Moth orchid

The moth orchid grows on tree trunks and branches across tropical Asia and northern Australia, clinging on with thick roots that are exposed to the air and take up rain as it runs past. Nothing about it is designed for a pot of soil, which is why every mistake people make with it is a soil habit applied to a plant that has never grown in any. Once you understand that you are watering bark and roots rather than compost, it becomes one of the easier flowering houseplants, and it will flower for months at a time.

Light

Bright indirect light, and no direct sun through glass. An east facing window is close to ideal, or a couple of metres back from a brighter one. The leaves are the gauge: a mid green leaf means the light is right, a dark glossy green means there is not enough, and a yellowish or reddish tinge means it is getting too much.

Light is also the usual answer when a healthy plant refuses to flower. A moth orchid in a dim corner will keep its leaves for years and never spike.

Water

Water by the roots, not by the day. The plant is sold in a clear pot for a reason: the spongy layer around each root is silver white when dry and turns green within seconds of getting wet, so you can see exactly when it needs a drink. Take the pot to the sink, run water through the bark for half a minute, let it drain completely, and put it back. In a warm room that comes out at roughly weekly in summer and every ten to fourteen days in winter.

Two habits kill more orchids than anything else. The first is leaving the pot standing in water, which rots the roots within weeks. The second is watering into the crown, the tight point where the leaves meet, where trapped water turns into a soft brown rot that takes the growing point with it. Tip the plant sideways after watering and let the crown drain.

Feeding and repotting

Feed weakly and often: a quarter strength orchid feed every second watering while the plant is in leaf, and a flush of plain water once a month to wash out the salts that build up in bark. Stop feeding while it is in flower if the flowers are what you want to keep, because feed pushes leaf growth.

Repot every two years, after flowering, into fresh coarse bark. Old bark breaks down into something that holds water, and that is when a plant that has been fine for two years suddenly loses its roots. Cut away anything soft or brown while it is out of the pot, and use a pot only just big enough for the root ball.

After flowering

When the last flower drops, look at the stem. If it is still green and firm, cut it back to just above the second visible node from the base and there is a fair chance it will branch and flower again within a couple of months. If it has gone brown and dry, cut it out at the base and let the plant put its energy into a new leaf instead. A moth orchid usually makes one or two new leaves a year and flowers from the axil of a recent one, so a plant that is growing leaves is a plant that will flower.

Ailments

Wrinkled leaves on an orchid nearly always mean lost roots rather than lost water, so check the pot before you reach for the watering can. Silver roots mean thirst, brown mush means rot. Failure to flower is light or the absence of a cool autumn spell. The ledger below covers the rest.