Fishtail hoya (Hoya polyneura)

Meet the plant

An epiphyte from the eastern Himalaya, Assam, Tibet and Nepal through Myanmar and Laos to south-central China (Kew POWO), first collected near Darjeeling around 1848 and found mostly high in trees at 1,000 to 3,000 m (Vermont Hoyas, outer variegated). Its leathery leaves are marked with many fine veins slanting from the midrib like the bones of a fish, which gives it both its common name and polyneura, "many veins" (RHS profile, Vermont Hoyas, outer variegated). The leaves hang in pairs from stems that rise and then arch over, so a grown plant is a curtain from a hanging pot (Vermont Hoyas, polyneura).

It is a cool-forest plant, and that shapes everything. It wants bright light without heat, humid air, a chunky mix that drains, cool nights and steady care (Healthy Houseplants, Foliage Factory). Growers find it roots easily and then can go downhill just as quickly, its leaves yellowing and dropping, though a plant that settles can do well for years (Vermont Hoyas, polyneura). Foliage Factory calls it less forgiving of heat, root disturbance and uneven care than the easy hoyas (Foliage Factory). This guide calls it moderate. Much of the detail here comes from growers and nurseries; no extension service has written about this species, so the general hoya advice fills the rest.

No poison-centre list names it; the ASPCA lists its relative the wax plant as non-toxic to cats and dogs (ASPCA), and Foliage Factory calls it generally non-toxic. The milky sap can irritate skin and eyes, so wear gloves when you cut it (RHS growing guide).

You will usually buy a rooted cutting or a small hanging pot. What to expect in a year: in a cool, bright, humid spot, a quick grower, with new pairs through spring and summer and the first strands arching over the rim (Foliage Factory); in a hot or dry room, slower, with some lost leaves along the way.

Light

Bright, indirect light: an east window, or a little way back from a south or west window behind a sheer curtain (Healthy Houseplants). Foliage Factory asks for bright indirect light and protection from hot direct sun (Foliage Factory); Araflora grows it in full light to part sun (Araflora); Vermont Hoyas hangs one in an ordinary window with no extra lights (Vermont Hoyas, outer variegated). The cautious path is bright light with only gentle morning sun, because hot afternoon sun scorches the leaves (Healthy Houseplants) and heat stresses the plant.

Too much sun shows as bleached or brown patches. Too little shows as stretched stems with the pairs far apart, smaller leaves and no flowers (Iowa State Extension, UF/IFAS Gardening Solutions).

Water

Check first. Push a dry finger as far into the mix as it will go, and lift the pot: learn what it weighs wet and dry (Vermont Hoyas, watering, Clemson HGIC). Dry all the way down and light means it is time. Any dampness means wait. The leaves help: soft leaves that hang limper than usual are asking.

The rule: water thoroughly, until it runs out of the bottom, once the mix is almost dry, then let it dry again. Sources differ on how far. Healthy Houseplants waters when the top few centimetres are dry; Foliage Factory waits until the mix is 60 to 80 percent dry; Araflora lets it nearly dry out and warns against waterlogging (Healthy Houseplants, Foliage Factory, Araflora). This guide takes the drier side, because the plant copes with a dry spell far better than with soggy roots (Healthy Houseplants). Water through, not in sips, and empty the saucer (Vermont Hoyas, watering). Healthy Houseplants prefers rainwater or filtered water, or tap water left to stand for a day. Keep the rhythm steady; this plant takes sudden changes badly.

Thirsty: soft, limp leaves, sometimes folding a little, on a dry, light pot. A soak brings them back within a day or two. Overwatered: leaves yellowing and dropping while the mix is still wet, soft dark stems at the base (Vermont Hoyas, polyneura, Iowa State Extension). If the leaves say thirsty and the soil says wet, believe the soil and look at the roots.

How often that lands depends on the pot, the mix, the light and the room. In a hanging pot of chunky mix in bright light in summer it often comes round about once a week, which is what Vermont Hoyas does for a plant in a window (Vermont Hoyas, outer variegated). In winter, with cooler rooms and less light, the mix dries more slowly and waterings space out (Healthy Houseplants, UF/IFAS Gardening Solutions), though dry heated air can empty a pot faster than you expect. Treat the numbers as a reminder to check, not as the instruction.

Soil and pot

A chunky, fast-draining mix that still holds some moisture: roughly equal parts orchid bark, perlite and coir or peat-free compost, with a little charcoal, slightly acid (Healthy Houseplants, Foliage Factory). The general hoya mix of orchid bark, peat-free compost and coarse perlite works too (RHS growing guide). Vermont Hoyas wondered whether a nursery's own potting mix was why one plant did so well (Vermont Hoyas, polyneura): if a bought plant is thriving, there is no hurry to change its mix. Refresh the mix every two years or so as it breaks down.

