Gadenin日本語Get the appBright indirect light, not the sun you assume
Coffee is grown commercially under shade trees on tropical hillsides, and a young plant in the wild spends its whole life in dappled light under a canopy. That is the light your plant is built for. People hear the word coffee, think of a plantation in full tropical sun, and put the pot in the hottest south window in the house. The leaves go pale and yellow-green within a fortnight, then develop dry bleached patches in the middle of the blade that never green up again.
What it wants is a position that is bright all day but out of the direct beam for most of it. A few feet back from a large window, or right in an east window that gets an hour or two of gentle morning sun, is close to ideal. If you stand where the plant stands at midday and look up at the window, you should see a large patch of open sky without the sun itself being in it.
| Position | What it gives | Verdict |
|---|---|---|
| East window, close to the glass | Soft morning sun, bright the rest of the day | The best position in most homes |
| South or west window, three to six feet back | Very bright, no direct beam | Excellent, and the easiest to arrange |
| South or west window, against the glass | Hours of direct midday sun | Scorches the leaves. Move it back or add a sheer curtain |
| North window | Even light, low intensity | Survives, but growth is slow and leggy |
| Interior corner away from any window | Too little for new growth | It will hold its leaves for months and then thin out |
Scorch and hunger look different. Sun damage is bleached, dry and papery in the middle of the leaf where the light struck it. Too little light gives whole leaves that are a uniform dull dark green, on long bare stem between the pairs.
Warm, and never below the mid fifties
The comfortable band is 65 to 80F (18 to 27C), which is the temperature of an ordinary heated room, so for most of the year this looks after itself. The number that matters is the bottom end. Below about 55F (13C) the plant stops taking up water properly and the leaf edges and tips turn brown, starting on the oldest leaves at the bottom. Below 41F (5C) the damage is fast and often fatal, and it does not have to freeze for the plant to be killed.
Cold damage almost never comes from the room average. It comes from one cold spot: the gap between the pot and a single-glazed window on a clear night, the draft off a door that opens onto the street, an unheated conservatory that is pleasant at four in the afternoon and near freezing by dawn. Put a cheap min-max thermometer at pot level for a week in the coldest part of the year and you will find out what the plant is actually experiencing rather than what the room thermostat says.
| Temperature at pot level | What the plant does |
|---|---|
| 65 to 80F (18 to 27C) | Steady growth, deep glossy green leaves |
| 59 to 65F (15 to 18C) | Growth slows and stops. No harm done |
| Below 55F (13C) | Leaf tips and edges brown. Roots stop drinking |
| Below 41F (5C) | Whole leaves blacken and drop within days |
Dry air is the other cause of brown edges
The two things that brown a coffee plant's leaf edges are cold and dry air, and in a heated house in winter you usually have both at once. Central heating regularly drops indoor humidity to 25 or 30 percent, and coffee is a plant of humid forest floors that expects 50 percent or more. The symptom is a thin dry brown rim following the whole outline of the leaf, sometimes with a narrow yellow band just inside it, worst on the leaves nearest a radiator or a heating vent.
The fix that works is a humidifier running near the plant in the heating season, or a group of plants standing together so they hold a pocket of moist air between them. A tray of pebbles with water in it helps a little. Misting looks like it should help and does almost nothing, because the effect lasts the few minutes it takes the water to evaporate. What you can do for free is move the plant out of the path of moving dry air, which is often worth more than anything you add.
- Get it away from the heat source Nothing directly above a radiator, in front of a warm air vent, or beside a wood stove. The moving hot air pulls water out of the leaf faster than the roots can replace it, and that is what kills the edge tissue.
- Group your plants Three or four pots standing within a foot of each other measurably raise the humidity in the air between them. It costs nothing and it looks better than a pebble tray.
- Run a humidifier in the heating season Aim for 50 to 60 percent in the plant's corner. This is the single change that stops new leaves browning, and you will see the difference on the growth that comes after you start, not on the leaves already damaged.
- Leave damaged edges alone Brown edge tissue does not turn green again. Only cut a leaf off if more than about half of it has gone. A leaf with a brown rim still feeds the plant.
Moving it outside for the summer, and bringing it back
A coffee plant enjoys a summer outdoors in a shaded spot, and it will put on more growth in three warm months outside than in a year indoors. The risk is entirely in the two moves. Take a plant from an indoor window straight into open daylight and it will scorch badly in a single afternoon, even in a position you would call shady, because outdoor shade is several times brighter than a bright room.
Coming back in matters just as much, and most people leave it too late. Bring the plant in while nights are still comfortably in the sixties, not when the first cold snap is forecast. A plant that has already had two or three nights at 50F (10C) comes indoors with damage that will surface as browning and leaf drop weeks later, and you will blame the indoor position for it.
- Go out after nights are reliably above 60F (15C) There is no advantage in being early. A cold night outside costs you more than a few extra weeks of growth gains you.
- Two weeks in full shade first Start it under dense shade, on the north side of a wall or under a table on a patio. Then let it have gentle early morning sun only. Never midday sun at any point in the summer.
- Expect to water far more often Outdoors in wind and warmth a pot can dry in two days that would have taken ten indoors. Check it daily rather than keeping to the indoor interval.
- Come back in while nights are still in the sixties Check the undersides of the leaves for scale and spider mite before it crosses the threshold, and hose the whole plant down. Pests brought in from outside spread through a houseplant collection in weeks.
Write down in your records the date you put it out, the date you brought it in, and the lowest night temperature you saw in between. After two seasons you will know your own safe window better than any general advice, because it depends on your garden and not on your climate zone.