Hoyas are popular houseplants with long trailing stems, waxy leaves and fragrant flowers. Some varieties of hoyas bloom in spring and summer, some flower in fall and winter, and some bloom sporadically throughout the year. Although there are between 300 and 400 varieties, the wax plant (Hoya carnosa) is most commonly grown.
Hoyas are slow growing with long woody stems. All hoyas have thick fleshy leaves with a waxy coating, but the color, shape and size vary depending on the variety. Clusters of creamy white to pink star-shaped flowers hang from the plant; some people find the fragrance of the blooms disagreeable. Hoyas contain milky sap that can stain clothes, furniture or walls.
Grow hoyas outside in U.S. Department of Agriculture plant hardiness zones 10b and 11 in light shade. In colder zones, grow hoyas inside in a window with bright light. Hoyas do not tolerate direct sun or temperatures below 45 degrees Fahrenheit. During the growing season water thoroughly, allowing the top third of the soil in the container to completely dry out. Water sparingly in the winter. Mist plants with a spray bottle to maintain 40 percent to 60 percent humidity.
Some hoyas bloom during their first year, while others do not flower until they are larger or more mature. New flowers grow from the bases of old flowers, which are called bloom spurs. Pruning the spurs off will reduce or delay flowering. If a hoya is not blooming, try moving it to an area with more light and apply a fertilizer with more phosphorus (the middle number on the label). Hoyas bloom better when they are root bound. If the flowers turn brown and mushy, or yellow and spongy, the soil is too wet. If the blooms dry up and fall off the plant, the soil has dried out too much between waterings. Cool drafts cause the flowers to drop off soon after they open.
Mealy bugs, small cottony insects, infest the stems and the undersides of the leaves on hoyas. Spray plants with a horticultural soap mixture to control mealy bugs. Nematodes can be a problem when hoyas are grown in the ground outside. Grow hoyas in containers to avoid damage from nematodes. Root rot is caused by soil that is too wet and soggy. Use a potting mixture that drains freely and do not overwater.