John Innes is the UK's traditional loam-based potting compost, standardised in 1934 by the John Innes Horticultural Institution and still sold by garden centres across Britain in four numbered formulations. It works very well for shrubs, fruit trees, and traditional bedding plants. Used straight under most succulents it produces a wet, rich, organic substrate that rots roots and breeds pests. The bottom line is that John Innes No.2 has a real place at 30 to 50 percent of a succulent mix, and almost no place at higher proportions. Here is the rest of the picture.
Part of the Beginner's Guide to Succulents.
What John Innes is
John Innes is not a brand. It is a recipe, in the same sense that "Mediterranean diet" is a recipe rather than a product. The formulation was published by the John Innes Horticultural Institution (a research body originally founded in 1910 in Merton, now based in Norwich and best known for plant genetics work) and entered widespread commercial use after a 1934 publication standardised the proportions and the base fertiliser dose.
The recipe is short. By volume, you take 7 parts sterilised loam, 3 parts peat (which most contemporary manufacturers replace with coconut coir on environmental grounds), and 2 parts coarse horticultural sand. To that base you add a measured dose of John Innes Base, a dry fertiliser blend of Hoof & Horn meal (a slow-release organic nitrogen source), superphosphate (phosphorus), and sulphate of potash (potassium), plus ground chalk to buffer the acidity of the peat. The proportions of base fertiliser are what distinguish the four numbered formulations.
The key physical numbers, the ones that determine how the substrate behaves under a succulent root, are pH 6.0 to 6.8 and water-holding capacity 40 to 60 percent by volume after a thorough soak. That second figure is the one that gets growers in trouble. A pumice-based succulent mix runs 25 to 35 percent water-holding by volume; an akadama-heavy mix sits around 50 to 60 but drains faster because of granule structure. John Innes holds water like a loam, because it is a loam, and a loam is exactly what most succulents did not evolve to grow in.
The four formulations (1, 2, 3, Seed)
Four standard recipes share the same loam-peat-sand base and differ only in fertiliser dose.
| Formulation | Base fertiliser per 36 L | Intended use |
|---|---|---|
| Seed | None (chalk only) | Germination, very young seedlings |
| No.1 | 110 g | Pricked-out seedlings, slow-growing young plants |
| No.2 | 220 g | Established plants, summer bedding, general repotting |
| No.3 | 330 g | Mature plants, heavy feeders, long-term containers |
For succulents the relevant entries are Seed and No.2. The No.3 dose is overkill for almost every succulent in common cultivation, with one or two exceptions noted below. No.1 sits in an awkward middle ground: too rich for most cacti, not rich enough to outperform a leaner mineral seedling mix. Seed compost is occasionally useful for Lithops and Conophytum sowings as a small organic component on the surface, but pure Seed compost holds far too much moisture for direct use under any adult succulent.
Why straight John Innes fails for most succulents
Three failure modes, all mechanism-driven.
The first is moisture. A 13 cm pot of straight John Innes No.2 holds roughly 500 to 600 ml of plant-available water at field capacity. Under an Echeveria or a Crassula in a temperate UK winter, that pot stays wet for two to three weeks between waterings even with the watering can put away. The plant is barely transpiring at 5 to 10 °C, the substrate is not draining out the bottom because there is little air-filled porosity to let it, and the fine roots sit in saturated loam for long enough that anaerobic bacteria establish. The classic outcome is a winter root rot the grower discovers in spring when the rosette pulls cleanly off a black stump.
The second is fertility. Succulents evolved on lean, mineral-poor substrates, often weathered volcanic ash or skeletal limestone. Their nitrogen uptake is slow and their tolerance for excess nitrogen is low. A pot of No.2, and especially No.3, supplies more nitrogen in a single watering cycle than most desert succulents would encounter in a season in habitat. The visible result is etiolated growth: pale, swollen, soft leaves that flop and snap, internodes that stretch instead of staying compact, leaf colour that washes out from red and bronze to flat green. The plant looks worse, and it becomes mechanically fragile and pest-attractive.
The third is biological load. Loam is by definition organic, with 5 to 15 percent organic content by mass even in a sterilised JI mix. Organic content feeds the soil community: fungus gnats lay eggs in the moist surface, root mealybugs (Rhizoecus spp.) breed faster on organic-rich roots, and several common rot fungi (Fusarium, Pythium, Phytophthora) establish more readily where decomposing carbon is available. A fully mineral substrate starves these organisms by default. A loam substrate provides them with a steady food supply.
For the great majority of cacti, Echeveria, Haworthia, Aloe, Mammillaria, Astrophytum, Sedum, and Sempervivum, straight John Innes is the wrong substrate. Cut with mineral aggregate, it can still earn a place. Used neat, it is reliably worse than no organic matter at all.
Where John Innes actually helps
The exceptions are real, and naming them precisely is part of using the recipe well.
The first is leafy, heavier-feeding succulents whose habitat is genuinely not desert. Aeonium species evolved on Mediterranean volcanic soils in the Canary Islands and Madeira, often with significant organic content from leaf litter and bird-deposited nutrients on cliff faces. Aeonium arboreum, Aeonium tabuliforme, and the popular A. 'Zwartkop' all root and grow visibly better in a mix carrying 30 to 50 percent JI No.2 than in pure pumice, because their photosynthetic surface area is large and their nitrogen demand follows.
