Hoya (Wax Plant): Growing Guide

Hoya, also known as the wax plant, is a genus of evergreen tropical plants belonging to the Asclepiadaceae subfamily. The genus includes approximately 250–300 species, some of which are cultivated as house and greenhouse plants. In the wild, hoya can be found in South China, Australia, and India, growing along rocky slopes and on tree trunks in forests.

The plant was named by the renowned botanist Robert Brown, who is also known for the theory of Brownian motion. He described hoya in 1810 and named it after his friend Thomas Hoy, a gardener for the Duke of Northumberland. Hoy worked for many years in the Duke’s greenhouse and was passionate about cultivating tropical plants.

Plant Description

Hoya is a climbing vine, with natural stems reaching up to 10 meters in length. Indoor varieties are smaller, typically growing to about 5–6 meters. Young hoya stems have a purple-brown hue, and leaves develop over time. In addition to leaf blades, mature stems produce aerial roots. As the plant matures, its stems turn green and eventually become woody.

Hoya leaves grow in opposite pairs and have a leathery, waxy texture with grayish speckles. This unique appearance has earned it the common name “wax plant.” The size and color of the leaves vary by species. New leaves tend to be glossy but become matte with age. Some species have hairy foliage. The leaf shape can range from oval to egg-shaped or heart-shaped.

During the blooming season, hoya produces fleshy, umbrella-like clusters of flowers in the leaf axils. Each cluster can contain up to 50 small, five-petaled flowers. Flower shapes differ by species, with individual blooms typically measuring 1–2 cm in diameter, though the imperial hoya has flowers up to 6 cm wide. The center of the corolla features a raised “crown” formed from fused floral structures, often in a contrasting color. The petals appear velvety and come in soft shades of white, pink, green, and brown. After one flower fades (lasting from a few days to three weeks), another forms in its place. The overall blooming period lasts from May to October.

Hoya flowers are highly fragrant and produce abundant nectar, making them attractive to pollinators. The peak nectar production occurs in the evening and nighttime, which is when the plant’s scent becomes most intense. Different species have distinct floral fragrances.

General Care Guidelines

Hoya is an undemanding plant that does not require high humidity, frequent watering, or nutrient-rich soil. It also does not need frequent repotting.

Temperature

  • During active growth, hoya thrives at temperatures between 17–25°C (63–77°F).
  • In winter, it can tolerate as low as 10°C (50°F), though a minimum of 15°C (59°F) is preferable.
  • Hoya bella (the beautiful hoya) is more sensitive to cold and may lose its leaves if winter temperatures drop too low.

Lighting and Placement

  • Hoya prefers bright light but does not tolerate direct summer sunlight.
  • It grows well in a south-facing room, where it can climb walls as a trailing or hanging plant.
  • Avoid moving the plant frequently, as relocating it may cause it to drop buds and even leaves.
  • Hoya is ideal for summer balcony decor as it enjoys stable environments.

Humidity

  • Humidity is not a crucial factor for hoya, but it thrives in slightly humid environments.
  • During summer, occasional misting is beneficial.

Watering

  • Water moderately, allowing the soil to dry out between waterings.
  • In winter, water sparingly. Hoya can withstand short periods of drought.

Fertilization

  • Apply fertilizer twice a month during the growing season (starting in March).
  • Do not fertilize in winter.

Blooming

  • Hoya blooms only with adequate lighting.
  • Proper winter care is essential for flowering success. The plant should be kept in a bright, cool room (10–15°C or 50–59°F) with minimal watering.
  • To stimulate blooming, soak the pot in warm water for 2 hours and mist the plant with water at 30–40°C (86–104°F).
  • Avoid moving the plant after buds appear, as this may cause them to drop.
  • Do not cut off flower stalks after blooming, as new flower clusters will grow from them the following year.

Soil

  • Hoya is not picky about soil. In nature, it grows on rocky surfaces and tree trunks.
  • It can thrive in nearly any soil mix. A recommended mix includes equal parts leaf mold, turf soil, humus, peat, and sand.
  • Alternatively, use a mixture of clay-turf soil, leaf mold, and greenhouse soil (2:1:1 ratio).
  • Ensure good drainage at the bottom of the pot to prevent root rot.

Repotting

  • Repot hoya infrequently, about once every 2–3 years or less.
  • To encourage abundant flowering, use a tight-fitting pot.
  • For vigorous vine growth, opt for a larger container.
  • Ensure the pot has drainage holes and proper drainage material.

Propagation

Hoya can be propagated by seeds, cuttings, or layering, but cuttings are the most common method.

  • Each cutting should have at least two pairs of leaves.
  • Cut between the nodes and root cuttings in water or a mix of peat and sand.
  • Roots typically develop within 3–4 weeks at temperatures above 20°C (68°F).

Layering Propagation:

  • This method allows hoya to bloom in its first year.
  • Make a small cut on an old vine, wrap it in moist sphagnum moss, and cover it with plastic wrap.
  • Once roots appear, cut and transplant the rooted section into a pot.
  • Alternatively, lay a portion of the stem on soil in a new pot, secure it, and cover it with moist moss. Once rooted, separate it from the parent plant.

Propagation Tip:

  • Use only mature, already flowering plants for propagation.

Crown Formation

To encourage branching, the plant should be pinched after the fourth leaf appears. Overly long shoots should be trimmed, which promotes more intense blooming. The stems require support; threads are often used to secure the plant to a window or wall.

A wire ring can also be used by simply placing its ends into the pot. The pot should be heavy enough to prevent the plant from tipping over.

Diseases, Pests, and Possible Issues

Most common Hoya species are resistant to pests and diseases. However, under poor care conditions (excessive heat or overly dry air), they may be affected by scale insects and red spider mites. In this case, the plant should be treated with an insectoacaricide.

Hoyas can also suffer from root nematodes. The soil for repotting must be steamed to eliminate any potential infestation.

  • Leaf drop – This may result from overwatering or simply relocating the plant to a different window. Leaf loss can also occur due to cold soil conditions in winter, such as when the plant is placed on a cold windowsill or watered with cold water during hot weather.
  • Leaf spots – May indicate either insufficient light or sunburn.
  • Failure to bloom – Usually due to inadequate lighting or overly warm winter conditions. A warm shower may help stimulate blooming.
  • Pale, curled, or dry leaves – Too much direct sunlight; the plant should be slightly shaded.
  • Dropping flower buds and flowers – This can be caused by relocating the plant or exposure to excessively hot and dry air.
  • Slow growth and pale green leaves – A sign of nutrient deficiency in the soil. Repotting may be necessary.