The short answer
Use a gritty, fast-draining mix, either a bagged cactus and succulent mix or your own blend of equal parts potting mix and pumice or perlite.
Why drainage matters
Ordinary potting soil is made to hold water, and for a succulent it holds far too much. Roots that sit wet rot. Succulents need a mix that drains sharply and dries quickly.
Grit is what gets you there. Pumice, perlite or coarse sand opens the soil up, so water runs straight through, air gets back in, and the pot dries out between drinks. That's what makes the soak-and-dry method work.
Grit can't rescue a pot with no way out, though. Every succulent pot needs a drainage hole. A layer of gravel in the bottom is not a substitute: plants in those pots still tend to stay too wet, and the gravel can even slow drainage.
How to make succulent soil
This is a starting point, not a law. Extension services suggest anything from one part grit to four parts potting mix, up to two parts grit to one part mix. Start in the middle, then adjust.
- Pick a base. Ordinary bagged potting mix is fine. Pine bark, compost or coir also work as the organic part.
- Pick your grit. Pumice, perlite, coarse sand or fine gravel. Any one works, or mix them. If you use sand, make sure it's coarse.
- Mix by volume. Use the same scoop or pot for every part. Equal parts base and grit is a good first batch.
- Test it. Water a pot of it. Water should run straight through, and the mix should feel light and granular, not spongy. If it stays soggy, add more grit.
Ratios to start from
All by volume. Sources don't agree on one perfect ratio, so pick one, then watch how fast your pots dry and adjust.
Everyday, 1 to 1
Equal parts potting mix and pumice or perlite. A sensible middle ground for most potted succulents.
Extra gritty, 1 to 2
One part potting mix to two parts pumice, perlite, coarse sand or fine gravel. The mix Iowa State Extension suggests, and the grittiest of the four.
Three-way, 1 to 1 to 1
Equal thirds potting mix, coarse sand and pumice. A favorite of the UC Master Gardeners in California.
Gentle, 4 to 1
Four parts potting mix to one part pumice, perlite or crushed lava. The least grit any of our sources suggests. If it stays wet, add more.
Buying a bagged mix
A bag is the easy route, and a perfectly good one. Here's what to look for.
The right label
Look for "cactus and succulent" mix. In the UK it's usually sold as cactus compost, and the RHS suggests a peat-free one.
The right feel
It should be light, granular and fast-draining. If it looks and feels like ordinary potting soil, stir in some extra grit.
Fresh, not old
Potting mix breaks down over time and holds more water. Replace it every 2 to 4 years, which is a good excuse to repot.
FAQ
Can I use regular potting soil for succulents?
Not on its own. Regular potting soil holds too much water, which risks root rot. Mix it with grit first. Equal parts potting mix and pumice or perlite is a good start.
Is cactus soil the same as succulent soil?
For practical purposes, yes. Bagged mixes are usually sold as "cactus and succulent" mix and suit both. In the UK, look for cactus compost.
Which is better, perlite or pumice?
Both work, and extension services list them side by side. Use whichever you can find. Coarse sand and fine gravel are fine too.
Does gravel in the bottom of the pot help drainage?
No. It's no substitute for a drainage hole and can actually slow drainage. Mix the grit through the soil instead.
How often should I replace succulent soil?
Every 2 to 4 years, or whenever you repot. Old mix breaks down and holds more water than it used to.