Gadenin日本語Get the appWhen it actually needs repotting
These are slow, undemanding plants and they are perfectly happy slightly pot-bound. Repot every two to three years, or when there is a clear reason: roots out of the drainage holes, water running straight through a solid mass of root, compost that has broken down to something dark and water-retentive, a plant that has become top heavy enough to tip, or compost you suspect after a bout of rot.
Do it in the warm growing months, ideally in spring once new growth has begun. Disturbed roots need warmth to repair. A plant repotted as the season turns cold sits in fresh damp compost it cannot use, and that is a straightforward recipe for base rot over winter.
| Sign | Action | Urgency |
|---|---|---|
| Roots out of the drainage holes | Repot next warm spell | Routine |
| Water runs straight through | Repot with fresh mix | Routine |
| Compost dark, dense and slow to dry | Repot and coarsen the mix | Do it this season |
| Plant tips over easily | Move to a heavier pot, same size | Safety issue, do it soon |
| Soft or brown at the stem base | Unpot now, cut back, do not repot into old mix | Same day |
| White powder on the roots | Wash the roots, fresh mix, clean pot | Soon |
Set up so you never have to grab the stem
Most repotting accidents with these plants happen at the moment the plant comes out of the pot, when it sticks, someone pulls on the column, and a branch snaps and sprays latex. Plan the lift so your hands are never the thing taking the weight of a thorny stem.
Gloves, long sleeves and eye protection go on first. For anything above about a foot tall, wrap the stem in several folds of newspaper or a thick towel and hold the wrapping rather than the plant, or make a sling from a strip of folded cloth passed around the base. Keep cold water within reach throughout, because if anything does snap you want to seal it within seconds.
- Let the compost dry out first Do not water for one to two weeks beforehand. Dry compost falls away from the roots cleanly, and a dry plant bleeds less if you nick it.
- Free the pot rather than pulling the plant Squeeze a plastic pot all round, or run a long knife between compost and pot wall. If it still resists, break the pot. A broken pot is cheaper than a snapped branch.
- Lift with a wrap or a sling Take the weight through folded newspaper, a towel or a cloth strap around the base. Never grip a thorny column with your fingers, even gloved.
- Check the roots and the base Firm pale roots and a hard woody base are fine. Crumble away only the loose old compost, leaving the core intact. Trim off any black hollow roots with a clean blade and rinse the cut with cold water.
- Pot into dry gritty mix Set the plant at the same depth it was before, never deeper, and firm dry mix around it. Burying the stem an inch lower to make it stand up straight is the single most reliable way to cause base rot.
- Stake it and leave it dry Support a tall plant with a cane and a soft tie so it cannot rock. Then do not water for one to two weeks, and keep it out of direct sun in a warm airy spot while it settles.
If a branch does break, rinse both wounds with cold water immediately until the white flow stops, blot dry, and keep the plant out of strong sun for a week. Save the broken piece as a cutting.
Pot and mix
Go up one size only, an inch or two (3 to 5 cm) wider than the old pot. A big pot holds a large volume of compost the small root system cannot dry out, and permanently damp compost around the base is the exact condition that kills these plants. Depth matters less than width; these are not deep-rooted plants.
Terracotta is the safer choice because it breathes and dries faster, and its weight steadies a top-heavy column. Plastic works if you are disciplined about watering, but plastic plus a heavy mix plus a cool room is a bad combination. Whatever you use, it must have drainage holes, and it should never sit in a saucer of water.
The mix should be gritty and open: roughly half cactus compost and half coarse grit, pumice or perlite, so it drains in seconds and dries through within a week in the growing season. Peat-heavy general compost holds far too much water. A gravel mulch on the surface keeps the very base of the stem dry and makes it easier to see when the surface has dried.
| Component | Proportion | Purpose |
|---|---|---|
| Cactus or succulent compost | About half | Structure and a little nutrition |
| Coarse grit, pumice or perlite | About half | Fast drainage and air around the roots |
| Gravel top dressing | A thin surface layer | Keeps the stem base dry, shows when the surface dries |
| Peat-based all-purpose potting mix | None | Holds water far too long |
Keep a repotting record
Write down the date, the pot size you moved up to, the mix you used, and the height of the plant on the day. Note the date you gave the first water afterwards as well. These plants change so slowly that without notes you genuinely cannot recall whether a pot was refreshed two years ago or five.
The record also tells you something useful about your own conditions: if a plant put on very little height in the two years after a repot, either the light or the mix is wrong, and comparing notes across several plants usually shows which. Add a line for anything you found at the roots, such as mealybugs or rotted sections, so you know which plants to check first next time.