Gadenin日本語Get the appWork out which of four things it is
Chinese evergreen has a small and predictable list of problems, and almost every one of them shows up first as marked or discolored leaves. The trouble is that cold damage, root rot, mites and scorch can all look similar from a few feet away, and treating the wrong one wastes weeks while the real cause continues.
Before you reach for anything, do two checks. Put a finger into the compost to find out whether it is wet or dry, and turn a marked leaf over and look at the underside in good light, preferably with a magnifier. Those two pieces of information separate the four causes almost every time.
| What you see | Likely cause | The confirming check |
|---|---|---|
| Gray-green water-soaked patches, then papery tan | Chilling injury | Recent night below 55F (13C) at that spot |
| Lower leaves yellow from the base, stem soft | Root rot | Compost wet, roots black and soft |
| Fine pale stippling, leaves dull, faint webbing | Spider mite | Undersides, with a magnifier |
| Pale bleached patches on the sunlit side | Scorch | Direct sun reaches the plant at some hour |
If the compost is wet and the leaves are limp, stop watering before you do anything else. More water is the wrong answer to almost every symptom this plant produces.
Cold damage, the one people misread
This is the signature problem of the species. Chilling injury begins below about 55F (13C), which is a temperature most people would not think twice about, and the damage appears three to seven days after the cold night that caused it. By then the weather has changed and nobody connects the two.
The pattern is distinctive once you know it. Damage is worst on the leaves nearest the cold source, so a plant on a window sill is marked on the window side and clean on the room side. Patches start gray-green and water-soaked, then either dry to a thin tan papery texture or, in a humid room, turn black and slimy at the leaf base.
- Move it first Get the plant away from the cold source before you do anything cosmetic. Into the room, off the floor, away from the vent or the door. The damage already done cannot be reversed, but it will keep happening otherwise.
- Cut off collapsed tissue Remove any leaf that has gone soft, black or slimy, cutting the whole leaf off at the stalk. Wet dead tissue is where secondary rot gets into the stem. Leave leaves that are only marked, since they still work.
- Keep it dry while it recovers A cold-damaged plant is drinking almost nothing. Water sparingly and only when the compost is properly dry, and do not feed until new growth appears.
- Wait for the new leaves Recovery shows as clean new leaves from the center, usually four to eight weeks after it warms up. If the growing point itself went black, cut back to firm stem and treat the plant as a cutting.
Rot at the roots and the stem base
Root rot is the other major killer and it is almost always caused by watering a cool plant on a warm-season interval. The stems are thick and hold water, so the plant looks fine for weeks after the roots have failed, and then goes over quickly.
The early sign is lower leaves yellowing evenly from the base of the plant upward, several at once, while the compost is wet. Normal ageing takes one leaf at a time and only from the very bottom. If two or three leaves yellow together and the pot is wet, take the plant out and look at the roots the same day.
- Inspect the roots Firm and white or pale tan is healthy. Black, soft, and slipping their outer skin when pulled means rot. Wash the compost off so you can see clearly rather than guessing.
- Cut back to clean tissue Remove every soft root with clean scissors. Press the stem bases: any that are soft or squashy go too, cut up into firm white tissue. Firm tissue can be saved, soft tissue cannot.
- Repot into a smaller pot Fresh free-draining mix, the smallest pot that holds what is left. Do not add fertilizer and do not add a water-retaining amendment. A big pot around few roots repeats the whole failure.
- Water once, then be patient Keep it warm, out of direct sun, and let the surface dry fully between waterings. A plant with half its roots gone still needs less water, not more.
Fungus gnats running over the compost surface are not the disease, but they are a signal. They breed in permanently damp compost, so a gnat problem means the watering is wrong and the roots are at risk.
The pests that actually turn up
Indoors this plant gets a short list of pests, and all of them are far easier to deal with in the first fortnight than in the second month. Check the undersides of two or three leaves whenever you water and you will catch every one of them early.
| Pest | Where to look | What you see | Treatment |
|---|---|---|---|
| Spider mite | Leaf undersides and leaf axils | Fine pale stippling, dull leaves, webbing when heavy | Rinse undersides, then soap or oil weekly for a month |
| Mealybug | Leaf axils and where stems meet the base | White cottony fluff, sticky residue | Dab each one with alcohol on a swab, repeat weekly |
| Scale | Along stems and midribs | Small brown limpet-like bumps that do not brush off | Scrape off by hand, then horticultural oil |
| Fungus gnat | Compost surface and around the pot | Small dark flies running and hopping | Let the compost dry further, use a sand or grit top layer |
Spider mite thrives in warm dry air, so it appears most often in a heated room in winter. Raising humidity and wetting the leaf undersides regularly does much of the control on its own.
Treating without damaging the leaves
The leaves are broad and slightly waxy, and they mark easily. Treatments applied in direct sun or at full strength cause damage that lasts longer than the pest would have.
- Rinse before you spray Take the plant to a sink or shower and rinse the leaf undersides with tepid water. That physically removes most of a mite or mealybug population and makes any spray far more effective.
- Spray out of direct light Apply insecticidal soap or horticultural oil in the evening or in a shaded spot, and let it dry out of the sun. Oil plus direct sun burns the leaf.
- Repeat on a weekly cycle One application never clears mites or mealybugs, because the eggs are unaffected. Treat weekly for four weeks and check the undersides each time before you decide you are done.
- Isolate and check the neighbors Move the affected plant away from the others as soon as you find anything, and inspect everything that stood within arm's reach of it. Mites in particular have usually already moved.
Knowing when to give up on a plant
There is a point at which cutting your losses is right. If more than two thirds of the roots are rotten and the stem base is soft all the way through, the plant will not recover. But before you throw it out, check every stem for a firm section: a single firm piece with one node will reroot in warm compost and rebuild the plant, which is a better outcome than starting over.
Write down what happened and when. The date you first saw the symptom, where the plant was standing, what the room was doing, and what you did about it. Cold damage in particular repeats in the same spot every winter, and a note from last year is what stops you putting the replacement plant in exactly the same place.