Hoya carnosa

Identification

Hoya carnosa is a hairless climber (apart from its flower clusters) whose robust, pale gray, smooth stems can reach 6 m ^[1]. RHS describes it as a vigorous, stem-rooting climber to about 5 m ^[3]. Grown indoors it usually stays much smaller; Missouri Botanical Garden gives 2–4 ft for house plants ^[6].

The leaves are the main field mark. Flora of China describes the blade as broadly ovate-cordate to ovate-oblong or elliptic, 3.5–13 cm long and 3–5 cm wide, with a rounded to shallowly cordate base, a blunt or shortly pointed tip, and about four pairs of lateral veins that are hard to see ^[1]. The petiole is 1–1.5 cm long ^[1]. NC State describes the leaves as thick, leathery and waxy, sometimes flecked with silver or cream-white ^[5].

The flowers come in globose, finely hairy clusters on a peduncle about 4 cm long, each flower on a 2–4 cm pedicel ^[1]. The corolla is white, sometimes pink in the center, 1.5–2 cm across, with triangular lobes that are densely papillate inside and bent back at the tips ^[1]. The corona lobes spread in a star on top of the corolla ^[1]. RHS and Missouri Botanical Garden both describe the center as red ^{[3, 6]}. The seed pods are narrow follicles 6–10 cm long ^[1].

Flora of China splits the species into two varieties. The typical var. carnosa has plain deep green leaves, while var. gushanica has leaves spotted on the upper side ^[1].

Look-alikes. Hoya pubicalyx has longer, oblong to oblong-obovate leaves (10–14 cm) with a distinctly pointed tip ^[8]. Hoya australis in New South Wales has leaves densely hairy underneath ^[9]. Hoya lacunosa has much smaller flowers, 0.6–0.7 cm wide ^[2].

Naming and trade labels

The accepted name is Hoya carnosa (L.f.) R.Br. ^[10]. NC State lists Hoya compacta and Hoya intermedia as names the plant was formerly known by ^[5], and WCVP also treats both as synonyms ^[10]. WCVP also sinks var. gushanica into the species, although Flora of China keeps it as a separate variety ^{[10, 1]}.

Most plants sold today are cultivars. NC State lists ‘Compacta’ (also sold as ‘Krinkle Kurl’ and called Hindu rope plant, with folded, rope-like foliage), ‘Krimson Princess’, ‘Krimson Queen’ (which it equates with ‘Tricolor’) and ‘Variegata’ ^[5]. RHS lists ‘Tricolor’ as having white-splashed leaves ^[4]. See the separate pages for H. carnosa ‘Compacta’, ‘Krimson Queen’ and ‘Krimson Princess’.

Growing it

Unlike most hoyas, this species has care guidance written specifically for it by RHS, Missouri Botanical Garden and NC State.

• Light. All three institutions ask for bright light, but they differ on direct sun. Missouri Botanical Garden suggests at least half a day of direct sun and says the plant tolerates filtered or bright indirect light ^[6]. NC State recommends bright indirect light ^[5], and RHS warns that hot summer sun can scorch hoya leaves ^[4]. Once buds appear, do not move or turn the pot ^[6]. See the light guide.
• Water. Water moderately but regularly in the growing season, letting the mix become nearly dry between waterings ^[6]. NC State notes that both overly wet and overly dry soil can make leaves drop ^[5]. See the watering guide.
• Potting mix and pot size. Use a loose, fast-draining mix high in organic matter. The plant tolerates being pot-bound, and NC State advises a new pot no more than 2 inches larger than the old one ^[5]. RHS recommends peat-free, loam-based compost for glasshouse plants ^[3]. See the substrate guide and repotting guide.
• Temperature. RHS gives a minimum night temperature of 10°C in winter ^[4]. MoBot likewise says wintering plants tolerate night temperatures down to 50°F ^[6]. The RHS plant profile gives it hardiness rating H2, a survival rating for plants that tolerate low temperatures but not frost ^[3]. Treat 10°C as the practical floor.
• Pests. RHS, NC State and Missouri Botanical Garden all name mealybugs. NC State adds fungus gnats in over-wet mixes and spider mites in dry air, and MoBot adds scale ^{[3, 5, 6]}. See hoya pests and root rot.

Flowering

NC State says most plants do not flower until they are 2 or 3 years old. Bloom can come in spring, summer or autumn ^[5]. Each cluster may carry 10–30 flowers according to Missouri Botanical Garden ^[6], or about 30 according to Flora of China ^[1]. RHS describes the scent as strongest at night ^[3]. NC State notes the flowers may drip a sticky sap ^[5].

Leave the flower stalks (peduncles) on the plant, because new flowers form on the same spurs year after year ^{[6, 5]}. RHS lists insufficient light as a likely cause when a hoya fails to flower ^[4]. For more detail, see why a hoya is not blooming and hoya peduncles.