Mineral based compost

[gerald]

What is it exactly? I've just received a cactus in the post (Escobaria hesteri to be precise) and unlike the other cacti in the package there is a note with it that specifically states it should be planted in a 'mineral based substrate'. I presume that means cat litter/grit/perlite only? Advice/explanation welcome.

[iann]

No, or very low, peat/compost/bark/wood.

[CactusFanDan]

Pretty much just grit/cat litter/perlite/pumice or whatever you feel like using. Some species of cactus which are known to actively digest rock in habitat are supposed to really benefit from a mineral mix composed of certain rocks which provide nutrition to the plant. I've seen some czech growers use this method of mineral mix and no fertiliser for Ariocarpus with quite nice results. However, I wouldn't single out E. hesteri for needing a mineral mix. It'd help to keep it nice and compact, but it's not necessary.

[DaveW]

Strictly speaking containing no organic ingredients, but as Ian says some do contain a small amount. Those who use purely mineral mixes usually fertilise with half strength fertiliser virtually every watering, so really it is more akin to hydroponics than plants growing on rocks or mineral soils in habitat.

There are two schools of thought growing cacti. Some prefer the plants to look as similar to plants in habitat as reasonably possible, whilst others treat them as normal cultivated plants aiming to produce the maximum possible growth in the shortest possible time. Some claim the latter are abnormally green and bloated compared to habitat, but the judges seem to like them so they do win shows. Probably the happy medium is a potting compost somewhere between the two producing reasonable growth, but plants not too far out of character compared to habitat.

See:-

http://www.cactus-art.biz/note-book/Dic ... tratum.htm

http://www.kadasgarden.com/Csoil.html

http://www.cactiguide.com/pdf_docs/hexalog-engl.pdf

Some claim plants growing on limestone need it in their compost, others claim it is in fact a growth retardant that keeps the plants from getting bloated and so looking naturalistic like habitat plants. Over the generations cacti have been grown successfully in most compost formulations, from virtually just broken brick, or burnt clay recommended in an early book on cactus cultivation by Endean, to mostly peat based composts favoured by Continental commercial growers..

[Milan]

I have several Esc. hesterii for some 15 years and they are ok in fine sand with just a little bit of loam. Esc. hesterii is very frost hardy if dry, mines were many times bellow -20°C.

[iann]

JI is fine for these plants. It contains some peat (or who knows what in some brands these days!) but by the time you've diluted it with cat litter and grit, it doesn't seem to be at harmful levels. Escobarias certainly grow well in this type of soil. Some more tips: don't overpot, water generously in spring, but be prepared to leave them drier in summer heatwaves.

[Milan]

Based on my experience on habitats in Argentina and Chile, I can say that most of cacti grow much faster in habitats than in our pots. There are exceptions in extremely dry regions, say in Chile on coast north of La Serena or in Argentina in the desert of San Juan province. Certainly, cacti which are normally large like Eriosyce sg. Eriosyce or Soehrensia grow very fast but even I observed a population of Rebutia senilis in Qda. Escoipe which in 2009 was almost destroyed by rock slide and in 2012 the rock which in 2009 was bare, was covered in moss and lichens and in this moss there were several groups of Rebutia seedlings with flowerbuds already.

[DaveW]

I think people forget that cacti apparently just growing on bare rock are usually growing in crevices where some organic material has collected over the centuries, though not to the same extent as in more fertile soils, even if it was just blown in by the wind. Also though narrow the fissures may have a greater volume for root growth than the pots we grow them in.

Anybody who has grown cacti in an open bed knows those in pots are Bonsai'd and much slower growing. Mind you the countries Milan mentions mostly have better cactus growing climates than the UK for faster growth

http://www.sipaliwinisavanna.com/docs/d ... tation.pdf

http://www.sipaliwinisavanna.com/docs/d ... _plate.pdf

http://www.sipaliwinisavanna.com/docs/d ... slopes.pdf

See the comments under "Soil and Potting" in the following link:-

"Contrary to a common misconception, limestone soils are not highly alkaline - limestone itself is virtually insoluble in water and the amount of calcium bicarbonate, which has only a very mildly alkaline reaction, produced at any one time is tiny and transient as it is quickly consumed by neutralizing acidic constituents in the soil (humic acids etc.), facilitating the release of essential minerals from complex clay structures and by the plant itself. Limestone soils are, therefore generally slightly on the acid side of neutral to slightly on the alkaline side of neutral (pH7.0)."

http://www.living-rocks.com/adult.htm

It is obvious too that the north of Chile has been gradually getting dryer over the centuries. Plant populations like Islaya krainziana that were in quite a reasonable state in Ritter's days now appear to be extinct in northern Chile, though some still exist over the border in Peru.