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[dEEcor]

What properties should a soil have that suits most cacti?

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[Chicsa]

Might depend on local climate conditions.

I use a black gold cactus soil mix, and mix it sometimes with miracle grow that I've mixed with more perlite and sand. I found mine do best in really sandy mixes, and also do really well in my local sandy soil

[BubbleCat]

The whole mix should contain large quantities pf mineral material, as opposed to organic matter, afaik.

[Athena]

In my limited experience, soil for cacti should be free draining. I would also say generally any mix high in mineral particles as opposed to organic matter would be good, however, I have some cacti that I bought growing in chunky organic matter soil that don't seem to mind it one bit. So as long as the mix doesn't retain much of the water for too long, it should be fine.

[FewTrueSeed]

The black gold is what I use. Great mix!

[MadPlanter]

My personal cacti mix is roughly half sand and half non peat based potting soil with a lot of extra added perlite. Seems to work well for starting seeds and adult cacti.

[LSoares]

A cactus soil must drain fast but still have some retaining capacity (cacti need water just like any other plant). I personally favour pumice, lava, scoria - whatever you wish to call it, for they are basically the same apart from density - crushed bricks, some kinds of kittly liter, etc. Porous particles is what I look for. Sand is too heavy and perlite floats to the surface. Some kind of mineral(*) soil makes for the "fine" portion of the mix, and robust growers get a dose of worm casts. If you really must go for it, coir is better than peat (if not for other things, because it's environmentally friendly and sustainable). Mineral / inert mixes are too barren for cacti to live in, remember to fertilize.

(*)"mineral" in this case means "devoid of organic matter". If you can't find something like this, dig deep somewhere and choose the depth when the soil changes colour from dark (dark tones usually mean organic matter) to light.

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[Auxin]

This question has no simple answer.
The first layer of considerations has to be the cactus, you, and the world...
Different cacti can tolerate and appreciate radically different soils. A rich soil formulated for tomatoes which some of my trichocereus would absolutely love would kill an ariocarpus. Geohintonias can tolerate mineral soils that would be gradually lethal to most other cacti. There is a lot of variety in their needs and tolerances.
What you want from a cactus is just as relevant. Ever notice how Lophophoras in nature look little like those in cultivation, the same is true for most cacti because most people grow them in soils that foster faster, fatter growth. In cultivation the climate and soil determines what an individual cactus will look like.
Available materials should be considered as well. You'll encounter formulas that include materials expensive or unavailable in your area. When I go hiking I take along a big plastic jar just in case I find any good looking mineral to incorporate in mixes.

Books could be written about each of those three points.
If your growing non-columnars and prefer a more natural look to your cacti and are patient the free cactus magazine Xerophilia did their first special issue, a small book really, on just that issue. Its a good read if you like non-columnars to look authentic. Its 3/4 the way down that page.

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[misplant]

What properties should a soil have that suits most cacti?

from my 35+ years of experience most cacti will grow in any soil, from 100% sand to hard pan clay and everything in between, including composted organic mixes.

rather than trying to wrap your mind around a specific soil make up, consider a plants watering needs.

factor in your particular growing conditions: indoor, outdoor, relative humidity, annual rainfall, intended watering schedule,  etc.

soil?  what soil.....  these people are growing cacti with hydroponics

http://www.shaman-australis.com/forum/index.php?showtopic=40655

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