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Nearly every problem on this plant announces itself in the leaves, and the trouble is that opposite causes can look similar at a glance. A soft leaf can mean the plant is dry or that it has no roots left. A dropped leaf can be normal ageing at the bottom of the stem or the first sign of stem rot higher up. The distinguishing detail is almost always where on the plant it is happening, and whether the compost is wet or dry.
Take the habit of running your eye over the plant whenever you pass it, checking three things: the color and firmness of the lowest leaves, whether anything white and cottony is tucked into the leaf axils, and whether the compost is still damp from the last watering. Those three cover most of what can go wrong.
| What you see | Likely cause | Action |
|---|---|---|
| Lowest two or three leaves soft and shriveling, rest firm | Normal ageing, the plant is recycling them | Nothing. Remove them when they come away easily |
| Whole rosette soft, compost bone dry | Genuinely underwatered | Full soak, and shorten the interval a little |
| Whole rosette soft, compost still damp | Root rot | Unpot immediately, cut back to firm tissue, dry, repot |
| Leaf swollen and glassy, then split lengthwise | Heavy watering after a long dry spell | Stop watering, and rehydrate gradually next time |
| Black or brown soft patch on the stem | Stem rot, usually from water sitting at the base | Behead well above the damage and reroot the top |
| Pale bleached patches becoming brown sunken scars | Sunburn after a sudden move into full sun | Shade it and harden it off gradually next season |
| White cottony specks in the leaf joints | Mealybugs | Treat immediately, see below |
| Shiny green patch where the powder is gone | Farina rubbed off by handling | Nothing can restore it. Handle by the pot from now on |
Rot is the one that kills
Rot on a pachyphytum starts either at the roots or at the stem base, and by the time the rosette looks wrong it is already well established. The cause is almost always the same combination: compost that stays damp for too long, in a pot too large, often in cool weather or still air. Cold and wet together is the fastest route to a dead plant.
If you suspect it, unpot the plant at once. This is not something to watch for a week. Healthy roots are pale, firm and stringy. Rotted roots are brown or black, hollow, and pull away as mush. Cut back into clean firm tissue with sterilized snips, wiping the blades between cuts, and if the rot has run up into the stem keep cutting upward until the cross-section is uniformly pale and solid.
If a healthy cross-section exists below the rosette, you have a cutting and the plant is saveable. Dry it for a week and root it as a cutting. If the rot has already reached the base of the rosette itself, take the leaves off the sound part of the plant and propagate those instead. Discard the rest and do not reuse the compost.
Preventing it is entirely a matter of the pot and the mix. A shallow pot barely wider than the plant, a compost at least half mineral, a top-dressing of grit keeping the stem base dry, and air moving past the plant will between them remove nearly all of the risk without you having to be careful about anything else.
Mealybugs, root mealybugs and fungus gnats
Mealybugs are the pest that matters. They look like small specks of white cotton and they hide exactly where you cannot see them, deep in the leaf axils and at the center of the rosette, feeding on sap and leaving a sticky residue that goes sooty and black. On a tightly packed pachyphytum rosette they are easy to miss until there are many, and the powdery farina makes them harder still to spot.
Deal with them on sight. Touch each one with a cotton bud dipped in rubbing alcohol, which kills it on contact, and go over the whole plant including under the lowest leaves. Repeat every five to seven days for a month, because eggs hatch in waves. A heavy infestation is best handled by unpotting the plant, washing the roots, cutting off anything badly infested and repotting into fresh compost in a clean pot. Isolate the plant from your others while you work on it.
Root mealybugs are the same insect below ground and are found only when you unpot, as white waxy deposits among the roots that look like mold. Wash all compost off the roots, discard the compost and the pot or scrub it thoroughly, and repot into fresh mix.
Fungus gnats are harmless to the plant but are a useful signal. Small flies rising from the compost mean the surface is staying damp far longer than it should for this species, which usually means the mix is too organic or the pot is too big. Fixing the drainage removes the gnats and removes the rot risk at the same time.
| Pest or symptom | Where to look | Treatment | Repeat |
|---|---|---|---|
| Mealybugs | Leaf axils, rosette center, under lower leaves | Cotton bud with rubbing alcohol on each insect | Every 5 to 7 days for a month |
| Root mealybugs | Among the roots, visible only when unpotted | Wash roots bare, new compost, clean pot | Check again at the next repot |
| Fungus gnats | Flying up from the compost surface | Let the compost dry fully, add a grit top-dressing | Reassess the mix and pot size |
| Aphids | On flower stalks in spring | Rinse off with a jet of water aimed away from the leaves | Weekly while the plant is in flower |
Damage that is permanent, and worth accepting
Some of what looks like a problem is cosmetic and cannot be undone, and knowing which is which saves a lot of pointless intervention. A fingerprint in the farina is permanent for the life of that leaf. So is a sunburn scar, a split, and a scratch. None of these spread, none of them threaten the plant, and none of them will heal.
The plant deals with them itself by growing. New leaves emerge from the center of the rosette fully coated and unmarked, and the marked ones gradually work their way down the stem and are shed. A plant that has had a bad summer usually looks entirely respectable a year later, provided the light is strong enough for it to keep producing leaves.
So do not attempt to clean, polish or wipe damaged leaves, and do not remove a scarred leaf that is still firm, because the plant is still using the water in it. Take leaves off only once they are soft, shriveled and come away with a gentle sideways rock.
Keep a short record of what went wrong and when
Problems on this plant repeat annually because their causes are seasonal. Rot arrives in the cool damp part of the year, sunburn arrives when plants go outside in spring, mealybugs build up over a warm summer, and splitting follows the first heavy watering after a long dry spell.
Note the date you first saw each one, which plant and which shelf, and what you did about it. After one full year those dates form a pattern you can act on in advance: stop watering earlier in autumn, harden off in stages next spring, check the leaf axils in midsummer before the population builds. That is far more useful than any general rule, because it is measured in your own conditions.