One mix does not fit four genera: building substrate by root type
Succulent mixes are usually sold as a single product, but a Haworthia and a Kalanchoe want opposite substrates. The determining factor is not the genus name — it is what the root system is built to do.
Three root types, three substrates
Type A, fibrous and fine (Echeveria, Sedum, Kalanchoe): dense, shallow, fast-growing roots that want to stay in contact with moisture for days at a time. Use 2 parts pumice, 1 part akadama, 1 part coco coir by volume, all in the 3–6 mm range, with up to 20 % of a loam-based compost for nutrient holding.
Type B, thick and contractile (Haworthia, Gasteria, Aloe): permanent, water-storing roots that must never sit in fines. Use equal parts pumice, akadama and granite grit at 2–5 mm and no organic component at all.
Type C, tuberous or storage-rooted (Adromischus, some Pachypodium, Lithops): a single swollen structure that holds weeks of water and rots in a saturated column. Use 4 parts pumice to 1 part akadama and 1 part loam at 2–4 mm, in a pot no deeper than the root mass plus 3 cm.
Particle size matters more than the recipe
A 2 mm particle holds water in the pore space between grains at a capillary tension of roughly 30 cm of water column; a 6 mm particle holds almost none and cannot wick upward effectively. That is why a mix described as gritty can still drown a plant if all the grit is 2 mm.
For most rosette succulents the working distribution is: 40 % at 3–5 mm, 40 % at 5–8 mm, 20 % at 1–3 mm. The smallest fraction provides the water reserve, the largest provides the air-filled pores that roots need at night.
Top dressing: what it does and does not do
A 5–8 mm grit top dressing keeps leaves off wet mix, stops perlite floating to the surface, and reduces fungus gnat activity. It does not reduce evaporation as much as people assume — a 1 cm layer cuts water loss by roughly 15 %, not by half.
Do not use a top dressing on Lithops or on any plant where you need to judge substrate moisture by eye. For those, leave the mix surface visible so you can see the colour change from dark to pale as it dries.
Repotting into a new mix: the three-week transition
When moving a plant from a peat-based commercial mix into a mineral one, the root system must be allowed to adapt. Bareroot the plant, remove all the old mix with a soft brush, and repot into slightly dry mineral mix. Do not water for seven days.
Then water lightly, 25 % of the normal volume, and increase by 25 % each week for three weeks. Root hairs that developed in a moist peat environment collapse if they are suddenly surrounded by dry grit; the graduated schedule is what prevents the plant from stalling for a whole season.
| Month | State | What the plant wants |
|---|---|---|
| January | Growth | Deepest rest. Water only if the lowest leaf ring softens; keep the room as bright as you can. |
| February | Growth | Late rest. Daylight is returning — begin adding an hour of supplementary light every two weeks. |
| March | Growth | Repotting window opens for summer growers. Trim roots, refresh the mineral fraction, dry for a week. |
| April | Growth | Growth restarts. First full watering at the rim, then resume the published interval. |
| May | Growth | Peak growth and the offset season. Feed at quarter strength every third watering. |
| June | Growth | Lengthening days, rising heat. Watch the leaf turgor test rather than the calendar. |
| July | Growth | Hottest weeks. Water in the evening, a third of the spring volume, and only on a visible symptom. |
| August | Growth | Heat eases at night. Prepare mix and pots for the autumn repotting window. |
| September | Growth | Autumn window for winter growers. Root-prune and repot while the soil is still warm. |
| October | Growth | Peak autumn growth. This is the season when most colour work should be done. |
| November | Growth | Daylight falls fast. Taper watering by a quarter and stop feeding entirely. |
| December | Growth | Slow, dry and bright. This is the colour peak for most genera in the collection. |
Tinted rows are the months this genus is genuinely out of action: no repotting, no feeding, and water only if the plant visibly shrinks.
Four things to take away
- Build by root type, not genus: fibrous, contractile, or tuberous.
- Particle size distribution beats the recipe — 40/40/20 across 3–8 mm.
- A top dressing cuts evaporation by about 15 %, not by half.
- Transition to a mineral mix over three weeks, starting with 25 % water.
Informational only — This page is a cultivation record, not horticultural or plant-pathology advice. Any treatment should follow the product label and local regulation.