The second is tree-form succulents that need substrate ballast for stability. Crassula ovata, the jade plant, develops a heavy crown over a slender base and tips over in a light pumice mix once the canopy gets large. A 50 percent JI No.2 fraction adds the bulk density that anchors the root mass and keeps a 5 kg plant upright in a 25 cm pot without needing weighted ceramic. The same applies to Portulacaria afra trained as a bonsai, Cyphostemma caudiciforms grown for display, and large Sedum dendroideum in patio containers.
The third is winter-growing genera that benefit from steady moisture during their active phase. Greenovia aurea, Greenovia diplocycla, and the dormant-summer Aeoniums all push their root activity through cool, damp winter conditions where a pure mineral substrate dries faster than the plant prefers. A 30 to 40 percent JI No.2 fraction in their winter pots provides the moisture buffer their physiology actually wants, with the caveat that the same mix is wrong for their summer dormancy and the plants are best moved to a drier regime when they tighten into their summer rosettes.
The fourth is container hybrids where heavy fruiting or flowering demands sustained nutrients. The newer Echeveria show hybrids with thick, ruffled leaves and frequent inflorescence pushes (E. 'Cubic Frost', E. 'Esther', E. 'Lola') deplete a lean mineral substrate within a season and respond visibly to a 30 to 40 percent JI No.2 fraction with stronger leaf colour and faster offset production. The case for No.3 in a small fraction is narrower still, reserved for monocarpic Agave approaching their bolt: a flowering Agave americana needs an unusual quantity of stored phosphate and potassium to push its 6 m inflorescence, and the No.3 dose is calibrated for exactly that demand profile.
Practical mix recipes
A working set of starting points, all percentages by volume:
- General succulent collection (Aeonium, Crassula, soft-leaved Echeveria, large rosette Sedum): 50 percent John Innes No.2 plus 50 percent pumice. The mix holds enough moisture to support the plants through a UK summer, drains cleanly through the pumice fraction, and keeps the substrate biologically lighter than pure JI.
- Cacti and Mexican Echeveria with thicker, waxy leaves: 30 percent JI No.2 plus 70 percent pumice. The lower JI fraction is the upper limit for most cacti and for the firmer rosette species. Mammillaria, Echinocactus, and Astrophytum still prefer zero JI; this recipe is for the in-between species (E. agavoides, E. peacockii) where a small moisture buffer helps.
- Monocarpic Agave approaching bolt: 10 to 20 percent JI No.3 plus 80 to 90 percent pumice. The No.3 dose meets the inflorescence nutrient demand without saturating the rootball with moisture during the long bolt window.
- Tree-form display jades (C. ovata, P. afra): 50 percent JI No.2 plus 50 percent pumice, with a thicker drainage layer of coarse pumice or lava rock at the base of the pot for ballast and air space.
The 30 to 50 percent maximum is the rule that prevents most failures. Below 30 percent the JI contribution is mostly cosmetic. Above 50 percent the moisture and fertility penalties start to dominate, and you are growing a houseplant in a succulent pot.
The single most reliable cause of "I gave my succulent John Innes and it died" is the British hobby practice of using "JI No.2 plus a bit of grit", which usually means 80 to 90 percent JI with a token 10 to 20 percent grit dressing. That ratio is wrong by a factor of two. The grit, or better the pumice, needs to be at least half the mix by volume, ideally more, and the substrate should feel coarse and gritty in the hand, not loamy.
Substitutes outside the UK
John Innes is not sold internationally under that name; the recipe is a British convention and most growers outside the UK have never encountered it. Useful substitutes are easy to identify by composition.
In continental Europe, Floragard Kakteenerde (a German cactus and succulent compost) and the Lithanic Mineral Mix sold by specialist Dutch and German nurseries both deliver substrates with broadly similar pH, organic content, and water-holding to a JI No.2 cut with pumice at 50:50. Floragard's standard succulent compost is not identical to JI but behaves comparably as a 30 to 50 percent fraction in a mineral mix, and the Lithanic mix arrives pre-cut with mineral aggregate so it can be used closer to neat.
In North America, Espoma Cactus Mix is the closest off-the-shelf equivalent, though it runs a little richer and a little wetter than JI No.2. Cut with extra pumice at a 1:1 to 1:2 ratio (Espoma to pumice), the result mimics a 50 percent JI No.2 succulent blend and works well for Aeonium, Crassula, and the leafy Echeveria hybrids. Bonsai Jack succulent mix, gritty mix from Al's recipe (turface, pine bark, granite chips), and Black Gold Cactus Mix are alternative starting points, each requiring more or less pumice depending on local climate.
The principle, regardless of regional brand, is that the organic component should sit at 30 to 50 percent of the final mix and should be a structurally stable, lightly fertilised loam or coir blend. The mineral component should be pumice, lava rock, or a mix of the two. Anything closer to pure organic compost is the British "JI plus a bit of grit" mistake, dressed in a different bag.
See also
- A Beginner's Guide to Succulents, for the substrate, watering, and light foundation that determines whether John Innes belongs anywhere in your collection.
- DIY substrate mixing, for the ratios and sourcing notes when blending John Innes, pumice, lava rock, and coir into working succulent mixes at home.
- pH of succulent soil, for how the JI pH 6.0 to 6.8 range fits with succulent nutrient uptake and tap-water carbonate buildup.