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A hoya is any plant in the genus Hoya, which Kew's Plants of the World Online places in the family Apocynaceae, native from tropical and subtropical Asia to the western Pacific. The common houseplant is Hoya carnosa, the wax plant; a UF/IFAS production guide says wax plants in the foliage plant trade are primarily its cultivars. NC State Extension recommends bright indirect light and a fast-draining mix that dries between waterings, and says most plants do not flower until they are 2 or 3 years old.
What is a hoya?
POWO currently lists 566 accepted Hoya species. NC State's genus page describes them as "epiphytic, climbing, evergreen herbaceous perennials," says the name "commemorates Thomas Hoy, the 18th-century gardener to the Duke of Northumberland," and says wax plants are "so named for their thick, waxy leaves."
Hoya carnosa (L.f.) R.Br. is native to "S. China to Laos, Japan (S. Kyushu) to Taiwan," per POWO, which describes it as "a climbing epiphyte or lithophyte." NC State notes that the epithet means "fleshy," for the thick, succulent leaves, and lists honey plant and porcelain flower as other common names. POWO, the RHS and Missouri Botanical Garden place it in Apocynaceae; NC State's H. carnosa page and the ASPCA list Asclepiadaceae. NC State lists the growth rate as rapid, while the UF/IFAS Master Gardener plant ID page calls it "a slow-growing, evergreen vine."
Common types of hoya
Some types are cultivars of H. carnosa; others are separate species.
| Type | How to recognize it | Native range |
|---|---|---|
| H. carnosa 'Krimson Queen' (also 'Tricolor') | Leaves "have a green center, encircled with creamy white to pink margins" (NC State) | Cultivar of H. carnosa |
| H. carnosa 'Krimson Princess' | Has "green leaves with pink and white variegation, dark green margins" (NC State) | Cultivar of H. carnosa |
| H. carnosa 'Compacta' (also 'Krinkle Kurl', Hindu rope) | Leaves "are folded over and gives them a rope-like appearance" (NC State) | Cultivar of H. carnosa |
| H. kerrii (sweetheart hoya) | Has "thick, heart-shaped green leaves" and small pink flowers with red centers (NC State) | "Indo-China to W. Malesia" (POWO) |
| H. linearis | Described as "trailing, slender stems, fleshy linear leaves," with fragrant white flowers; NC State adds "hard to grow" (NC State) | "Nepal to China (NW. Yunnan) and Indo-China" (POWO) |
| H. curtisii | Small, spade-shaped, waxy, dark green leaves "with greenish-silvery variegations," 1 to 2 inches long (NC State) | "Thailand to Peninsula Malaysia, Borneo, Philippines" (POWO) |
| H. pubicalyx | Has "long, narrow, glossy dark green leaves that transition to silvery-pink in sunlight" and pink flowers (NC State) | "Philippines (Luzon)" (POWO) |
| H. australis | Leaves "thick, smooth, green, and round or elliptical," fragrant white flowers with red centers (NC State) | "N. Borneo, Sulawesi, New Guinea to SW. Pacific" (POWO) |
POWO lists Hoya compacta C.M.Burton as a synonym of H. carnosa, and NC State says the 'Compacta' cultivar is "sometimes called Hindu Rope plant." H. kerrii is often sold as a single rooted leaf, but NC State says those cuttings "are not likely to grow well unless a bit of the stem tissue was included with the leaf when it was cut."
The care advice below is guidance for H. carnosa, the species. For the genus as a whole, NC State says most species "need bright light, dappled shade, or full morning sun" and "a free-draining, organic potting mix that dries out between watering."
How much light does a hoya need?
"Bright indirect light year-round is ideal," says NC State, which lists partial shade, with 2 to 6 hours of direct sun. MBG asks for "bright light with at least 1/2 day of direct sun" but calls the plant "tolerant of curtain-filtered sun and bright indirect light." Clemson Extension puts wax plant in its high-light group (500 to 1,000 foot-candles preferred) and notes it "may also be conditioned to grow in medium light." The light meter calculator converts a phone reading to foot-candles.
How often to water a hoya
NC State says "Allow the soil to dry out between watering," warns that "Too wet or too dry soil can cause the leaves to drop," and says to use room-temperature water because "Cold water can shock this plant." UF/IFAS Gardening Solutions says to water from spring through fall once "the top third or half of the soil" has dried out completely, and "In the winter, water very sparingly." MBG warns that "Overwatering may cause root rot."
Potting mix and repotting
NC State recommends "a loose, fast-draining potting mix high in organic matter and a container with good drainage." It says to repot when the plant outgrows its container and "is not in bud or flower," into a pot no more than 2 inches larger, and adds: "It doesn't mind being pot-bound." NC State's genus page warns that a container that does not keep the plant root-bound "may hold excess water, which can lead to root rot." See the repotting guide.
Humidity and temperature
NC State says "This plant loves high humidity" and suggests a humidifier or a tray of wet pebbles; see do humidity trays work before relying on a tray. The plant can spend summer outdoors in partial shade, but NC State says to "Bring it back inside when nighttime temperatures fall below 50 degrees F."
Climbing or trailing
MBG says the stems "will climb counterclockwise around wire or other thin trellis-like structures" and "will also trail from hanging baskets." See also climbing indoor plants, trailing indoor plants and the moss pole guide.