The pot needs a drainage hole and should be small, usually a hanging one. It tolerates being slightly root-bound, which helps it flower (Healthy Houseplants), and a pot too large keeps the mix wet (Clemson HGIC). When you do move up, go one size, 2 to 4 cm wider (Vermont Hoyas, repotting). Plastic lets you judge the weight and keeps a humid-loving plant from drying too fast.

Repot every two or three years in spring, when roots come out of the hole or the mix has compacted (Healthy Houseplants, Araflora). Disturb the roots as little as you can and do not prune them (Healthy Houseplants). Soak it in, then wait until the new mix is nearly dry before watering again: the first two months are when overwatering does the most harm (Vermont Hoyas, repotting). Hold the feed for several weeks.

Feeding

Very lightly. A balanced liquid feed at a quarter strength every four to six weeks from spring to late summer, tapering off in autumn, and nothing in winter. Healthy Houseplants gives a quarter to half strength on that rhythm, Araflora says it needs little, and Iowa State feeds hoyas at a quarter or half strength (Healthy Houseplants, Araflora, Iowa State Extension). This guide takes the weaker dose. Every few months water through with plain water to wash out salts (RHS growing guide).

Flowering

Clusters of small stars, cream to pale yellow with a dark red centre, sweetly scented in the evening (Healthy Houseplants, Araflora). They drip a lot of sticky nectar, which can stain wooden furniture, so put a cloth under the plant (Araflora, Vermont Hoyas, outer variegated). Sources disagree on season: Healthy Houseplants says late spring through summer, sometimes into early autumn, while Vermont Hoyas saw buds set at many nodes as the days shortened in autumn. Summer into autumn covers both.

What it takes: a plant with established strands, bright indirect light, a slightly root-bound pot, and cool nights (Healthy Houseplants, Araflora). Most hoyas that never bloom are not getting enough light (UF/IFAS Gardening Solutions).

Two things never to do. The flowers come again from the same spurs, so leave them on the plant when the flowers fall (Healthy Houseplants, RHS growing guide). And once buds appear, do not move or turn the plant until the flowers are over; a moved hoya drops its buds (Iowa State Extension).

When something looks wrong

Look at the soil first, then at what changed: this plant answers change with leaves.

• Leaves yellowing and dropping. The classic fishtail complaint (Vermont Hoyas, polyneura). Check the mix first. Then look for a cold draught, a sudden temperature swing, a heater or air-conditioning vent, or a recent move (Healthy Houseplants). Let a wet mix dry almost completely, keep it above 13 C and out of draughts, and keep its spot steady.
• Soft, limp or folding leaves. Check the mix. Dry and light: soak it. Wet: let it dry and slide it out to look at the roots. On a hot day it may be heat; move it out of a hot window (Foliage Factory).
• Black soft base, wilting on wet mix. Root rot from overwatering (Healthy Houseplants). Cut away only the dark soft roots, repot in fresh, barely damp airy mix in a small pot, and take cuttings of healthy strands straight away: a plant this far gone often does not recover (RHS growing guide).
• Brown or black leaf spots. Leaves left wet without airflow (Healthy Houseplants, Iowa State Extension). Water the mix, not the leaves, let air move, remove the worst leaves (Clemson HGIC).
• Scorched patches. Hot afternoon sun (Healthy Houseplants). Move it back or filter the light.
• Leaf edges browning and curling. Dry air. A pebble tray, a humidifier or grouped plants, and distance from the radiator.
• No flowers. Light first, then age, the pot (too large?), the spurs (were they cut?) and warm nights (Araflora).
• Sticky drops in flower. Nectar, plenty of it. Normal. A cloth under the plant, and wipe wood before it stains (Araflora).
• Buds drop before opening. The plant was moved, or the watering or temperature changed suddenly (Iowa State Extension). Leave it where it is.
• Mealybugs. White cottony tufts in the leaf joints (Healthy Houseplants, UF/IFAS Gardening Solutions). Dab each one with a cotton bud in rubbing alcohol, wash with insecticidal soap, repeat weekly, and keep the plant apart until clear (Clemson HGIC).
• Scale. Small hard brown bumps (Healthy Houseplants). Wipe or scrape them off, then wipe with insecticidal soap or horticultural oil and repeat.
• Spider mites. Pale speckling and fine webbing in dry warm air (Clemson HGIC). Shower the plant, undersides included, every few days, spray with insecticidal soap or neem weekly, and raise the humidity.

Propagation

By stem cuttings, which root easily (Vermont Hoyas, polyneura). In spring or summer, take a piece of stem 10 to 15 cm long with two or three nodes, and root it in water or in moist perlite or sphagnum moss; roots usually come in three to six weeks (Healthy Houseplants, Vermont Hoyas, propagation). Keep the cuttings warm and humid under a clear cover, out of direct sun. Wear gloves for the sap. Pot the rooted cutting into the chunky mix in a small pot, and keep its care steady while it settles: the weeks after potting up are when a young fishtail most often falters.