Sweetheart hoya (Hoya kerrii)

Meet the plant

A slow, sturdy climbing vine with thick, fleshy, heart-shaped leaves, each one 5 cm or more across and firm as a slice of apple (RHS profile, NParks). The form in this app, 'Albomarginata', has a cream edge around each green heart. It comes from the forests of South East Asia, from Thailand to southern China, where it climbs trees as an epiphyte. Those thick leaves are its whole character: it stores water for weeks, shrugs off a missed drink, and does badly in a pot that stays wet.

It is the slowest of the common hoyas. NC State rates its growth slow; the RHS gives it five to ten years to reach its full size; the variegated form is slower still because it has less green to work with (NC State Extension, RHS profile, Ohio Tropics). Expect a few new hearts a year, long bare runners before the leaves fill in, and no flowers until it has been with you a while. Growers call it very tough (Vermont Hoyas, kerrii); Iowa State adds that it is more particular about light and humidity than the ordinary wax plant (Iowa State Extension).

One thing to know before anything else. The single heart sold in a small pot around Valentine's Day is usually a leaf cutting with no stem node. It can stay green for years, but it has no growing point and will never make a vine or a flower (Iowa State Extension, NC State Extension). You cannot tell from outside whether a node is there. If you want a plant that grows, buy one that is already vining (Ohio Tropics).

NC State tags it non-toxic to cats and dogs, and the ASPCA lists its close relative the wax plant as non-toxic (NC State Extension, ASPCA), though it has no entry for this species itself. The milky sap can irritate skin, so wear gloves when you cut, and one botanical database lists it as toxic if eaten (UF/IFAS Gardening Solutions, NParks).

Light

As bright as you can give it. Put it right in front of an east, west or south window; a few hours of gentle direct sun suits it once it has been introduced over a couple of weeks (Clemson HGIC, Ohio Tropics). The RHS says bright and shaded from hot sun; Logee's grows it in filtered light; Ohio Tropics wants a few hours of direct sun (RHS profile, Logee's). The cautious path is bright indirect light with morning or evening sun, and a sheer curtain against hot afternoon glass. The variegated form needs the most light of all and is particularly sensitive to overwatering in dim light (Pistils Nursery).

Too much sun turns all the leaves a lighter yellow-green and can scorch them (Ohio Tropics, Iowa State Extension). Too little shows as no growth at all, thin stretched runners, fading cream margins, and no flowers (Clemson HGIC). A north window is not enough.

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 hearts help: a thick leaf that has gone a little thin, soft or puckered is asking (NC State Extension, Pistils Nursery).

The rule: treat it like a succulent. Once the mix has dried out completely, water thoroughly until it runs out of the bottom, then let it dry out completely again (Clemson HGIC, The Houseplant Guru). Water through, never in sips; a splash that wets only the surface leaves the roots dry and the plant thirsty on damp-looking soil (Ohio Tropics). Use room-temperature water (NC State Extension). If an old dry mix sheds water, water it two or three times in a row until it takes.

Thirsty: hearts thinner, softer, puckered, on a dry light pot. A soak brings them back over a few days. Overwatered: leaves yellowing or dropping while the mix is wet, or soft leaves on wet mix, which means the roots have died and can no longer drink (Iowa State Extension). Overwatering is the most common problem and root rot the biggest threat to any hoya (Clemson HGIC); with leaves this thick the plant will forgive a late drink far sooner than an early one.

How often that lands depends on the pot, the mix, the light and the room. In a chunky mix in a bright warm spot in summer it often comes round every couple of weeks, and in winter every three to five weeks or longer. No reputable source gives a number for this species, and one grower waters more in winter because heated air dries the pot, so the numbers are only a reminder to go and check (Vermont Hoyas, watering). Sources agree on winter being drier than summer; they differ on how dry, from "just moist" (RHS profile) to "very sparingly" (UF/IFAS Gardening Solutions). This guide takes the drier side, because it is far easier to overwater when it is cool.

Soil and pot

A chunky, fast-draining mix, because this is an epiphyte and its roots want air: equal parts orchid bark, peat-free compost and coarse perlite or pumice (Clemson HGIC, RHS profile). Growers go chunkier still, mostly perlite and bark with a little compost (Vermont Hoyas, medium). Ordinary potting soil alone stays wet far too long for this plant. Mixes break down over two or three years into fine material that holds water; refresh on that rhythm even if the pot stays the same.

The pot needs a drainage hole and should be snug. It grows and flowers best root-bound, and a pot that does not keep it root-bound holds water the roots cannot use (NC State Extension, NParks, The Houseplant Guru). When you do move up, go one size only, 2 to 5 cm wider (Ohio Tropics, Vermont Hoyas, repotting). Growers disagree on material: several prefer terracotta for its airflow, while Vermont Hoyas warns that bare terracotta dries a chunky mix so fast it kills the fine outer roots and uses glazed or plastic pots. Either works if you check before you water.

Repot rarely, in spring or summer, never in winter or while in bud. The RHS says it dislikes repotting and can stay in the same pot for many years (RHS profile). The two months after a repot are when overwatering does the most harm (Vermont Hoyas, repotting); water with extra care then and hold the feed for a month or so.

Feeding

Lightly. A balanced liquid houseplant or orchid feed at half strength about once a month from spring to early autumn (RHS profile, Iowa State Extension). Nothing in winter. The variegated form needs even less (Ohio Tropics). Sources range from a quarter-strength feed at most waterings to monthly; the weak monthly rule sits inside all of them, and with a plant this slow there is little to gain from more.

