Gadenin日本語Get the appStart by deciding which of three things it is
Nearly every complaint about this plant falls into one of three categories, and they need completely different responses. Working out which one you have, before you treat anything, saves months.
Feel the mix and look at the base of the stalks first, then look at the undersides of the leaves and the joints where stalk meets stalk. That takes a minute and answers the question most of the time.
| What you see | Most likely cause | First move |
|---|---|---|
| Sticky leaves, sooty black film | Scale or mealybug above the sticky patch | Search the leaf joints and stalk undersides |
| Fine pale speckling, dull leaves, faint webbing | Spider mites | Raise humidity and wash the undersides |
| Yellowing lower leaves, soft stalk bases | Root rot from overwatering | Unpot and inspect the roots now |
| Small new leaves, long leaning stalks | Not enough light | Move it to direct sun gradually |
| Brown crisp leaf edges only | Salts or dry air, cosmetic | Flush the pot, trim the edges |
| Leaves split along the veins | Normal, by design | Nothing at all |
The vein splitting is the single most common false alarm with this plant. Large leaves tear into strips as they age and in wind. It is how the plant is built and needs no action.
Scale insects hide in the joints
Scale is the classic pest here and it is easy to miss for months. The adults are brown or fawn oval bumps a few millimeters across, sitting tight against the stalk, in the V where leaf stalks overlap, and along the midrib on the underside of the leaf. They do not look like insects, which is exactly the problem.
The first sign most people notice is stickiness on the leaves below, or on the floor. That is honeydew, and a black sooty mold grows on it. If you find the sticky patch, the insects are somewhere above it.
- Search with a torch Go over every leaf joint, the underside of every midrib and both sides of the stalks with a bright light. Scale that has already been treated stays stuck on, so check whether the bumps come off cleanly.
- Scrape them off physically Wipe them away with a cloth or an old toothbrush dipped in soapy water. On a plant with a dozen leaves this is genuinely the most effective treatment there is.
- Follow up with horticultural oil Spray thoroughly with horticultural oil or insecticidal soap, wetting every joint and leaf underside. Repeat every seven to ten days for at least three rounds to catch the crawlers as they hatch.
- Isolate the plant Move it away from other houseplants until three treatments have passed without new scale. Crawlers walk to neighbors and start the whole thing again.
Check the plant thoroughly before you carry it back indoors in autumn. A summer outdoors is when it picks up scale, and a warm house with no predators is where the infestation explodes.
Spider mites in dry warm rooms
Mites arrive in heated rooms in winter and on plants kept in still, dry air. They are barely visible, so what you notice first is a dull, faintly stippled look to the leaf, as though someone dusted it with pale sand. Fine webbing between the stalk and the leaf base confirms it.
- Hold a white sheet under a leaf Tap the leaf sharply over a piece of white paper. Moving specks the size of dust grains are mites. This is the only reliable way to confirm without a lens.
- Wash the undersides Take the plant to a shower or hose it outside and spray upward at the leaf undersides. Physical removal knocks the population down immediately and costs nothing.
- Raise the humidity Mites thrive in dry air. Grouping plants, standing the pot on a wet gravel tray or running a humidifier makes the room much less suitable for them.
- Treat repeatedly Insecticidal soap or horticultural oil, covering leaf undersides completely, every five to seven days for three or four rounds. One treatment never clears mites, because eggs survive it.
Root rot, and when to give up on a fan
Root rot is the thing that actually kills these plants, and it is a watering and temperature problem rather than a disease you catch. Cold plus wet is the combination. It develops out of sight and is well advanced by the time leaves respond.
The test is at the base. Squeeze the bottom of a leaf stalk where it enters the mix. Firm and solid is healthy. Soft, slightly hollow or wet feeling means the rot has reached that fan.
- Unpot and look Slide the plant out and examine the roots. Firm and pale is good. Brown and soft, with the outer skin sliding off when you pull, is dead.
- Cut back to clean tissue Remove every rotten root and any fan whose base is soft, cutting into the rhizome until the cut surface is firm and white. Use a clean blade and wipe it between cuts.
- Dry the cuts before repotting Leave the plant in a shaded airy place for a day so the cuts callus. Then repot into fresh free draining mix in a pot no bigger than the remaining roots need.
- Water sparingly afterwards Keep it barely moist and warm for a month, with no feeding. A plant with reduced roots cannot use much water and re rotting is the usual second failure.
A plant that has lost most of its top can still recover from a sound rhizome. Do not discard it until the following summer has passed with no new growth.
Leaf spots and lesser troubles
Fungal leaf spotting shows as small dark or gray spots, sometimes with a yellow halo, and appears on plants kept in still damp air or wetted overhead in the evening. It is rarely serious and almost always a symptom of the growing conditions rather than a plant that needs spraying.
| Problem | What causes it | What to do |
|---|---|---|
| Dark spots with yellow halos | Fungal spotting in still damp air | Remove affected leaves, improve air movement, water at the base |
| Fungus gnats around the pot | Permanently damp surface mix | Let the top inches dry, top dress with grit |
| White crust on the mix surface | Fertilizer and hard water salts | Scrape it off, flush the pot, top dress |
| Mealybug, white fluff in the joints | Warm still indoor air | Dab with alcohol on a cotton bud, then treat like scale |
| Whole leaf pale and bleached | Sudden move into full sun | Shade it and acclimate gradually next time |
Write down what you found and when
Pests on this plant are seasonal and repetitive. Scale usually shows up in the months after it comes indoors, and mites in the depths of the heating season. If you note the date you first spotted each one, and which treatment you used, you will know the following year exactly when to start inspecting rather than waiting to be surprised.
Worth noting too: which fan a problem started in, and the date of any rot surgery. If rot recurs in the same part of the clump, that side of the pot is holding water and the answer is the mix or the drainage, not more treatment.