Gadenin日本語Get the appBright shade, not sun, and not a dark corner
In the wild a phalaenopsis grows attached to a tree trunk under the canopy, where it gets bright, dappled, filtered light all day and direct sun almost never. Indoors, the equivalent is a spot close to a window that never gets more than an hour of direct beam on the leaves. An east-facing window with the plant right on the sill is close to ideal. A north window works and is the safest choice, though growth is slower. A south or west window works only if the plant is set back a few feet or the glass has a net curtain or blind between the sun and the leaves.
The mistake in the other direction is just as common. Moth orchids are so tolerant of dim rooms that people put them on a bookshelf across the room from the window, where they sit alive but static for years and never flower. Light drops off far faster than your eye suggests as you move away from glass. If you cannot comfortably read small print in that spot on a dull day without a lamp, the plant is not getting enough.
Wipe the leaves with a damp cloth every few weeks and clean the window glass in winter. Dust on both cuts a surprising amount of light out of an already marginal position.
| Position | Suitability | What to watch for |
|---|---|---|
| East window, on the sill | Ideal | Gentle morning sun is fine, and welcome in winter |
| North window, on the sill | Good and safe | Slow but steady, may flower a little later |
| South or west, 3 ft (1 m) back | Good | Move closer in winter, further back in summer |
| South or west, on the sill, unshaded | Too bright | Scorched patches, yellow bleached leaves |
| Interior wall, more than 8 ft (2.5 m) from a window | Too dark | Dark floppy leaves, no spikes for years |
| Under a grow light, 12 in (30 cm) above | Works well | Run 12 hours a day, keep the fixture cool |
The leaves tell you whether the light is right
You do not need a light meter. A moth orchid getting the right amount of light has leaves the color of a mid-green olive, held out at a slight angle, firm and slightly leathery. That is the target.
Leaves that are dark, glossy, forest green and floppy mean too little light. The plant has increased its chlorophyll to make the most of what it gets, and it will keep growing leaves and refuse to spike. Move it a few feet closer to the window and give it a season.
Leaves that are pale yellow-green, or reddish, or that have dry pale bleached patches with a papery center, mean too much. Sunburn on a moth orchid appears within a day or two of the first hot afternoon of the season, often after someone moved the plant or opened a blind, and the damaged patch never heals; it just stays as a scar for the two or three years that leaf lives. Move the plant back or add a sheer curtain.
A faint reddish or purple tinge on the edges or undersides of the leaves is not always a problem. Many moth orchids show a little of it at the top of their comfortable light range, and a plant in that state often flowers well. Bleached patches and yellowing are the signals to act on.
Steady warmth for most of the year
For growing and flowering, a moth orchid wants ordinary comfortable room temperature: roughly 68 to 80F (20 to 27C) by day and no lower than about 60F (16C) at night for most of the year. It is one of the few orchids genuinely suited to a normal living room, which is why it became the houseplant it is.
Below about 55F (13C) for any length of time outside the deliberate cool spell described below, growth stops and the roots become vulnerable to rot because they are sitting wet and cold. Below 50F (10C) leaf damage starts. Above about 90F (32C), buds abort and flowers fade quickly, and the plant needs far more air movement to cope.
Air movement matters more than most people expect. In still, stagnant air, a damp crown does not dry and fungal spots spread. A ceiling fan on low, or a small fan running gently on the other side of the room, does more for a collection of moth orchids than any amount of misting. What the plant does not want is a cold draft blowing directly on it from an opened window in winter, or the hot dry blast of a radiator or heating vent, which will shrivel buds within days.
Never leave a moth orchid on a windowsill behind a closed curtain on a frosty night. The air trapped between curtain and glass can fall 15F (8C) below the room, which is enough to chill buds and mark leaves.
The cool nights that trigger a new spike
This is the part that decides whether your plant ever flowers again, and it is the part most often missed. A phalaenopsis initiates a new flower spike in response to a drop in night temperature. It needs roughly two to four weeks of nights at about 55 to 60F (13 to 16C), with days still warm at around 75F (24C), before the plant switches from making leaves to making a spike. A difference of at least 10 to 15F (6 to 8C) between day and night is the signal.
This is why a plant kept in a steadily warm room, heated to the same 72F (22C) day and night all year, grows beautiful leaves and never reflowers. Nothing is wrong with it. It has simply never been told that the season changed. Central heating and thermostats remove exactly the cue the plant evolved to read.
Arranging it is easy. In autumn, once outdoor nights are dropping, move the plant to the coolest bright room you have, or simply to a windowsill in an unheated bedroom or a porch, and let it sit through the cool nights for three or four weeks. Alternatively, if you have somewhere sheltered and shaded outdoors that stays above 55F (13C) at night, standing the plant out there through late summer and early autumn does the same job.
Watch for the spike rather than counting days. A new flower spike emerges from between two lower leaves as a blunt, flattened, mitten-shaped green tip that grows outwards and upwards. A new root, which is what people usually mistake it for, emerges rounder in cross-section, points down or straight out, and has a smooth glossy tip. Once you can see a spike an inch (2.5 cm) long, the job is done and you can move the plant back into normal warmth.
Moving the plant through the year
A moth orchid is not a plant you leave in one spot forever. A position that is perfect in midwinter, when the sun is low and weak, may scorch the leaves in early summer when the same window gets three hours of hot afternoon beam. Two moves a year is usually enough: closer to the glass as the days shorten, further back or behind a curtain as they lengthen.
When the spike is in bud, stop moving it. Buds orient themselves to the light source as they develop, and a plant turned round halfway through will open its flowers facing in two different directions. Worse, an abrupt change of temperature, light or humidity while buds are swelling causes them to yellow and drop. Choose the spot where the plant will flower before the buds form, and leave it there until the last flower fades.
Once in flower, you can move a moth orchid anywhere you like to enjoy it, including a dim corner, for a few weeks. The flowers last just as long, and a plant in bloom is doing little growing. Put it back in good light as soon as the flowers are over.
What to write down
Note the position each plant is in and the date you move it, along with a rough note of what light that spot gets: morning sun until ten, or bright shade all day. When one plant on your windowsill flowers reliably and another two feet away never does, that record is the only thing that will tell you why.
Above all, record the cool spell. Write down the date you moved the plant somewhere cooler, the lowest night temperature you saw, how long it stayed there, and the date the spike tip first appeared. Most plants show the spike four to eight weeks after the cool nights start. Once you have that interval measured on your own plant, you can plan next year backwards from when you want flowers, and you stop guessing about the one variable that actually controls reblooming.