Mixing Your Own Succulent Substrate: Recipe by Genus

Part of the A Beginner's Guide to Succulents: What They Are and How to Keep Them Alive.

Bagged "cactus and succulent" compost from a garden centre is, in most cases, peat-based potting mix with a handful of grit thrown in. It works for a season, then collapses and rots roots. Mixing your own substrate from pumice, lava, sand, and a small organic fraction is the single most consequential change you can make to a succulent collection, more impactful than fertiliser, pot choice, or watering rhythm. Here is the rest of the picture.

I'm Dr. Elena Martín, a Certified Advanced Cactus & Succulent Horticulturist and former curator of the succulent collection at the Jardín Botánico de Córdoba. The recipes below come from twelve years of repotting, filtered down to what continued working after the things that looked good on day one had failed by month six.

Part of the Beginner's Guide to Succulents.

Why mix your own

Three reasons. First, control. A bagged "cactus mix" is opaque about its actual ratio of mineral to organic, and most fail honest scrutiny. A peat-heavy bag with 15 percent perlite is sold under the same label as a pumice-based mix with 90 percent mineral, and you cannot tell from the front of the bag.

Second, cost. A 50 L bag of "cactus and succulent compost" runs 12 to 18 EUR and contains perhaps 5 EUR of mineral aggregate; the remainder is peat and a small grit fraction. Buying pumice, lava grit, and a sack of John Innes No. 2 separately and blending them in a bucket gives you four times the working mineral substrate for the same outlay.

Third, longevity. A mineral-heavy mix holds its structure for five to ten years in a pot. A peat-based bagged mix degrades inside a year, sometimes within months. The plant gets one good summer, then sits in slumped fines while you wonder why it stopped growing.

Ingredients to keep on hand

Six ingredients cover almost every recipe. Buy them in bulk, store them dry, and they will outlast their organic counterparts by a decade.

Pumice 3 to 8 mm is the workhorse. It provides bulk drainage, holds the pore structure of the mix open for years, and grips fine roots without crushing them. A 20 L bag at 15 to 25 EUR will mix six or seven adult-plant pots.
Lava rock 5 to 15 mm is denser and harder than pumice. Use it as the bottom-third ballast in tall pots and as a top-dressing on display work, where its dark colour reads as desert pavement.
Coarse sand 1 to 3 mm plays the role of fine drainage. It fills gaps between larger pumice particles in mixes where you want a tighter pore structure, particularly for fine-rooted Echeveria and small Mesembs. Quarry sand, not beach sand; salt residues from beach sand burn roots within weeks.
Coir or peat-free John Innes is the organic component, used sparingly. Coir blocks are cheap and structurally consistent; John Innes No. 1 (lower fertility) and No. 2 (medium fertility) are loam-based formulas that behave more predictably across batches than the supermarket potting composts they sit beside on the shelf.
Akadama 3 to 8 mm is optional and reserved for moisture-stable mixes. Lithops, Conophytum, seedling Astrophytum, and Madagascan Kalanchoe earn the price premium; most other genera do not.
Horticultural sand 0 to 2 mm is for top-dressing only. Particles below 1 mm clog the pore structure of any mineral mix they are incorporated into, so this grade never goes into the body of the substrate.

The framework (mineral % + structural component + organic %)

The single most useful number when designing a substrate is the total mineral percentage. It defines the wet-dry cycle the plant will experience, and that cycle is what either matches or fights the species' habitat.

Mineral %	Substrate type	What it suits
50%	Standard potting mix	Tropical houseplants, ferns, NOT succulents
70 to 80%	Mediterranean garden	Aeonium, Crassula ovata, Aloe, soft-leaf perennials
80 to 90%	Typical succulent	Most Echeveria, Agave, Aloe, Haworthia
90 to 100%	Cacti and slow-growers	Lithops, Conophytum, mature Mammillaria, Astrophytum

A mix at 50 percent mineral holds water for ten to fourteen days in a typical pot, which is fine for a Monstera and lethal for a Mammillaria. The same pot at 90 percent mineral dries inside three to five days. The plant's biology determines which side of that ledger it belongs on, and the substrate has to match.

The structural component, usually pumice, is what keeps the mineral fraction performing across years. Without it, sand and organic matter compact within a season into something that looks like substrate but functions like wet plaster. With it, the pore structure remains open and the wet-dry cycle stays predictable.

The organic component is the lever you adjust to fine-tune fertility and moisture buffering. Zero organic gives you a true cactus mix; 30 percent gives you a fast-growing Aeonium mix; the gap between is where most succulent genera live.

Recipes by category

These ratios reflect what I run across roughly 400 plants in my own collection. They are starting points, not scripture. Adjust by 5 to 10 percent in either direction based on your watering frequency, light intensity, and pot size.

Cactus mix

90% pumice (3 to 8 mm)
10% coir or fine John Innes No. 1 (low fertility)

For Mammillaria, Echinopsis, Ferocactus, Astrophytum, and the broad column of cacti that want lean, fast-draining substrate. The low fertility matters. Cacti grown in nutrient-rich substrate produce soft, etiolated growth that splits and scars at the first stress.

