Debra's Simple Soil Formula for Growing Succulents
Please don't stress over soil. I've seen succulents thriving in pots filled with garden soil so hard a ball would bounce on it, and at a nursery in soil so rich in peat that moss grew along the edges.
Every grower, nurseryman and collector has a preferred mix. (See a list on page 218 of Succulent Container Gardens, "Potting Mixes: What the Experts Use.") Here's mine. Feel free to modify it based on your climate and growing conditions.
For fat succulents like cactus, euphorbias and pachyphytums: One part bagged soil to two parts pumice.
For thin-leaved succulents like dainty sedums and others that don't store much moisture: Two parts bagged soil to one part pumice.
If that's too complicated or you're doing only a few plants, just buy bagged "cactus mix."
NOTE: I used to tell people to buy "Dry Stall," a product that's basically pumice, at tack and feed stores. Something called "Stall Dry" is NOT the same. If Dry Stall is no longer available, simply obtain "horticultural pumice" at your garden center or online.
No other soil amendment is as widely used by succulent growers and collectors as pumice (crushed lava rock). Here’s why.
- Pumice enhances drainage in garden beds.
- It absorbs excess moisture (is used for that purpose in horse stalls) so roots don’t rot in wet weather.
- It’s a natural, unprocessed organic product that comes from mines.
- It holds onto moisture. Although pumice may appear bone dry, compared to composted pine bark---a major component of bagged potting soils---it retains moisture up to 48 hours (in cool weather). Bark holds moisture about half as long.
- It releases moisture slowly, and at a steady rate.
- Tiny pores on the surface act as microscopic reservoirs to store moisture and nutrients.
- It helps to aerate the soil. (Plant roots need oxygen.)
- Depending on the mine it comes from, pumice may enrich soil with 70 or more beneficial trace minerals.
- It doesn’t decompose, rot or blow away.
Pumice comes in grains that range from 1/8 to 3/8 inches. I use a mix of all sizes, but it doesn't really matter. When in doubt (and if you have the option) go with finer grains for succulents in containers and larger grains for garden beds.
How to Use Pumice in Your Garden
For succulents and other plants that can’t sit in wet soil, improve drainage by amending beds with a mix of 25% garden soil, 25% pumice, 25% compost and 25% sharp (large-grain) sand such as decomposed granite.
Plant cactus and cactus-like plants that store moisture and that are exceptionally prone to rotting (such as fat euphorbias) in berms amended 50% with pumice. If amending the soil in a garden bed isn't an option, fill the planting hole with pumice so roots are surrounded by it, and so the crown of the plant doesn't touch soil.
Use pumice as a topdressing to absorb rainwater that puddles around plants. For succulents and other plants endangered by soft, soggy soil, use a metal bar or broom handle to circle the plant with vertical tunnels (air holes) several feet deep. Space them 12-18 inches apart and about that far from the base of the plant. (The goal is to add pumice to the soil but not to damage roots.) Widen the openings at soil level a bit to make it easier to funnel pumice into them.
How to use pumice in pots
It depends on the needs of individual plants, but for most succulents, simply mix half-and-half pumice with any inexpensive, bagged potting soil. For fine leaved succulents: two parts potting soil to one part pumice; for cacti and rotund euphorbias, the reverse (one part potting soil to two parts pumice). Growers often start rot-prone cuttings and offsets in pure pumice.
Other uses for pumice
Top-dress pots with it before adding crushed glass or florist’s marbles, so that the glass colors stay “true.” In my garden, I top-dressed my faux lily pond with pumice before adding crushed, tumbled blue-green glass and flat marbles.
Cover spilled oil, grease, coolant, hydraulic fluid and other toxic liquids with a layer of pumice. After it absorbs the fluid, sweep it up and dispose of it in an environmentally friendly way.
Where to get pumice
1. Your local feed store
Ask the closest if they carry “Dry Stall.” Dry Stall is pumice in 40-lb bags. Confusion alert: Do NOT substitute a product called "Stall Dry."
2. Garden centers and nurseries
Not all carry "horticultural pumice," and those that do sell small bags at a premium. However, if you're near San Diego, Waterwise Botanicals sells 50-lb. bags (1.5 cubic yards) for under $20.
3. Online (By Mail)
This mining operation sells large quantities primarily wholesale. Their retail cost is a bit pricey, but shipping is included.
Amazon's prices are comparable to those of General Pumice.
Contact sales manager Boyd Reese: Boyd@beaverpumice.com.
What else works?
Crushed lava rock: Used for ornamental purposes, it's available from landscape material (rock) yards and online bonsai suppliers. Smaller is better (1/4"). If not bagged, take your own 5-gallon bucket/s. Garden centers and nurseries also may carry it.
Perlite: Some growers swear by perlite to lighten soils and enhance aeration. For years it was the industry standard. It’s the white bits in potting mixes. Perlite is inert and inorganic, floats to the surface of pots, and in the garden may make tidal drifts of white after watering.
What experts use: Everyone's different. Find various recipes for potting mixes in my book, Succulent Container Gardens, p. 218.
Soil for Succulent Pots and Gardens: How to Select the Best (3:13) - A large succulent nursery's time-tested soil formulas ensure best performance in pots and garden beds.
Soil Mix for Succulents (2:50) In this earlier video, I refer to "Dry Stall," a product that's basically pumice. NOTE: This is NOT the same as "Stall Dry." If your local feed store no longer carries Dry Stall, obtain "horticultural pumice" at a garden center or online.