After all my reading, I’ve been learning a lot about soil for succulents, and wanted to share what I’ve learned. Most of this involves the soil, but there’s a bit about container choices as well.
If you do much reading at all, you’re going to find a lot of people talking about their “recipes” for soil, and everyone has a different one. So here’s the basics of what I’ve learned:
- Rule #1: Commercial mixes are generally not very good.
A basic potting soil, even the ones that are branded for cacti and succulents, are not that great on their own. They can be a good start, but need help. What you want to focus on is how much organic content your soil has, and commercial mixes tend to be primarily peat, and in much too high concentrations. You’re going to be experimenting with mixing in lots of things — mostly perlite, vermiculite, gravel, coarse sand (small pebbles), crushed granite (available as chicken grit), fired clay, pumice, etc.
- Rule #2: Your best recipe is going to be your own – and it will take some experimentation.
It will depend on the atmosphere where your plant will live (How hot is it? How humid? How much air circulation is there?) and what kind of pot your plant is in (is it clay or plastic? Will it breathe and absorb water?) Organic content will hold moisture longer, and the more your the general situation is suited to retaining moisture, the less organic content you’ll want. You’ll know you have a good mixture by wetting it and holding it in your hand. If it crumbles instead of clumps, you’re off to a good start.
- Rule #3: When making a mix, pay attention to particle size.
You want all your materials to be approximately the same size of grain. Those roots need air as well as water, and grain size is very important for this! The goal of creating your mix is really about creating a light soil that doesn’t mat around the roots, but rather contains a lot of small air pockets. Mixed sizes will have more tendency to “settle in” — as will extremely fine sand (such as play sand). When you water the plant, you are filling in those pockets – and as the soil drains, the retreating water pulls air down into the soil behind it. (Hence, whenever I water my plants, I listen for a quiet “snap crackle and pop”. That sound is a very good sign.)
- Rule #4: Peat is the most readily available, but should be your last choice for organic content.
It’s light and easy to ship, which makes it a favorite for use with commercial mixes, but peat has a few qualities that make it not great for succulents. When it thoroughly dries out (which you want your succulents to do in between watering), it has a tendency to repel water when moistened again. If you’re watering slowly, you’ll see the water bead up on top before it slowly starts absorbing. Alternative options include coconut coir or shredded bark. (Peat has also been getting frowned upon for being a resource that’s not easily renewable. Coconut coir and shredded bark are viewed as being more ecofriendly, although the process used to turn coconut fiber into coir for potting is somewhat controversial when it comes to being “ecofriendly”.) All that being said, coconut coir is getting easier and easier to find – big box stores around here are most likely to carry it in bags as “organic seed starting mix”, or in a compressed brick form. Just be careful to get it from a reputable dealer or brand, as some coconut coir is processed or cured with chemicals or salts that can be harmful for your plants. Bark based mixes are usually branded or marketed for bonzais. Peat also will break down over time and become more dense, which prevents air from getting to your roots.
- Rule #5: The non-organic content for your mix should be chosen carefully.
You don’t want to use too much in the way of “heavy” stone particles. Pumice, vermiculite and perlite are good, because they’re porous and light weight. A bit of travelling through forums will find several good posts explaining the difference, and each has its own strengths and weaknesses. Vermiculite holds water a lot longer, and breaks down faster. That makes it good for rooting cuttings and tropical plants, but maybe not as good for succulents. Perlite is light and cheap, but dusty and a bit a messy. (I’ve also found perlite more prone to moss and fungus growth if it’s exposed to still air for seed starting and rooting cuttings.) Perlite still holds a bit more water than pumice, but is cheaper and lighter. In places where pumice isn’t readily available, many folks are using crushed granite (which is usually sold at farm and agriculture centers as “chicken grit”) as a cheaper alternative.
- Rule #6: Low organic content means you’ll want to fertilize more frequently in the main growing seasons.
Find a fertilizer than has low nitrogen (given that succulents don’t grow a lot of greenery), and use it at a more diluted strength to what’s recommended on the label – half strength or lower. Succulents can be slow growers, and you don’t want to build up more chemicals in the soil than will be used. You can fight that by “flushing” the soil when you water your plants; succulents are damaged by the frequency of watering more than the volume. When you do water, you will want to thoroughly moisten until water runs out of the bottom, and then wait for the soil to thoroughly dry out before watering again. Ideally, it wouldn’t take very long for the soil to dry out. Moisture shouldn’t be hanging out in the pot for long periods of time.
- Rule #7: You’ll need to replace the soil periodically.
Those commercial mixes of potting soil are recommended to be changed every year or two as the peat breaks down and the soil starts to mat around the roots, preventing air flow to the roots and increasing moisture retention; adding amendments like perlite and vermiculite will extend the usability of the mixture, but doesn’t avoid it completely. This rule generally applies to all container plants, not just succulents.
- Rule #8: Repotting succulents is very different than your average house plants.
You may be used to the rule of thumb being that you want to try to avoid disturbing a plants roots when repotting or planting; but here, you want to remove as much soil from the roots as you can. It’s recommended to clear them off as much as possible, inspect for any rot or soft spots, cut out any that look sick or damaged, and even let the bare roots sit out of the soil for several days to dry out before repotting — especially if you are dividing the plant or making any cuts to remove sick roots. Don’t be afraid to remove roots that look discolored, ill or feel soft and mushy. Succulents have water held in reserve, they cope and adapt to root pruning far better than other plants. Some mesembs, like lithops, actually have a natural cycle where the feeder roots die off back to the central trap root annually on their own when they are dormant. As for letting the root ball dry while exposed, you want the cut to have a chance to callous over before it goes back in the soil to prevent bacterial invasion at the wound. When it’s time to repot, pick a pot that’s only slightly larger than the size of your roots. The plant roots are actively absorbing and wicking moisture from the soil; the more inactive and unused soil you have in your pot, the more soil that’s going to be sitting and holding onto moisture. Many people intentionally root bind some succulents in smaller pots because of this.
- Rule #9: Acquiring your materials probably will require some creativity.
While many common amendments can be found in the gardening section of your big box store, so may require that you go further afield. Searching online will give plenty of advice. If you read much about the “recipes” other folks are using, they frequently will reference the unusual ingredients and where they acquired them. Crushed granite, for instance, is most easily available commercially as “chicken grit” at farm stores near livestock or pet feed. Turface (a fired clay) is also popular.
And for my final rule, I’m breaking away from the topic of pots and soils to talk about light. Succulents do great with neglect when it comes to watering, but require lots of light. Don’t go overboard, though. Small succulents are used to growing in the shade of rocks and other plants, so they typically will want filtered light or indirect light in great quantities. If you’re keeping them indoors under lights, or in a green house with artificial lights, make sure you don’t neglect to give them an artificial night too.
- Rule #10: Succulents need darkness to breathe. Succulents use what’s called crassulacean acid metabolism. The short version is this: they only open up their pores to absorb the carbon dioxide necessary for photosynthesis at night, when it’s dark and cooler. In their natural arid environments, they lose much less of their precious stored moisture this way, rather than opening up their pores in the more intense heat of the daylight hours. Succulents and cacti that are kept in brightly lit and poorly ventilated environments will slowly starve to death if they aren’t given periods of well ventilated (ie: not a closet) darkness.
All right succulent experts – anything you think I’ve missed, overlooked, or gotten wrong? Please comment and share the wealth!