Soft Echeveria mix

70% pumice (3 to 8 mm)
20% coarse sand (1 to 3 mm)
10% John Innes No. 2

For the run of fleshy Echeveria species and hybrids, including E. elegans, E. agavoides, E. lilacina, and most of the Korean propagation trade. The coarse sand fills gaps between pumice particles and supports the fine root mat without compacting.

Aloe / Agave mix

80% pumice (3 to 8 mm)
10% lava rock (5 to 15 mm)
10% John Innes No. 2

For the broad run of Aloe vera, Aloe aristata, Aloe variegata, Agave attenuata, Agave americana, and similar Mediterranean-climate xerics. The lava rock at the bottom of the pot stabilises top-heavy plants against tipping and adds long-term ballast that pure pumice does not provide.

Madagascan Kalanchoe mix

70% pumice (3 to 8 mm)
20% akadama (3 to 8 mm)
10% coir

For Kalanchoe beharensis, K. tomentosa, K. orgyalis, and other species from the seasonally dry inland habitats of Madagascar. The akadama buffers moisture in a way that matches the conditions these species evolved with; substituting straight pumice tends to produce stunted, leaf-shedding plants that never reach the velvety mature foliage they are grown for.

Lithops / Conophytum mix

95% pumice (3 to 8 mm), OR
50% pumice (3 to 8 mm) + 50% akadama (1 to 4 mm fine grade)
ZERO organic

For Aizoaceae genera that grow in pure mineral grit in their habitat: Lithops, Conophytum, Pleiospilos, Titanopsis. Any organic component invites rot during the resting phase. Top-dress with pure pumice or fine grit so the plant body itself never touches damp substrate.

Aeonium mix

60% pumice (3 to 8 mm)
30% John Innes No. 2
10% sand (1 to 3 mm)

For Aeonium arboreum, A. canariense, A. tabuliforme, and the run of Macaronesian rosette species. Aeonium are summer-dormant and winter-growing in their native Canary Islands climate, and they want more organic matter than other succulent genera. A pure mineral mix produces small, slow rosettes; a 30 percent organic mix produces the loose, leafy crowns these species are grown for.

Sterilisation

A common worry, and largely a non-issue at the home scale.

Pumice and lava rock are inert volcanic materials. They contain no organic matter and no live pathogens, and they do not need sterilising. Rinse them in a colander to wash off fines if the bag arrived dusty; otherwise use them straight.

Coir from new sealed bags is sterile. The processing involves heat and compression that kills pathogens and weed seeds. Once you have opened the bag and used part of it, store the remainder dry and it will stay clean for years.

John Innes from sealed bags is, for practical purposes, "as good as" sterile. The loam fraction is heat-treated during manufacture, and reputable brands ship the bags clean. Avoid loose loam or unprocessed garden soil as substrate ingredients; they carry root mealybugs, fungus gnat eggs, and a long list of soil-borne pathogens.

Sand is the one ingredient that occasionally warrants treatment. Quarry sand can carry calcium carbonate fines that shift pH, and in rare cases it carries plant-pathogenic fungi. For sensitive seedling work, including Lithops germination flats and Conophytum propagation, rinse the sand thoroughly in a colander and then bake it on a tray at 100 °C for 30 minutes. For adult-plant repotting, this step is unnecessary; the substrate dries fast enough that pathogen pressure stays low regardless.

Top-dressing sand or grit does not need sterilising under any circumstance. It sits above the soil surface, dries between waterings, and offers nothing pathogens can colonise.

Storage

Mineral components last indefinitely. A bag of pumice or lava grit stored dry in a garage or shed is as good in ten years as the day it arrived. The only practical risk is moisture absorption from a damp floor; stack bags on a pallet or board to keep their bases off concrete.

Organic components have a real shelf life. Coir blocks store dry for four to five years before they begin to break down structurally. Once expanded with water, use them within a few weeks; rehydrated coir kept damp invites fungal growth. John Innes bags hold their structure for two to three years if kept dry and sealed; after that, the loam fraction tends to slump and the mix loses the open texture you bought it for.

Sand and grit, mineral by definition, last indefinitely. Store them in their original sacks or in clearly labelled buckets with lids. An unlabelled bag of sand is indistinguishable from a bag of fine pumice once the cardboard tag falls off, and confusing 0 to 2 mm horticultural sand with 3 to 8 mm pumice in a recipe is the kind of mistake that costs a tray of seedlings.

A practical inventory for a 50 plant collection: one 20 L bag of 3 to 8 mm pumice, one 10 L bag of 5 to 15 mm lava rock, one 5 L bag of 1 to 3 mm coarse sand, one compressed coir block, and one 10 L bag of John Innes No. 2. Total cost in Europe runs 50 to 70 EUR and will mix substrate for two years of repotting.