Pumice (scoria to our European friends) is the king or porosity/drainage soil amendments, but can be expensive, or unavailable in parts of the world. Perlite is a good substitute, and is relatively inexpensive. It is light, which makes pots less heavy, but it tends to float and rise to the top of containers. Gravel is also a good drainage amendment. Some folks like coir, some don't. I would stay away from charcoal, and sand compacts, although used in moderation with other materials it can work. Search this forum for "soil mix" and you will find a wealth of information, but no consensus.

There is no perfect mix. How well any work depends on your local growing conditions, watering regime, type of succulents, etc. There are about as many ideas about what makes the 'perfect' mix as there are growers.

In brief, the most common characteristics are:

1. little or no peat.
2. little or no sand, and then only the sharp angled 'builders sand', not smooth beach sand.
3. 75% or more inorganic materials (pumice, gravel, perlite, turface) with particle sizes between 1/8 and 3/8-inch.

Experienced growers usually think commercial Cactus and Succulent mixes are inadequate: too much peat, too water retentive. However, you can start with one of those, and add drainage amendments. I use one that is already 45% pumice as my organic component, 1-2 parts of the commercial mix, and 8-9 parts pumice and/or gravel.

Have fun with it. Try pumice, try perlite, try gravel. Use them one-at-a-time, or all at once. You will hit on some combination that works for you, and maybe you alone ;)

Brad

"Experienced growers usually think commercial Cactus and Succulent mixes are inadequate..."

Only ones sold around here are almost entirely peat with some fine sand added. Not really suitable for anything.

Perlite I do use a lot, except I'm sort of stuck using Miracle Gro perlite which is a bit smaller than I'd like. Also half the bag's typically been smashed by careless stocking people, which doesn't help. Hence, trying to find something a little... chunkier.

The pumice was actually... sort of pricey but not excessively so. I'll give that and the coir a shot. The charcoal was way more than I wanted to pay.

> Pumice (scoria to our European friends)

Could you please expand on that? I have always beleived that pumice and and scoria are different (even if both has volcanic origin), pumice being the smooth, light-weight, grayish type with very small pores, much of it floats on water, and scoria the sharp, heavier (rarely floats), brick red to dark gray stuff with bigger pores.

That is how I understand it, too. I get my soil here in southern California at a location in Ventura county where they fortunately sell lots of different mixes as well as the pure materials as well. I prefer pumice over scoria since it is lighter and larger (but I sort of dislike the white rocks in the final mix as they don't look all that great in pots and often make their way through the surface top dressings). Scoria at this location is a much smaller, heavier reddish-brown rough volcanic rock, that still is a great addition to cactus mixes, but is more costly and somewhat more water-retentive.

Oh, wait. Given tjicken's description, I think I was looking at scoria. The pieces were somewhat large, as well. Is it possible to break it up at all? Not a LOT, obviously, but a lot of my plants are fairly small and in fairly small pots, so...

Scoria is harder and more difficult to crush than pumice. I have tried using a hammer, but small, sharp bits fly around - they can easily puncture the skin. Crushing it slowly is better, but I do not do that anymore, I do not think it is worth the trouble.

Went ahead and got the orchid mix/coir stuff, as well as the volcanic rock, since it was cheap. It looks like scoria except it's pretty soft. It breaks apart fairly easy just from stepping on it, and it's more of a crumbling sort of breakage and less a... sharp bits flying off thing.

Anyway, both seem a bit too large for use with the smallest plants, but seem like they should be okay for anything that I could put in a slightly larger pot.

Went ahead an potted an unidentified cactus in... I'm guessing about half perlite, a quarter mystery volcanic rock, and a quarter of the orchid bark. This isn't really exact, but I was trying to go with the 75% inorganic thing. If anything perlite was less than half because it weight the least out of everything else and kept settling to the bottom of the container I was mixing stuff up in.

I'd love to get some turface since I've heard very good things about it but I'm almost entirely positive that's not sold anywhere near here.

Anyway, here's a bit of a follow up question, since I'm looking for something for the smaller plants. Perlite's cheap and plentiful. Is there any kind of upper limit on how much of the potting mix could safely be perlite? Or, perhaps, growing things in just straight up, pure perlite?

There are three problems with perlite:

1. It does not contain much nutrients.

2. It crumbles to dust over time.

3. It floats on water and blows off easily, making it difficult to keep in the pot.

In other words: I do not recommend growing in pure perlite.

(I use perlite almost exclusively for my epiphytic cacti, mixed with a lot of other things)

I guess I use the term pumice liberally, and should call what I use scoria. I googled these terms, and found that scoria is a form of basaltic rock, formed in volcanic magma bombs spit out at high velocity. It is red or black, and can have large and small pores, or vesicles. Crushed scoria is sometimes called 'cinders'. It does not float. The pumice folks use for polishing nails is volcanic foam or froth and is chemically different than scoria, more like glass than stone. It has microscopic pores and floats.

Scoria is sold locally as 'volcanic rock'. It is red, and sells for $4 per cubic foot (28 liters) at a landscape supply places. It is virtually identical to the white 'pumice' in 4 liter bags for $2 and OSH and Home Depot. That is probably bleached and washed scoria. It does not float and has large and small pores. It crushes more easily that than red stuff. Geologist place pumice and scoria as points on a continuam. One merges into the other. Perhaps I should not call the volcanic rock I use pumice, even though the white stuff is sold as pumice. Both it and the red volcanic rock are more like 'scoria' than 'pumice'.

Brad

I just checked and found that the white 'pumice' does indeed float, so maybe it really is pumice. :)

amccour,
You might also want to check out an unexpected soil amendment, namely Napa (yes, the auto parts store) Oil Absorbent #8822. It has been used for a long time by bonsai growers, and more recently by C&S growers. It's diatomaceous earth particles.

I no longer use perlite or pumice, for the reasons mentioned above. 8822 is much better, in that it lightens & aerates the soil, but doesn't float to the top like perlite, and slowly releases moisture. It does need to be washed first to remove the "fines." And it's consistent from bag to bag, so I've been able to settle on it as part of my standard mix.

-R