Hoya (Hoya spp.) is called wax plant because its fleshy leaves and clusters of star-shaped flowers look as if they were cast from that glossy substance. An occasionally shrubby but mostly vining genus native to tropical Asia, New Guinea, and Australia, hoya climbs or cascades to 20 feet or more. Its leaves range in length, according to species, from 1/2 to 10 inches and its night-fragrant flowers in diameter from 1/2 to 3 inches. Hoya's hardiness varies from U.S. Department of Agriculture plant hardiness zones 9 to 11, but it is most often grown as an easy-care houseplant.
In a Good Light
Due to its rain forest origins, hoya doesn't tolerate much direct sun, but does require very bright light to bloom. To provide the ideal environment for your plant, place it on an east-facing windowsill where it will receive sunlight for about three hours in the early morning and bright, indirect light for the rest of the day. It will also flourish under grow lights timed to run for 12 to 16 hours per day. During the summer months, you can hang the plant beneath a tree or porch roof where the sun's rays only reach it during the early morning or late afternoon.
High and Dry
In its native environment hoya often grows on trees, so it prefers a fast-draining potting soil, such as a cactus mix. Water that soil thoroughly, but wait until the top one-third to one-half of it dries before you water the plant again. Add 1/2 teaspoon of a high-phosphorous plant food such as 12-55-6 to every gallon of water you use during the spring and summer. Don't feed the plant in fall and winter unless it is under grow lights during that time.
Keep your plant slightly potbound, as it is more likely to bloom if its roots are a bit crowded. Hoyas usually flower during the spring or summer, although some types can bloom intermittently all year given the proper conditions. Don't move your plant after it has begun to set buds, or it may drop them. Refrain from pinching or snipping off the spent flowers, as the short and leafless stems on which they appear – also called spurs or peduncles – will produce more flowers in subsequent years if they aren't broken off.
Your hoya may suffer from insects such as aphids, mealybugs, or scale, which respectively resemble green lice, bits of fluff, or brown bumps. To deal with them, spray the plant thoroughly with a dilute solution of insecticidal soap – 1 tablespoon per gallon of water – every three days for 15 days. Don't spray when the temperature is above 80 degrees Fahrenheit or you may damage the plant.