Hoya Carnosa “Tricolor” is one of numerous cultivars of the Hoya genus of woody climbing plants that are prized for their foliage and for their clusters of waxy, star-shaped flowers. Hoyas are native to tropical Asia and will grow outdoors in U.S. Department of Agriculture plant hardiness zones 10b and 11. In cooler growing zones, Hoyas are grown indoors in hanging baskets. If growing conditions are not ideal, “Tricolor” may not yield its soft pink flowers for years or perhaps never, although once it does begin flowering, it should do so dependably for years. Its conditions for flowering are the same as other Hoya cultivars.
To promote flowering, the International Hoya Society (IHS) recommends keeping Hoyas in extremely bright, indirect light but not directly in the sun. If you put your plant in a south-facing window, it may yield more flowers but the leaves may turn rigid and yellow. In poor light, it will yield dark-green leaves but no flowers. Try placing a Hoya in a window that faces east or west. A horticulturalist at North Dakota State University (NDSU) recommends four hours of direct sunlight each day. Recommendations of how much sun an indoor Hoya should receive are never accurate for all locations because the sunlight intensity changes based on latitude and seasons. If your climate is warm enough to grow a "Tricolor" outdoors, place it in light shade.
IHS recommends that you fertilize your "Tricolor" with a weak solution of a balanced fertilizer. A balanced fertilizer contains equal amounts by weight of nitrogen, phosphorous and potassium. If your plant is not flowering, IHS says to give it a jolt of fertilizer that is high in phosphorous, while a horticulturalist at NDSU recommends a fertilizer high in potassium. IHS says that while both phosphorous and potassium will encourage plants to produce flowers, most fertilizers touted as encouraging blooming have a higher amount of phosphorous.
Hoyas evolved in humid climates and flower best in humid conditions. Although it is difficult to maintain high humidity in a home, you can encourage Hoyas to flower by misting them with a spray bottle if necessary to maintain a 40 percent to 60 percent humidity in the area where they are growing.
Often it's easier to grow Hoyas indoors by giving them 12 to 14 hours of artificial light a day. Getting them to bloom may require about 18 hours of artificial light a day with six hours of rest. The NDSU horticulturalist advises that if your plant is not blooming with natural light, give it supplemental artificial light with a wide-spectrum fluorescent lamp.
- University of Minnesota Extension: Growing Wax Plant – Hoya Carnosa
- University of Florida Extension: Hoya Carnosa Wax Plant, Wax Flower
- North Dakota State University Extension: Questions on Hoya
- University of Saskatchewan Saskatchewan: The Hoya: Long-Lived and Trouble Free
- International Hoya Association: Frequently Asked Questions