A reader asked about the soil I use with my cactus and succulents the other day, and I casually responded that I mix compost dirt and perlite. Later I realized that really wasn’t a very helpful answer! I suspect he is not the only person who grapples with that question, and it’s a good question. The planting medium can make the difference in a healthy plant and one that dies a slow wet death or dries up and withers away.
I even asked that question myself in the early days of my cactus adventures and have quietly eavesdropped when the big boys got into discussions of the best soil recipes for their plants, and I will tell you that for every expert you ask, you will get a different answer. It all depends on where they live, the climate and weather they deal with, what materials are easily available to them, and what has worked well through trial and error. So I can give you some general guidelines and share with you what has worked for me, and if all else fails, you can hustle down to a big box store and buy a bag of manufactured cactus potting medium which will probably get the job done. And realize that some species do well with one mixture while others need something with a different balance of ingredients. for example, you might use more gravel when planting some cactus; more dirt with some succulents. So you do have do know something about the plant you are dealing with.
In general cactus and succulents need porous soil that lets the roots develop and allows for good drainage so the roots don’t sit in soil that takes too long to dry out. Cactus and succulents need to be thoroughly watered so that the shallow roots as well as the deeper roots get water, and then they need to be left alone to dry out completely, or almost completely before watering again.I get many questions about spraying or misting the plants. If you do that none of the roots never really get any water and they die, which means eventually the plant will die. I have mentioned in other blogs that a good way to check if the plant is still wet is to stick a thin bamboo shish-kabob skewer down into the dirt and if it comes back wet, wait to water. If no soil sticks to it, water.
My basic recipe is composted dirt and perlite with the occasional addition of decomposed granite, a little pea gravel, and/or sometimes a bit of sand. I’ll admit I don’t follow all the rules for composting, but really, composting is pretty simple. Mix leaves, grass cuttings, cotton burrs, horse or cattle manure, food scraps from the kitchen, water and turn it as much as you can, be patient, and you will have an ongoing supply of good rich dirt. I have tried composting worms in the past as they can speed up the process, but the poor little worms don’t do well in a raised container in our very hot, arid climate, so as they disappear I don’t replace them very often. With our limited rainfall I have to regularly wet it down with the hose, and unfortunately that schedule is sort of hit and miss, but it still makes good dirt over time. But the pile does need water for the decomposing process to work.
I add perlite for more drainage when mixing the soil for use. Do not add vermiculite, which is intended to retain water and works well for foliage plants, but not for cactus. In the beginning, I mixed dirt, vermiculite and perlite and rotted many plants. I was told very bluntly by a nurseryman in Arizona that I was mixing a recipe for disaster, so I quit the vermiculite. And he was right; plants did much better without it. I now buy perlite in large bags so I don’t have to constantly run to the store for yet another small bag when I run out. You may not need it in bulk, but that works for me. You might notice four of my ten rain barrels in the background. Cactus do like rainwater; only problem with that is we don’t get much rain! But when it does rain, the barrels do fill up, and I try not to waste it when watering.
I am not real scientific when I mix the two ingredients; it probably comes out to about 75% compost dirt and 25% perlite with decomposed granite and pea gravel thrown in now and then, depending on the needs of the plant being planted. And sometimes a little sand makes it into the mix. But don’t use straight sand as It tends to pack and the roots don’t like it.
I buy 80-pound bags of the granite when I am visiting in the Texas Hill Country because it is readily available down there. I sometimes use it in the mix, but the main thing I use it for is as top-dressing to hold the dirt in place when watering and to complete the look of the potted cactus or dish garden. It really finishes off your creation. It is available in a variety of colors and sizes.
I have heard of using crushed pumice, but that is not as available for me, so I don’t worry about it. I know some growers who use a 50-50 mix of perlite and dirt, nothing but the pumice, and other endless variations. Many pre-mixed soils and additives are available as well. I checked the ingredients of manufactured cactus potting soil and found they use a similar mix for what they call a fast-draining formula: processed forest products (whatever that means), sphagnum peat moss (which I don’t like because when it dries out it never reabsorbs water well), sand, perlite, a light fertilizer, and a wetting agent. So even they use the things I have talked about. No matter what dirt you wind up using, fertilizing is a good idea, maybe more so with succulents than cactus, but they all like a little boost now and then, especially as blooming time comes around. A basic plant food will work but you can also find specific cactus and succulent plant food that is good. And plain old water lightly mixed in can be your wetting agent, but dry soil works, too.
I haven’t bought potting soil in years and have had good luck with my recipe. Experiment and find out what works for you. Good luck!