Orchid care: watering, light and reblooming a moth orchid

Light

Orchid low light is not houseplant low light. Clemson describes Phalaenopsis as one of the orchids most adaptable to indoor conditions, thriving at 1,500 to 1,700 foot-candles, while the University of Illinois Extension's houseplant scale calls 75 foot-candles low and 300 bright. So a moth orchid belongs at the window, not across the room. NC State names an east windowsill as the best spot, with well-shaded west or south windows also workable, and the RHS suggests an east- or west-facing sill in winter, when bright light helps the plant produce flower spikes.

Summer sun is the hazard. The RHS warns that direct sun scorches the leaves, and Clemson wants little or no direct sun on the plant. Leaf color works as a light meter: Clemson notes that very dark green leaves mean the light is too low, one of the main reasons orchids fail to flower. Where windows are poor, Clemson says fluorescent tubes 6 to 12 inches above the leaves, run 12 to 16 hours a day, can serve as the only light source.

Water

Clemson calls a waterlogged pot one of the fastest ways to kill an orchid. NC State's method is to water in the morning with tepid water, set the plant in a sink, let water flow freely through the medium, and then let the pot drain completely so it never stands in water. The RHS suggests watering lightly about once a week, and Clemson gives the same weekly rhythm for actively growing orchids, letting the mix dry slightly before the next watering and watering again only when it is nearly dry throughout.

The roots themselves tell you when. The RHS points to pale, silvery roots as the cue to water, and plump green roots mean there is still moisture in the pot. A clear plastic container makes this easy to see, which is one reason NC State and the RHS both recommend one. Never let the roots dry out completely, the RHS says, and never water so often that the bark stays soggy; roots that are brown, mushy or hollow have already rotted.

Keep water out of the crown, the cup where the leaves meet. Clemson warns that water left on the leaves or in the leaf axils can readily lead to disease and death, and watering in the morning, as NC State advises, gives stray drops a full day to dry. After the flowers fade and leaf growth pauses, Clemson suggests cutting back both water and fertilizer until new leaves start.

Soil and pH

Potting soil kills orchids. Clemson is blunt about it: most orchids are epiphytes, and one of the best ways to kill one is to plant it in soil. The RHS adds that loam-based or multipurpose compost will kill moth orchids. Use a bark-based orchid mix; Clemson and UF/IFAS list the usual ingredients as fir bark, chopped tree fern fiber, charcoal, volcanic rock and a little peat. NC State recommends moving plants out of pure sphagnum moss, which is hard to rewet, into bark. The RHS explains why bark has a shelf life: as it decays it becomes denser and holds water longer, so the mix needs complete replacement every couple of years.

Humidity

Clemson puts the humidity orchids need at 40 to 60 percent all year and notes that most homes fall short, so it usually has to be supplemented. NC State describes moth orchids as preferring high humidity. A humidifier nearby, or the wide saucer of damp gravel the RHS suggests, raises the moisture around the leaves, and in hot weather the RHS recommends misting the foliage and aerial roots daily. Keep air moving at the same time; Clemson warns that damp, still air favors bacteria and fungi.

Temperature

Moth orchids like the same warmth people do. The RHS gives 66 to 86°F (19 to 30°C) by day and 61 to 66°F (16 to 19°C) at night, and Clemson sets a minimum night temperature of 65°F for Phalaenopsis. The one deliberate exception is a cool spell to trigger blooms: NC State says the large-flowered white hybrids that bloom in spring need nights around 55°F for a week in autumn to start flower spikes, while modern dwarf hybrids do not. For a healthy plant that has stopped flowering, the RHS suggests a spot about 8°F cooler for a month or so. Keep orchids away from radiators and drafts the rest of the time.

Fertilizer

Feed weakly and often. NC State recommends a balanced fertilizer twice a month at half strength, or weekly at quarter strength. Clemson suggests formulas richer in nitrogen, such as 30-10-10 or 15-5-5, for orchids growing in bark, and an even ratio such as 20-20-20 for those in other media. Flush out salts regularly: Clemson says to rinse the pot with plain water each month, and the RHS suggests skipping the feed every fourth watering. Feed sparingly, if at all, in winter, and remember that UF/IFAS notes too much fertilizer can actually inhibit blooming.

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Repotting

NC State advises repotting about every two years, after the blooms have faded or as new leaves begin to appear; the RHS adds that any time of year works as long as the roots are active and have green tips. The trigger is decayed bark more than a crowded pot. Pull out all the old mix, snip off brown, shriveled, mushy or hollow roots and, as the RHS describes, shorten healthy roots to about 5 inches. If the roots fit the old container, reuse it; a much bigger pot keeps the bark wet. Leave aerial roots in the air, and UF/IFAS advises waiting at least several weeks before fertilizing.

• The bark has broken down, looks like soil and stays wet
• Roots inside the pot are brown, mushy or hollow
• The plant has grown too large for its container

Propagation

Commercial moth orchids are raised in laboratories, and the RHS notes that seed propagation is only possible there. At home, the practical method is the keiki, a small plantlet that sometimes sprouts from a node on the flower stem. The RHS says to wait until it has several good roots, at least about three-quarters of an inch (2 cm) long, then detach it and pot it in orchid mix, watering sparingly at first and misting the leaves daily. Keiki paste dabbed on a node of a spent stem can coax one out after six to eight weeks, the RHS notes, though ordinary rooting hormone will not work.

Methods: Keiki (plantlet) from a flower-stem node, Seed, in a laboratory only · Best season: when a keiki has several roots at least 3/4 inch long.

Common problems

NC State lists scale and mealybugs as the pests to watch, and Clemson adds spider mites and thrips. Bud blast, when buds yellow and drop before opening, comes from changes in temperature, humidity, moisture, fertilizer or location, according to NC State. Shriveled or wrinkled leaves signal a water shortage, either from a medium kept too dry or from roots already rotted by soggy bark. Botrytis can spot the flowers, and Clemson lists leaf spots and bacterial soft rot among common orchid diseases. A plant that never reblooms usually lacks light or fertilizer.

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Is the moth orchid toxic to cats and dogs?

The ASPCA lists the Phalaenopsis orchid, also sold as moth orchid or moon orchid, as non-toxic to cats, dogs and horses, which makes it one of the safest flowering plants to keep where a pet can reach. Non-toxic means no poisoning concern in the ASPCA database, not that the plant makes a good chew toy: bitten leaves and flowers ruin the orchid, and the fertilizers and pest sprays used on it are separate products with their own label warnings. Keep a curious cat away from the plant for the orchid's sake, and if your pet eats something you cannot identify, call your veterinarian or the ASPCA Animal Poison Control Center.

Check any other plant against the ASPCA lists →