How to Care for a Hoya (Wax Plant)

Light

Light controls whether a hoya flowers. Iowa State Extension recommends bright, indirect light, often from the brightest window in the house. It should be bright enough to read by and to cast a shadow, but not direct sun on the leaves. Strong direct sun can scorch the leaves or turn them red. Too little light gives long, thin stems with few leaves and no flowers. UF/IFAS agrees that a lack of light is usually the reason a hoya won’t bloom.

Watering

In the wild, hoya grows on tree branches, where its roots dry quickly between rains. Copy that with a wet-dry cycle. Water thoroughly, so the whole root ball is moist and water runs out the drainage holes. Then let the mix dry substantially before watering again. Sources differ on how dry. UF/IFAS says to let the top third to half of the soil dry out completely. Iowa State says to let the mix dry almost completely.

Push a finger into the mix or lift the pot to judge it. A dry pot is noticeably lighter. In bright, warm months you’ll water more often. In winter, when growth slows, UF/IFAS says to water very sparingly. NC State adds that cold water can shock the plant, so use room-temperature water. Water the soil rather than the leaves. Iowa State links leaf spots to foliage that stays wet without good air movement.

Overwatering is what kills hoyas. Iowa State calls overwatering in a poorly draining mix the quickest path to root decline. Underwatering is less common. It shows as wrinkled or soft leaves that firm up after a good drink. NC State notes that soil kept either too wet or too dry can make leaves drop.

Potting mix, pot and drainage

Use a chunky, airy mix that drains fast but holds some moisture. Iowa State suggests potting soil combined with orchid bark and perlite or pumice. The pot needs drainage holes. Keep it small: hoyas bloom best slightly pot-bound, and a large pot holds water around the roots for too long. A hanging basket shows off the trailing vines. A trellis, hoop or moss pole encourages fuller growth and more places for flowers to form.

Temperature and humidity

Iowa State puts the best indoor range at 65 to 80°F and says hoya does not tolerate temperatures below 55°F, so keep it away from cold windows in winter. Slightly cooler nights than days help buds form.

Average indoor humidity is fine. Iowa State considers 40 to 60 percent ideal. NC State says the plant enjoys high humidity from a pebble tray or humidifier, which helps in a dry, heated house.

Feeding

Feed lightly and regularly in spring and summer. Iowa State recommends an all-purpose fertilizer at one-quarter to one-half strength, skipping every second or third watering, or a slow-release fertilizer at the label rate. Don’t feed in winter. The rest helps the plant flower the following season.

Flowering and the spur rule

The clusters of waxy, star-shaped flowers form on short stalks called peduncles, or spurs. The same spur blooms again and again for years. When flowers fade, let them drop on their own and leave the spur alone. Cutting spurs off removes future flowers.

Be patient with young plants. NC State says most hoyas don’t flower until they are 2 or 3 years old. Blooms can appear in spring, summer or fall. Once buds form, keep care steady. Iowa State warns that moving the plant, changing the watering pattern or a temperature swing can make buds drop.

Repotting

Repot only when the plant has clearly outgrown its pot, or when the mix has broken down and no longer drains. Don’t repot while it is in bud or bloom. Move up just one size, no more than 2 inches wider than the old pot, and use fresh, airy mix.

Pruning

Hoya rarely needs pruning. If you do need to shorten long vines, NC State suggests early spring, before fast growth starts. Avoid the flower spurs. The cut stems leak a milky sap, a trait of its family, the dogbane family that includes milkweed and oleander. UF/IFAS warns not to let sap from cut stems drip onto furniture.

Propagation

Stem cuttings are the reliable method. Take a piece with one or two nodes and strip the lowest leaves. Set the node in water, moist sphagnum or a light propagation mix, in warmth and bright indirect light. Roots usually form within a few weeks. Then pot the cutting into a small container of well-draining mix.

A leaf without a node will root but never grow a vine. Iowa State notes this is why the single heart-shaped Hoya kerrii leaves sold around Valentine’s Day often stay unchanged for years.

Pests and problems

• Healthy growth, no flowers: too little light, too big a pot, too little summer feeding, a young plant or spurs cut off. Fix the light first.
• Buds drop: a sudden change in watering, temperature or location. Keep conditions steady.
• Yellow leaves, wet soil: overwatering or a mix that drains poorly. Lengthen the dry period and repot into a chunkier mix.
• Stalled growth: low light, cool rooms or old, compacted mix.
• White cotton in leaf joints: mealybugs, the most common pest. Treat with horticultural soap or a labeled insecticide.
• Immobile bumps and sticky residue: scale.
• Stippled leaves, fine webbing: spider mites, usually in very dry air.
• Small flies around the pot: fungus gnats, drawn to mix kept too wet.

Inspect new plants closely before setting them next to others. Catching pests early makes them much easier to control.

Pets and children

The ASPCA lists wax plant as non-toxic to dogs and cats, and NC State also lists it as non-toxic to horses.

Outdoors

A hoya can spend summer outside on a partly shaded patio, out of direct sun. NC State says to bring it back in when nights fall below 50°F. In frost-free areas such as south Florida, UF/IFAS says it can grow outdoors year-round where temperatures stay above 45°F, in a spot shaded from harsh direct sun, which burns the leaves. A hanging basket under a porch roof or a tree canopy works well.