Name: porcelain flower, wax plant or hoya (Hoya carnosa).
Plant type: twining vine needing support.
Foliage: thick mid-green leaves.
Climate: temperate to tropical; best grown indoors in cool to cold areas.
Soil: a free draining mix, such as the mix used for cymbidium and bromeliads.
Position: indoors—good light but not direct sun through glass; outdoors—some shade from hot sun in summer.
Flowering: dense half globes of small, pink, wax-like flowers with red centres; other colours are available.
Feeding: apply a six-month controlled-release fertiliser at the start of spring; don’t feed over winter.
Watering: keep moist but never wet; good drainage is essential; reduce watering over cooler months.
Hoya originated in southern India, and has been grown as indoor or outdoor potted plants for several hundred years. All parts of the plant have a waxy look and feel, but the stems do become woody on older plants.
The leaves are mid-green and quite thick with a lighter central vein. New growth appears as long, deep red tendrils, which should be twined around a sturdy plant trainer secured in the pot or against a wall or adjacent timber lattice.
The flower heads are circular and densely packed with waxy flowers, each on its own slender stem. They produce an abundance of clear, sticky nectar that is very attractive to bees. They are also delicately perfumed.
Wax plants flower in spring and summer. When the flowers fade and fall, they leave behind a spur or stub on the end of a short stem. Do not cut the stem or the spur, because the next flowers will be produced from its tip. Over many years, the spurs themselves can grow to 3 or 4cm in length.
There are many varieties of the common wax plant, with flowers ranging in colour from almost white to deep pinkish red. There are also other species of hoya, but they are quite rare and can be difficult to source from plant retailers.
Hoya is often grown as an indoor plant, but in tropical areas where temperatures are warm to hot all year, it can also be grown in the garden and trained up nearby trees. In all other climatic regions it is best grown in pots in protected positions, either outside or, in cooler areas, indoors or in a heated glasshouse.
Unlike most other plants, hoya likes being pot-bound! It does not like having its roots disturbed by repotting every two or three years and will display its displeasure by not flowering.
When growing hoya, choose a pot that is just slightly larger than the existing root ball. Take the plant from its old pot and, without removing any soil or mix from its roots, transfer it to the new pot and backfill with premium-quality African violet mix or terracotta and tub mix. Make sure it is an open mix that will drain well.
Young plants can be twined up a small plant trainer inserted firmly into the pot. Larger plants may do better if they are trained up a trellis or mesh that is attached to a nearby pergola, tree trunk or fence.
Another tip when growing hoya is to limit its sunlight. Outdoor plants should be positioned so they are partially shaded from hot afternoon sun in summer, which can burn its leaves.
Indoors, hoya should be placed where it will receive good ambient light but not direct sun through glass, which will burn leaves. A light curtain is often enough to protect from sun scorch.
Don’t put your plant close to air-conditioning or heating vents, and never put it in the bathroom!
When the weather is warm, hoya should be kept moist, but never wet. Remember, it doesn’t have a lot of potting mix around its roots, and what it does have will dry out quickly on a hot day, so do give it a drink each morning over summer.
As the weather cools, gradually reduce watering frequency so by mid-winter in sub-tropical to temperate areas you are watering only once every two or three weeks. Test the mix regularly—if the top few centimetres are dry, give it some water.
While wax plants like a bit of humidity, don’t leave the pot standing in a saucer of water. If the inside air is very dry, spray a light mist over the plant every day or so, or place a bowl of water alongside your wax plant.
The best hoya fertiliser is a bi-month controlled-release fertiliser for flowering plants. Apply this at the start of spring each year and supplement every month or so with a liquid or water-soluble plant food to keep plants healthy and vigorous.
Aphids are the most troublesome pest of wax plants— they are attracted by the abundant nectar when flowers are present. Sometime ants may also drink the nectar.
Common pests can be controlled with sprays of insecticidal soap or pyrethrum.
Growing hoya from cuttings
Peace lily: hardy indoor plant that produces white spathes.
African violet: indoor flowering plant with dark green, velvety leaves, and flowers from white to deep purple-red.
Phalaenopsis: moth orchid enjoying similar indoor conditions to hoya.
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