Gadenin日本語Get the appBrown leaf edges: the commonest complaint by far
If a coffee plant is going to disappoint you, this is how. A thin dry brown rim appears along the outline of the leaves, sometimes with a narrow yellow band inside it, and it spreads slowly through the winter. It has three causes and they very often occur together, which is why one fix on its own often fails to stop it.
The first is dry air. Central heating pulls indoor humidity down to 25 or 30 percent and coffee expects 50 or more. The second is cold: below about 55F (13C) the roots stop taking up water properly and the leaf margins, furthest from the stem, dry out first. The third is salt, either from fertilizer building up in the compost over several years or from very hard tap water. Work out which by looking at where the damage is worst and what changed.
| Pattern | Likely cause | What to do |
|---|---|---|
| Thin dry rim on many leaves, worst near a radiator | Dry air | Humidifier or grouping. Move it off the heat path |
| Browning on the lowest, oldest leaves in winter | Cold at pot level | Check with a thermometer at the pot. Move off the cold window |
| Browning plus white crust on the compost | Fertilizer salts | Leach the pot, then feed at half strength |
| Brown tips only, after a wilt | Went too dry once | Water more attentively. The damage will not reverse |
| Bleached dry patches in the middle of a leaf | Sun scorch | Move it out of the direct beam |
Damaged leaf tissue never turns green again. Judge whether a fix worked by whether the leaves that open after it stay clean, not by whether the old damage improves. Take a photo when you make the change so you can tell which leaves are which in two months.
Yellow leaves, and what the pattern tells you
Coffee yellows for several different reasons and the pattern is diagnostic, so it is worth looking carefully before treating. Note whether it is the old leaves or the new ones, and whether the veins have stayed green while the tissue between them has gone yellow.
| What is yellow | Cause | Response |
|---|---|---|
| Lowest leaves, whole leaf, soft, dropping | Overwatering or poor drainage | Let it dry down. Check the roots if it continues |
| Oldest leaves, gradual, plant otherwise fine | Nitrogen shortage or exhausted compost | Feed in the growing season, repot in spring |
| New leaves yellow with green veins | Iron shortage, usually because the compost is too alkaline | Use an ericaceous feed or a sequestered iron tonic. Repot into acidic mix |
| One or two old leaves now and then | Normal ageing | Nothing. Remove them when they loosen |
| Sudden yellow and drop after a move | Shock from a change in light or temperature | Leave it alone and keep conditions steady for a month |
The pests that actually turn up
Indoors, coffee gets sap-suckers and effectively nothing else. All of them sit on the undersides of the leaves and in the leaf joints, so a plant can carry a serious infestation for weeks while looking almost normal from above. Turn a few leaves over every time you water and you will catch all of these early, when they are trivial to deal with.
The single greatest risk is a plant that has spent the summer outdoors. Inspect it thoroughly and hose it down before it comes back through the door, because pests that were held in check outside by predators multiply unchecked in a warm dry room.
| Pest | How to recognize it | Treatment |
|---|---|---|
| Scale insect | Brown limpet-like bumps on stems and leaf veins, sticky honeydew below | Scrape off by hand, then horticultural oil or soap every week for a month |
| Mealybug | White cottony fluff in the leaf joints and where branches meet the stem | Dab each one with a cotton bud dipped in alcohol, then treat the whole plant |
| Spider mite | Fine pale speckling on the upper surface, faint webbing underneath | Raise the humidity, rinse the undersides hard, repeat weekly |
| Fungus gnat | Small black flies running on the compost surface | Let the top inch dry between waterings. A symptom of watering, not a real pest |
| Thrips | Silvery streaks and tiny black specks on the leaf, distorted new growth | Isolate, remove worst leaves, sticky traps and repeat soap treatment |
Sticky leaves or a shiny film on the floor under the plant means scale or mealybug, even if you cannot see the insects. That stickiness is honeydew, and it is often the first thing you notice. Look along the undersides of the veins and in the branch joints.
Leaf drop and the difference between panic and patience
Coffee sheds leaves in response to almost any sharp change, and the timing tells you whether to act. Leaves dropping within a week or two of a move, a repot or a change of room is shock, and the right response is to keep everything steady and wait, because interventions at that point usually add a second shock to the first.
Leaf drop with no change behind it is different, and it means something is wrong at the roots or in the air. Check the compost first, then the temperature at pot level, then the undersides of the remaining leaves. A plant that has dropped half its leaves but still has a firm green stem will regrow, often from buds low on the trunk, provided you fix the cause and resist the urge to water it more.
- Check the compost before anything else Put a finger in. Wet and heavy days after watering, with soft yellow leaves dropping, means root problems. Bone dry and light, with crisp leaves, means drought. These need opposite treatments so do not guess.
- Measure the temperature where the plant stands Not the room, the pot. A window sill on a cold clear night can be fifteen degrees below the room average, and that alone will strip leaves off a coffee plant over a fortnight.
- Turn over ten leaves Look along the veins and in the joints with good light. Spider mite and early scale are almost invisible until you look properly at the undersides.
- Then stop changing things Once you have fixed the one cause you found, leave the plant alone for a month in a steady position. Coffee recovers slowly, and moving it repeatedly while you wait is what turns a recoverable plant into a dead one.