Flowering

A grown plant flowers in summer: rounded clusters 4 to 5 cm across of small, furry, cream to white stars with a dark pink to purple-brown centre, scented at night and dripping a reddish-brown nectar that stains, so keep it off the furniture while in bloom (NParks, NC State Extension, Logee's). Sources differ on the colour and on how fragrant it is; the RHS says white with purple centres, NC State pink with red centres, and Iowa State finds it less fragrant than other hoyas (RHS profile, Iowa State Extension).

It is shy to flower when young (NC State Extension), and a single rooted leaf never flowers. What it takes: a vining plant a few years old, the brightest window you have, a snug pot, warmth, water only when dry, and a few drier weeks in winter (Iowa State Extension, Ohio Tropics). One grower had a cutting flower within a year in a greenhouse (Vermont Hoyas, kerrii); on a windowsill, count in years and let it surprise you.

Two things never to do. The flowers grow from short woody spurs, and the same spur flowers again every year. When the flowers fall, leave the spur alone; cutting it off is cutting off future flowers (Iowa State Extension, The Houseplant Guru). And once buds appear, do not move or turn the plant until the flowers are over; sudden changes make it drop its buds (Iowa State Extension, NParks).

When something looks wrong

Look at the soil first, and then at how much light it gets. Almost everything else follows from those two.

• A single heart that never grows. A leaf with no node. It can live for years as it is and will not become a vine. Enjoy it, or slide it out and look for a piece of stem at the base; if you want a plant that grows, buy one that is already vining (Iowa State Extension, Ohio Tropics).
• Soft, thin, wrinkled or puckered hearts. Check the mix. Dry and light: soak it through, and the hearts firm up over a few days. Wet: the roots are damaged; let it dry fully and slide it out to look (NC State Extension, Iowa State Extension). Watering in sips does the same as not watering.
• Yellow leaves. Usually the soil: wet too long, or bone dry too long, which yellows the lowest leaves first. Also a pot too large, too little light, or a great deal of direct sun, which turns every leaf a lighter yellow-green (Iowa State Extension, Ohio Tropics). Read the mix, then the light.
• Leaves dropping. Rot on wet mix, or weeks bone dry, or cold on a winter windowsill, or a sudden move. Check the mix and roots, keep it above 13 C and off cold glass, and keep its spot steady.
• No new growth for months. Often nothing is wrong: this is a slow plant, slower still in winter and in the variegated form, and a cutting roots before it leafs (RHS profile, Ohio Tropics). More light and warmth, 21 C or above, are the two things that speed it up (Ohio Tropics). An old compacted mix slows it (Iowa State Extension).
• No flowers. Youth, light, water, warmth, pot size, cut spurs, in that order. Bright window, snug pot, water only when dry, every spur left on, a drier winter, and time (NC State Extension, Iowa State Extension).
• Cream margins fading, new leaves greener. Too little light reduces variegation; brighter light brings the markings back on new leaves (Clemson HGIC, Ohio Tropics).
• Scorched patches, burnt vine tips. Direct sun on a plant not used to it, or very dry air (Clemson HGIC, Ohio Tropics). Filter the light, introduce sun over a few weeks, raise the humidity in winter.
• Black or brown spots. Leaves left wet without airflow, or a fungal spot; brown scabby lesions on old leaves are harmless (Iowa State Extension, Clemson HGIC). Water the mix not the leaves, remove the worst, treat early if it spreads.
• Mealybugs. White cottony tufts in the leaf joints and under the hearts. Dab each with a cotton bud in rubbing alcohol, spray the whole plant with insecticidal soap or horticultural oil, repeat weekly for a few weeks, and check the undersides (Clemson HGIC, Ohio Tropics).
• Scale. Small hard brown bumps with sticky residue (Iowa State Extension). Wipe or scrape them off, wipe with insecticidal soap or oil, repeat.
• Spider mites. Pale speckling and fine webbing in dry warm air, often by winter heating (Clemson HGIC). Shower the plant, undersides included, every few days, spray with neem or insecticidal soap weekly, raise the humidity.
• Black mushy base, wilting on wet mix. Root rot. Cut away every dark soft root, repot in fresh dry mix in a snug pot, water only when fully dry, and take cuttings of healthy stem with a node straight away in case the plant does not recover (Clemson HGIC, Vermont Hoyas, propagation).
• Long bare vines. Normal. A hoya sends a runner out with long gaps and leafs it later. Wind it onto a support, give more light, and do not cut it back (NC State Extension, Pistils Nursery).

Propagation

By stem cuttings with a node, in spring or summer. A leaf on its own will often root and then sit there for years; it needs a piece of stem, with at least one or two nodes, to grow into a plant (Iowa State Extension, NC State Extension). Wear gloves for the sap. Take a piece of mature but not woody vine with two or more nodes and a couple of leaves, and either stand it in water or push it into moist perlite up to the first leaves, warm and humid in bright indirect light; roots come within weeks, usually four to six (Iowa State Extension, Vermont Hoyas, propagation). Pot the rooted cutting into the chunky mix in a small pot and give it the same light and the same dry spells as its parent. Then be patient: a kerrii cutting roots first, and even with a node it can take a very long time to grow on (Ohio Tropics); growers report many months to a year or more before the first new hearts. The RHS also layers it in spring or summer: pin a length of stem to a pot of mix beside the plant and cut it free once rooted (RHS profile).