it can take years for problems to show up if a given mix isn't performing. While I'd have to know them on an individual basis, it would be interesting to find out how many of these veterans are using the same mix they came up with a long time ago. Maybe this is an arbitrary benchmark, but if your cacti are doing well after 5 years in the same mix, I'd stick with it unless you really think they could be doing better. This something we all have to figure out for ourselves, but tinkering without a certain amount of thought behind it seems kinda pointless.

[DaveW]

The problem as well these days is some of the components of your mix you originally started with may be no longer available. In the UK they are trying to remove peat from everything and substituting for it what amounts to composted rubbish!

Originally the John Innes formula's called for virgin loam. To quote from a gardening book of that time:-

" Virgin Loam - The Formation Of Soil

The choicest production of nature for gardening purposes, is the simple natural loam of a fertile pasture, which has not been cultivated for many years. A thick old sod, with a bit of turfy loam, which has not been disturbed by the plow for a long time, contains the elements of a good soil, in a condition which can scarcely be imitated by the art of man."

Nowadays what is sold as loam is just any old topsoil off a previously well cultivated field or garden. One reason many of the new soilless composts have been invented is good loam from fields that have lain fallow for years is now scarce in the UK.

[Steve Johnson]

Nowadays what is sold as loam is just any old topsoil off a previously well cultivated field or garden. One reason many of the new soilless composts have been invented is good loam from fields that have lain fallow for years is now scarce in the UK.

We're fighting a similar battle here, and some US growers have reported a serious decline in the quality of commercial potting soils being used for cactus mixes. Apparently the manufacturers throw in any and all plant waste they can get these days, so it wouldn't surprise me if veteran growers are frustrated because they can't find the commercial soils they could rely on years ago.

Really sad if your formerly tried-and-true JI product ain't so tried-and-true anymore.

[adetheproducer]

Apparently the manufacturers throw in any and all plant waste they can get these days, so it wouldn't surprise me if veteran growers are frustrated because they can't find the commercial soils they could rely on years ago.

Really sad if your formerly tried-and-true JI product ain't so tried-and-true anymore.

Yeah I bought a few compost sacks last year for dill, cucumber, pumpkins and general garden use and no matter where I got them they where all about 50% wood, twigs and cuttings at varying degrees of decomposition. Also you can smell the fungi in it, like the mushroom section in you local supermarket. I pretty much decided to source soil from natural places where in would not hurt you take a scoop or two.

[StephenG]

Not quite about growing in limestone - but related I think.

Where I live the water pH is around 7.2 - quite hard. I decided to use hydroponics techniques to soften the water to 6 for watering, following advice that cacti generally like soft(er) water. Most seem OK and some clearly flourish but one in particular (I think a Rebutia) developed a brown 'scale' all over. The plant was not rotten, and as the source plant had always been watered with tap water I resumed using tap water. It's now producing new bright green shoots (and new growth at the tips and sides is showing green). So - it seems that this plant in particular likes a degree of hard water and so perhaps a soil with a higher than usual pH for cacti. (Another Rebutia - definite this time - also has brown tips which now are mostly beginning to give way to green tips).

So unless the 'scale' effect was due to something else it seems possible it was due to a surfeit of soft water. (The plant has been in the same soil for a couple of years; in the same position before soft water watering and since - so not likely to be sun damage). I guess the wider question of growing on limestone depends on where the plant originated from, and without high quality detailed botanical info we often don't know.

[iann]

Might be coincidence. There is a huge risk in our hobby of thinking that "whatever I tried last" is the reason a plant is dying or thriving when usually it was something that happened long before that or just a random throw of the dice.

Rebutia of all cacti is one of the last you should be using hard water on, not that your water is particularly hard (in fact pH 7.2 probably isn't hard at all, probably just nudged up slightly by the water company to avoid pipe corrosion). The only connection I can think of between "limestone" and "Andes" is that they're both towns in the same state. Can you guess which? The Andes mountains are almost entirely igneous.

Don't know what the scale would be. Mites? Mites love Rebutias. Almost anything can do this though, fertiliser burn, pesticide scorching, anything that scars the skin, the end result is the same orange-brown crustiness. Perhaps even some reaction to the chemical you are adding to the water?

[DaveW]

"Where I live the water pH is around 7.2 - quite hard. I decided to use hydroponics techniques to soften the water to 6 for watering, following advice that cacti generally like soft(er) water. Most seem OK and some clearly flourish but one in particular (I think a Rebutia) developed a brown 'scale' all over. The plant was not rotten, and as the source plant had always been watered with tap water I resumed using tap water. It's now producing new bright green shoots (and new growth at the tips and sides is showing green). So - it seems that this plant in particular likes a degree of hard water and so perhaps a soil with a higher than usual pH for cacti. (Another Rebutia - definite this time - also has brown tips which now are mostly beginning to give way to green tips)."

A quote from the following link:-

"3. Observable Effects of Trace-Element Deficiency

There is a particular form of nutritional deficiency characterized by the development of uneven orangey-brown or light-brown necrotic scars near to the growing point, and in bad cases the death of the growing point. Within my own collection of plants those most evidently prone to this affliction are to be found within the genera Lobivia, Trichocereus, Rebutia and Sulcorebutia, though I have also seen signs of the described syndrome in other genera, including e.g. some Echinopsis, Coryphantha and Echinocereus. The syndrome has been described and well illustrated by K,-P. Gruber & A. Hazelgrove in BCSJ 1 (1983) pp 45-46 and by R. Mottram in BCSJ 4(1986) pp.9-13. It appears in alkaline inorganic composts, and is due to a trace element lock-up. Recurrence of the condition can be avoided by lowering the pH to some value below 6.5, the effect of which is to render the trace elements available by bringing them back into solution.

In the case of plants in soil-based or other strongly buffering media the lowering of the pH requires the administration of a considerable amount of acid, which can however be quickly yet safely supplied by waterings with solutions of aluminium sulphate (i.e. hydrangea colourant) – see our Branch Newsletter 1(1995) No.1.

The above mentioned pH-vulnerable plants and others like them are often called ‘lime-haters’ for reason that calcium carbonate (CaCO3) is the most commonly encountered source of alkalinity. Calcium is however a necessary nutrient, and cacti could in that respect be truly described as ‘calcium lovers’. Their calcium requirements can be met by use of the neutral salt calcium sulphate in its hydrated form CaSO4.2H2O, the common name of which is gypsum. The unhydrated form is called Plaster of Paris; the use of which I would most certainly not recommend!

The ‘lime-haters’ are also somewhat liable to a more superficial form of epidermal necrosis, in which large areas of the. outermost layer dry out and become uniformly whitish or pale brown. This shallow necrosis seems to occur in conjunction with dryness and summer sunshine. It is not at all like sunburn however. It is often identified as due to red spider attack, but in spite of careful examinations I personally have never found any examples of the alleged offending Acaridae nor of their webs. I think it is much more plausible to suppose that this syndrome is just another manifestation of the pH-linked trace element lock-up.

Cacti endemic to limestone areas, such as Astrophytums, Strombocactus disciformis, etc. do not normally exhibit any symptoms of trace element deficiency and in fact grow quite well even under a mildly alkalinic (below 7.5, say) inorganic soil-based regime. Quite generally it is thought that limestone tolerant plants produce acidic root exudations which unlock the required trace elements. Consistent with this concept is the well-established fact that no plant will grow in a hydroponic set-up unless the nutrient solution is acidic. For it is obvious that under hydroponic conditions the root exudations will leak away as fast as they are produced."

http://www.bcss-liverpool.pwp.blueyonde ... part_2.htm" onclick="window.open(this.href);return false;