Hoya aka Hoya Rangsan

Growth rate is generally rated medium, though NC State's profile for Hoya carnosa specifically calls it rapid once established. As a trained houseplant, Hoya carnosa typically reaches about 2–4 feet (0.6–1.2 m) in height with a 1–2 foot (0.3–0.6 m) spread, but as an unpruned climbing vine it can grow considerably larger over time — RHS notes some species "can grow quite large" and benefit from annual pruning to keep them in check.

Hoyas are frost-tender and prefer average room temperatures of about 16–24°C (61–75°F) during spring and summer. They tolerate cooler conditions but not freezing, with a recommended minimum night temperature around 10°C (50°F) for Hoya carnosa (a bit higher, around 16°C, for more tender species like H. lanceolata ssp. bella). In winter they become semi-dormant and prefer to be kept cooler and drier; always water with room-temperature water, since cold water can shock the plant.

Hoya flowers are strongly and often heavily fragrant, with the scent typically most noticeable in the evening or at night — RHS specifically describes the fragrance as strongest after dark, and Wikipedia notes a nocturnal, almost pheromonal quality to Hoya carnosa's scent.

Hoya flowers are borne in rounded umbel clusters of small, waxy, star- or crown-shaped blooms with five fleshy petals, in colors including white, cream, pink, and deep red/burgundy, often with a contrasting center. Plants usually don't flower until they are two to three years old and need bright light to bloom reliably. Once a flowering spur (peduncle) has bloomed it will continue producing flowers for years, so it should never be pruned off, and plants shouldn't be relocated once flower buds have formed, as sudden light changes can cause bud drop.

Hoya is a large genus, with commonly cited species counts ranging from roughly 300 to over 550 depending on the taxonomic treatment (500+ is the most frequently quoted figure). Popular cultivated species and cultivars include Hoya carnosa (and cultivars like 'Tricolor', 'Rubra', 'Compacta'), H. lanceolata ssp. bella, H. pubicalyx, H. kerrii, H. lacunosa, H. multiflora, H. retusa, and H. wayetii, spanning trailing, climbing, and more compact growth habits with variously colored and patterned foliage.

Hoyas are frost intolerant and, outside of warm climates, must be grown as houseplants or in a greenhouse/conservatory. Missouri Botanical Garden lists Hoya carnosa as winter hardy only to USDA zones 10–12; in the UK, RHS describes hoyas as tender and recommends growing them indoors year-round or moving them outside only in summer (after hardening off) and bringing them back in before night temperatures drop too low. NC State similarly notes plants can spend summer outdoors on a shaded patio but should come back inside once nights fall below about 50°F (10°C).

Hoyas generally need only light pruning, best done in late winter or early spring before new growth begins, and they don't respond well to hard pruning. Crucially, avoid cutting the flowering spurs (peduncles) after bloom, since the same spur reflowers for years — removing it removes future flowers. Left unpruned, some species can get quite large, so annual light pruning can help keep plants a manageable size.

Hoyas tolerate being pot-bound and can stay in the same container for several years. Repot in spring, only once the plant has outgrown its pot and isn't currently budding or flowering, moving up to a pot only a little larger than the current one — NC State recommends no more than about 2 inches larger, and RHS similarly advises a pot just a few centimetres bigger than the rootball.

Hoyas are easy to propagate, most commonly from stem cuttings; air layering and layering or semi-ripe cuttings taken in spring/early summer are also used.

Yellowing is most often linked to overly wet, poorly-drained potting mix — hoyas are intolerant of soggy soil and wet roots, and prolonged excess moisture can lead to root rot, a common underlying cause of leaf yellowing. Make sure the pot drains well and let the mix dry appropriately between waterings.

Brown, crispy patches or leaf tips typically point to moisture stress from too little water or overly dry air, while soft, mushy brown patches suggest overwatering and root rot. Dry air can also invite spider mites, which cause stippled, browned foliage.

Drooping is usually tied to watering issues: hoyas can be shocked by cold water, so always water at room temperature, and both prolonged over- and under-watering (soggy or bone-dry mix) can cause wilting.

Leaf drop is commonly tied to inconsistent soil moisture — NC State notes that soil that is either too wet or too dry can cause hoya leaves to drop. RHS similarly cautions against letting growing conditions swing too abruptly, noting flower buds can also be shed if light levels change suddenly.

Overall growth rate is rated medium by NC State's genus profile (though rapid once established for Hoya carnosa specifically). The most common cause of slower-than-expected growth or reluctance to flower is insufficient light — most hoyas need bright, indirect light (or partial sun) to grow and bloom well, and RHS notes failure to flower is often traced to too little light.

Common pests across sources include mealybugs, spider mites (favored by dry air), aphids, scale insects, glasshouse whitefly, and fungus gnats (drawn to overly wet potting mix). The main disease concern is root rot, caused by excess moisture or poor drainage in a container that holds too much water.

Various cultures have historically used hoyas medicinally, a practice that has contributed to population declines of some species in parts of their native range. No further pharmacological or clinical detail was found in the sources researched.

Hoya carnosa was shown in research at the University of Georgia to be an effective remover of indoor air pollutants. Beyond this, hoyas are primarily valued for ornamental use — as hanging basket or specimen houseplants prized for their waxy foliage and fragrant flowers.