Soil for Cactus

Choosing the proper soil for Cactus and Succulents is very easy, I will cover DIY soil mixing, bagged mixes, and finally amending those mixes from your local garden center. First, lets consider what we want from our cactus mix:

1) Very fast draining

2) Very little compacting

You can do a quick test by dampening the soil and grabbing a handful and squeezing it tightly in your fist. If it stays in a ball when you let go it needs more inorganic matter such as pumice, perlite, or grit. If it crumbles when you open your fist that is what we want for superb drainage and little compaction.

Mixing your own soil for your plants is a bit more work than buying bagged soil but its still very easy. Generally you mix an organic medium such as peat or coco coir with an inorganic medium such as perlite or pumice. Depending on what type of plant the ratio fluctuates. For Trichocereus pachanoi and other more arguably tropical cactus (for lack of a better term) the ratio of 3/2 organic/inorganic is well suited to keep them fed and growing. Desert Cactus such as Cylindropuntia bigelovii need very little nutrients so the ratio is opposite 3/2 inorganic/organic. I also utilize worm castings in small amounts as a source of Nitrogen.

Bagged mixes are generally safe bets as long as they are listed for 'Cactus and Succulents' specifically. Impossible to tell until you buy it and open the bag, but avoid mixes that appear too rich (meaning it has very little inorganics, such as pumice), and avoid mixes that have lots of wood chips. 

The last tip is buying bagged mix whether its standard potting soil, or cactus mix that is too rich and needs amending. In my opinion this method is very effective and much easier than mixing soil from scratch. All I do is put the bagged mix into a wheelbarrow and add perlite or pumice until i achieve the mix I want, using the soil squeezing method I mentioned above.