Hooray for the Hoyas!
by Mary Francis, Fairfax Master Gardener Intern
Hoya flowers
Hoyas, also known as waxplants or porcelain flowers, are popular and easy to grow houseplants. They are native to Asian countries, particularly India, the Philippines, Vietnam, Bangladesh, Indonesia and Polynesia; there are also many species native to Australia. Hoyas are frequently found as epiphytes in nature. They were among the plants collected by the Scottish botanist Robert Brown during an expedition to Australia aboard the Investigator, which set sail in 1801 upon the urging of Sir Joseph Banks. Robert Brown named the genus after Thomas Hoy, who was the long term gardener of the Duke of Northumberland. Hoy was the first to popularize Hoyas as house plants in England.
The genus Hoya belongs to the Asclepias (milkweed) family and includes at least 500 species. They are twining vines with typically thick, fleshy and waxy leaves. There is considerable variation in the appearance of plants within the genus. In different species the leaves vary in size from smaller than a quarter to about 4 inches across; leaves may be flat or curled, rounded or more lanceolate in shape. Leaf color may be simply deep green or combinations of green, white, cream or pink. Some species have pink stems. Since hoyas are vines they are ideally suited for planting in hanging baskets, or in a pot with a trellis. Smaller species are suitable for a shelf with no support.
Mature Hoyas are prized for their flowers. Flowers appear in spring and are dainty with a citrus scent. Depending on species, flower colors range from white to deep pink to yellow. Failure to flower is usually due to immaturity, insufficient light or no fertilization.
How to Grow Hoyas
Hoyas prefer a well-drained soil. Amending organic potting soil with either peat, coco chips or orchid mix is a good option. Hoyas tolerate or even prefer to be partly rootbound so repotting should be delayed until the plant has clearly outgrown its pot. Choose a new pot one size bigger than the old pot.
The light requirements of Hoyas vary by species; most prefer bright to medium indoor light and a few tolerate low light. Some species may summer outside in morning sun so long as they are carefully acclimated to the increased sunlight. Others need much more shade. Hoyas are tender plants that cannot tolerate cold temperatures below about 50 degrees F.
Fertilize them lightly with balanced fertilizer no more than once a month. Hoyas don’t really require fertilization if one is satisfied with only foliage. A mature plant is unlikely to flower if not fertilized. Some growers cease fertilization altogether during the winter.
The soil of Hoyas should be kept moist but not wet. One may allow the soil to dry out somewhat before watering. Overwatering can be fatal by inducing root rot. Hoyas love high humidity. Rocks in the saucers of the plant will raise the humidity around the plants. Be sure the plant itself does not contact the wet stones. Some growers drastically reduce watering in late winter to (hopefully) stimulate spring flowering.
Hoya carnosa
These plants can be easily propagated via cuttings so long as the cutting has at least one node. Single leaves are not suitable for propagation. The leaf may root, but no plant will develop. Cuttings may be placed in water to root. Alternatively, cuttings can be placed in seed starting soil after dusting the cut end with rooting hormone. Cuttings done in soil will need added humidity that can be provided by putting them in a plastic bag until they root.
If you are fortunate enough to have a flowering Hoya, after flowering do not damage the base of the flowers. These parts (peduncles) are used to produce the next round of flowers and are best left alone.
Overall Hoyas are remarkably disease free and grow happily even if their ideal conditions are not met. They are sometimes victims of mealy bugs or spider mites. They may develop root rot if the soil is too heavy or wet. They need to be untangled once in a while.
Among the hundreds of species of Hoyas, the most well-known is Hoya carnosa with its dark-green shiny leaves of good substance. This plant has been popular for years and may be one that you remember from your grandmother’s house. Hoya carnosa ‘variagata’ is very similar. It has leaves with an irregular white margination. The two plants are almost identical in other regards as to appearance and habit. They enjoy lasting popularity because they are beautiful, long lived and easy to grow.
Hindu rope plant, 3 years old
Another worthy plant is Hoya carnosa ‘Compacta’, also called the Hindu rope plant. Its leaves are small and curled and may be dark green or variegated. It grows slowly, and as its tendrils lengthen they also curl giving a particularly attractive effect. Hoya curtisii is a slow growing miniature species. Hoya kerri has beautiful, rather large heart shaped leaves.
Many wonderful Hoyas are available in reputable retail stores or through the internet. With so many species, it is actually possible to fill your home with Hoyas, all of them different, interesting and beautiful.
Resources
Hoya carnosa, North Carolina State Extension Plant Toolbox
Hoya, University of Florida Gardening Solutions
Hoya carnosa, Colorado State Extension Plant Talk
Hoyas as Houseplants, Penn State Extension, November 2020