How to get a hoya to flower
- Give it time. "Most plants will not produce flowers until they are 2 or 3 years old," per NC State.
- Give it light. UF/IFAS Gardening Solutions says a lack of light "is usually the main reason that hoyas don't flower," and MBG says "Good light is necessary for flower production."
- Leave the spurs. NC State advises against pruning the peduncle ("spur") where flowers formed, "as this will repeatedly produce flowers over several years. Cutting off these stems is cutting off future flowers." MBG agrees: "new flowers will form on the old spur."
- Don't move it once buds form. "Pots should not be rotated or moved to another location after flower buds appear," says MBG.
- Know the species. NC State notes that "Some species are shy to flower," and for H. kerrii that "Overwatering can also inhibit the plant's ability to flower" (NC State).
What hoya flowers are like
NC State describes H. carnosa flowers as "white to pink and hairy, with five-point centers, in clusters of up to 30," fragrant, and blooming in spring, summer or fall, and notes "They may produce a sticky sap." MBG gives each flower up to 1/2 inch across with "a distinctive, star-shaped, red-centered corona," and the RHS calls them "night-scented." H. kerrii flowers "produce copious amounts of reddish-brown nectar, which drips from the flowers and can stain fabrics, walls and furnishings" (NC State).
Pruning and propagation
"If pruning is necessary, it is best done in early spring before its rapid growth begins," says NC State; leave the flower spurs. UF/IFAS Gardening Solutions says to "take care not to let the sap from cut stems drip onto furniture."
NC State says to "Propagate the wax plant by stem cutting." The UF/IFAS production guide describes single-node cuttings set "so the node is at the soil surface to ensure maximum rooting," and says that in commercial production, "Cuttings root in 3 to 4 weeks." For H. kerrii, include some stem with the leaf, as noted above.
Common hoya problems
| Problem | What the source says | More help |
|---|---|---|
| Decline in wet soil | "Overwatering may cause root rot" (MBG) | Root rot |
| White, cottony insects or scale | Mealybugs "can be a problem" (NC State); MBG says to "Watch for mealy bugs and scale" (MBG) | Mealybugs, scale |
| Small flies over the pot | Fungus gnats "are attracted to potting mixes that are too wet" (NC State) | Fungus gnats |
| Spider mites | They "can appear when the air is too dry" (NC State) | Spider mites |
Are hoyas toxic to cats and dogs?
These ASPCA Toxic and Non-Toxic Plants entries name a hoya. Each gives a non-toxic verdict and lists no clinical signs:
| ASPCA entry | Other names on the entry | Scientific name as listed | Listed as |
|---|---|---|---|
| Honey Plant | Wax Plant | Hoya carnosa | Non-toxic to dogs, cats and horses |
| Wax Plant | Hindu Rope Plant, Porcelain Flower | Hoya carnosa 'krinkle kurl' | Non-toxic to dogs and cats |
| Hindu Rope Plant | None listed | Hoya carnosa 'krinkle kurl' | Non-toxic to dogs and cats |
| Porcelain Flower | Hindu Rope Plant | Hoya carnosa 'krinkle kurl' | Non-toxic to dogs and cats |
| Sweetheart Hoya | wax hearts, valentine hoya | Hoya kerrii | Non-toxic to dogs, cats and horses |
| Silver Pink Vine | None listed | Hoya publcalyx (spelled this way on the entry) | Non-toxic to dogs, cats and horses |
These entries cover H. carnosa (including 'Krinkle Kurl'), H. kerrii and H. pubicalyx; none of them names H. linearis, H. curtisii or H. australis. Check the scientific name: the ASPCA's Variegated Wax Plant entry is Echeveria sp., not a hoya.
Non-toxic does not mean harmless to eat. The ASPCA's plant list notes that "the consumption of any plant material may cause vomiting and gastrointestinal upset for dogs and cats." If your pet ate part of a hoya and seems unwell, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435; the ASPCA says a consultation fee may apply. See also cat-safe plants.
Frequently asked
Sources: Kew POWO: Hoya, Kew POWO: Hoya carnosa, Kew POWO: Hoya kerrii, Kew POWO: Hoya linearis, Kew POWO: Hoya curtisii, Kew POWO: Hoya pubicalyx, Kew POWO: Hoya australis, NC State Extension: Hoya carnosa, NC State Extension: Hoya, NC State Extension: Hoya kerrii, NC State Extension: Hoya curtisii, NC State Extension: Hoya australis, Missouri Botanical Garden: Hoya carnosa, RHS: Hoya carnosa, UF/IFAS Gardening Solutions: Hoya, UF/IFAS Master Gardener: Wax Plant, UF/IFAS: Wax Plant (Hoya) Production Guide, Clemson Extension: Indoor Plants: Light Requirements, ASPCA: Honey Plant, ASPCA: Wax Plant, ASPCA: Hindu Rope Plant, ASPCA: Porcelain Flower, ASPCA: Sweetheart Hoya, ASPCA: Silver Pink Vine, ASPCA: Variegated Wax Plant, ASPCA: Toxic and Non-Toxic Plants, ASPCA Animal Poison Control Center