Hooked on Hoyas

By William Scheick, Contributing Editor

An ongoing online debate about hoyas hooked my attention several years ago.

Left with questions, I contacted two hoya growers to help me sort out fact from fiction about these still-popular, old-fashioned plants.

Hoyas include exquisite trailing or climbing plants featuring shooting-star clusters of fragrant flowers. They are easy to fall for and impulsively adopt. Then, before you know it, you might find yourself thinking of them as children — because, like children, these plants can be challenging to care for.

At least that’s the impression given at garden forums, where concerned hoya parents chronicle ongoing problems with their beloved little ones. Often, the advice they routinely receive consists of so many prohibitions that anyone not familiar with hoyas might imagine these tropicals should be called “don’t-do plants.”

Hoya variables

Are these long-lived, indoor/outdoor beauties really so finicky? Their fussiness is overrated, Christine Burton told me.

Before she died last year at the age of 90, she had raised hoyas since 1943. A passionate and outspoken advocate for correct species identification, Christine founded the first hoya society in 1978 and also for many years co-managed a related web-discussion group.

She edited The Hoyan, which included 57 issues between 2002 and 2014. Even so, she did not want me to consider her a hoya expert. “I would like to become the authority I’ve been accused of being before I die,” she told me, “but there is still so much to be learned that I doubt I or anyone else can ever become a true hoya authority in one lifetime.”

She was not being humble or coy. There are more than 250 hoya species, and their individual requirements vary. A few are succulents, while most are not.

Plant care comparable to childcare

Anyone who grows many different hoyas should be prepared for responsibilities akin to childcare.

Even Christine, who over the years had grown every available hoya, preferred to maintain a pared-down collection of about 50 different species and six cultivars. “Just having the name hoya doesn’t mean it is a desirable plant,” she explained. “Once I’ve studied an undesirable species, I get rid of it.”

Such tough-love emerges only among advanced hoya enthusiasts.

H. Carnosa is a robust climber and a good choice for beginners

For beginners, Christine recommended easy-to-grow, nonvariegated H. carnosa (wax plant) and H. australis subspecies tenuipes (porcelain flower).

H. Australis is a good choice for beginner Hoya growers

It’s tempting to get hooked on hoyas, but go slow, she cautioned. “Don’t buy all 100 names you see on a sale list, and don’t buy anything simply because it’s new or because you saw a picture of its flowers and fell in love with it.”

Do this, not that

Loving hoyas only goes so far. There is upkeep, such as the often-repeated “do-not-repot” rule. This rule overstates the fact that hoyas perform best with somewhat crowded roots. Eventually they do need to be repotted — “the fast growers every year and others only every three or four years,” according to Christine.

When repotting, she advised, “don’t use the largest planter you can find, but select a pot only a size larger than the present one.” Flowering, which may be slow at first, increases as hoyas become established in their new containers.

“Do not repot,” it seems, has mushroomed into “do not disturb.” That’s just a silly rumor, Christine insisted, adding that “do not disturb” doesn’t apply even to hoyas on the verge of flowering.

“The only danger in moving a budding hoya is that, if one isn’t careful, a flowering branch can be broken," she said.

Sometimes, in fact, careful disturbance proves to be helpful, such as slowly rotating a hoya to enhance its exposure to light and thereby ensuring more evenly distributed foliage.

“Do not prune” has also been exaggerated and should more accurately be revised as “prune with caution.” For hoyas that grow to be top-heavy or unattractive, Christine recommended substantial trimming, including the flower stalks (peduncles).

Some hoyas bear gorgeous shooting-star floral clusters (umbels) on new peduncles. Other hoyas flower for years on the same peduncles. With these latter types, such as H. carnosa and H. australis, it is important not to snip off any nectar-producing organs located in the sepals (calyxes) on the flower stalks.

Hoya flowers strike some people as peculiar looking. To Susan March, they could seem “rather comical as they hang upside down from their stems.” A cutting from H. carnosa at her home eventually became an office plant in the School of Nursing at University of Texas Arlington, where Susan (now retired) was once a longtime marketing coordinator and webmaster.

The first time her oldest hoya bloomed, she thought her mother had placed a plastic flower on her plant as a joke.

She was hardly alone in that reaction. Each spring her office plant became a conversation piece because, on first sight, visitors did not believe the fragrant flowers could possibly be real.

Considering that her “provocative” office plant was more than 30-years old, Susan appreciated that it and her hoyas at home had somehow withstood what she confessed as her “neglectful nature.”

She admitted, however, that hoyas do present some challenges. One year she had to cut her oldest one down to the roots because of an out-of-control insect infestation. More generally, however, “the hardest part of raising them is to avoid overwatering, and to find the ideal spot for them, and then to just leave them alone.”

Atrophied hoya stems signal insufficient water, while brown-spotted foliage indicates too much moisture. Rainwater fosters hoya health by supplying beneficial acidity, but water free from chemical treatment can also be used.

