Let's review. This is a sample of cactus mix from the California Cactus Center:iann wrote:Pumice is rock. CEC is virtually zero. Porous is not the same as CEC, which measures how well a substance holds nutrients (without water!) in a form available to plants. Degrading to release trace elements is not the same as holding nutrients for roots. Clay holds nutrients available for the roots and most organic materials hold even more. Most other things hold virtually none and you need to provide the nutrients in soluble form or there aren't any.
That CCC soil mix obviously has some fibres in it, but I can't tell what they are. And something that looks like pumice or perlite, but it seems too dark for perlite. There are plenty of experienced succulent growers and sellers that use (and sell!) awful soils. The cost difference can be compelling, not least because fluffy organic soils are so light while rocks and dirt are so heavy. Loam soils are easy to find but locating a consistent source in commercial quantities not so easy. It also seems like regulations in the US right now make it difficult to bag and sell anything that would be considered a good quality loam.
Now, the dirt in my yard comes from Los Angeles (southwest of downtown), and it supports generally good plant life in the area. For example, my vegetable garden thrives on squash, tomatoes, and peppers (gotta love those Jalapenos and Habaneros!). Obviously, the dirt on its own will not provide sufficient drainage for cacti. So what I'm thinking is this: 50% soil from the yard, 25% gravel (perhaps pea gravel?), and 25% pumice. For Astrophytums, Turbinicarpi, a Cephalocereus senilis, and a Melocactus matanzus, it may be advisable to adjust the ratio more in favor of pumice.
This is only a rough idea at this point, so if I'm going in basically the right direction, I would greatly appreciate any suggestions on the best mix ratios I'd be using. If it turns out that my own mix would in fact be a better replacement for the CCC cactus mix, then I'll start afresh at the beginning of spring.
Thanks!
Steve