Sometimes Susan’s office hoya became “a little messy.” Then pruning, including peduncles, seemed in order.

“Hoyas are best pruned by removing entire branches, right at or very near soil level,” Christine advised. While blooming will be interrupted, the pruned plant will quickly recover and produce new flower stalks. But keep in mind, Christine emphasized, that hoyas can’t be kept compact and should also be expected to flower profusely.

Hoya health care

While flowering requires ample light, an often-repeated rule insists that hoyas should not receive direct sunlight.

This rule goes too far.

While most hoyas evolved in understory habitats beneath tree canopies, no single directive about sunlight suits all of them. Hoya foliage can desiccate easily during an ill-timed or prolonged exposure to our Texas sunlight, especially during summer.

On the other hand, direct early-morning sunlight (7 –10 a.m.) often works wonders when followed by plenty of bright but indirect light.

Rigid yellow leaves can result from too much light, while dark green leaves and no blooms tend to indicate too little light or too much nitrogen. H. carnosa, Christine has found, tolerates shady settings well and can bloom profusely on a screened-in porch facing north.

Established hoyas benefit from a high-potassium fertilizer (ideally 5-50-17), at 1/4 the amount recommended on the label, applied when watering regularly and thoroughly during warm seasons. The plants require less moisture during winter, when Christine switched to a 0-10-10 fertilizer.

Hoyas prosper in humid conditions. Before Christine purchased a mist-o-matic, she had hosed the floor of her greenhouse every day and let natural evaporation bathe her plants. She also hand-misted them and relied on fans to provide beneficial air circulation.

Humid, hot and high

Most hoyas thrive in high-temperature environments, including greenhouses at 120. F, as long as these settings remain humid. Obviously, then, these tropicals, especially when budding, respond poorly to blasts of cold air (including air-conditioning vents).

Even so, as Susan’s office plant proves, hoyas are not the shrinking violets they are often made out to be. Contrary to common perception, hoyas will survive temperatures below 60. F. “Sixty degrees is the ideal low,” Christine reported, “but over 15 years none of the hoyas in my greenhouse suffered when night temperatures dropped to 40 degrees.”

Asked for one more insider tip — perhaps a particularly personal one — Christine shared a private ritual with her hoyas. “I talk to my plants,” she told me. “While I’m talking I look at them, and that’s when I notice little things I otherwise might miss, such as a mealy bug to be swabbed away with an alcohol-dampened Q-tip. Talking to them saves my plants by stopping an infestation before it starts.” Good advice, and not only when child-caring hoyas.

Wax or honey plant (H. carnosa), a robust climber from India, is a commonly available hoya and a good choice for beginners. Another easy-to-grow choice for beginners, this common twining subspecies of porcelain flower (H. australis sub. tenuipes) climbs vigorously.

Christine Burton named Hoya kentiana for the late Hon. Douglas H. Kent, Fellow at Kew and British Museum, who was her hoya mentor.

Hoya curtisii, native to the Malayan Peninsula and Philippines, frequently shows up in overflowing eight-inch pots at big-box stores.

H. Compacta Regalis may be more trouble than it's worth

Hoya compacta ‘Regalis’ sometimes shows up in big-box stores, but Christine Burton recommended ignoring this “maternity ward for mealy bugs,” which hide in this plant’s folded leaves. She preferred to rename the plant “Hoya troublliana.”

H. Pubicalyx produces red flowers

One of Christine Burton’s favorites, cultivar Hoya pubicalyx ‘Pink Silver’ produces wine-red flowers and also a sap looking like maple syrup rather than the milky latex more common among hoyas.

H. Nummularioides

If Christine Burton had been limited to only one hoya, she would have chosen H. nummularioides. This heavenly-scented, sprawling shrub from the jungles of Thailand produces flowers that stand out beautifully against dark-green foliage.

H. Lanceolata

Haling from India and also known as beautiful hoya, this gorgeous and sweet-smelling miniature wax plant (Hoya lanceolata ssp. bella) fascinated nineteenth-century European plant collectors. It was featured as plate 236 in volume 5 (1849) of the Belgian horticultural journal Annales de la Société royale d’agriculture et de botanique de Gand: Journal d’horticulture.

Final tips from Burton

• Hoyas are best pruned by removing entire branches, right at or very near soil level. Take care when cutting and unwinding the branch. I find the task is best done in steps, starting at either end.
• Cut out the vine, two nodes at a time, leaving about an inch below the lower node. Before cutting, put a clip-type clothespin on the part of the vine you leave behind to help you find that same branch again. Otherwise, if you let go of the vine or look the other way, it is very easy to lose track of it.
• Keep taking two-node cuttings until the entire branch is removed. By cutting the branch in two-node stages, the vine is easily untwined without damage to the cuttings or to the branches that are left. This type of pruning creates space for air to circulate among the remaining branches and your plant is not left with a lot of ugly dried up stubs that detract from its beauty.