The hibiscus is a member of the mallow family which encompasses nearly 300 species including trees, shrubs, perennials and annuals. Although native to the warmer tropical regions, there are a few species known to our southern states.
In our northern climate, Hibiscus rosa-sinensis is the species most commonly available through nurseries, garden centers and florists. These are bred specifically for flower size and color and make great house plants as well as being wonderful additions to a summer garden. Hibiscus rosa-sinensis is not winter hardy, and therefore must be brought in before the first fall frost.
The beautiful, exotic-looking flowers are short-lived, typically blooming for only one day. Once finished blooming, a self grooming feature begins; the flower will close up and drop off. There is also a shell-like structure supporting the flower. This too withers and drops a few days after the flower fades.
Hibiscus are generally easy plants to grow and should pose few problems if cultural requirements are followed.
- Soil: A rich, well-drained soil mixture is desirable. A good potting mix could contain two parts potting soil, two parts peat moss and one part perlite or vermiculite.
- Temperature: Being a tropical plant, the hibiscus does not tolerate cold temperatures. Warm temperatures are needed for flower buds to develop. Indoors, they should be grown in a warm, sunny location where daytime temperatures are no lower than 55°F; 65° to 75°F is best for optimum growth. Otherwise, if it is too cold, flower buds may drop off or fail to form altogether. Hibiscus cannot withstand extreme fluctuations of temperatures or humidity. Therefore, avoid placing them in drafty areas, near radiators, on TVs, or in entryways where they'll be blasted with cold air from time to time.
- Light: Hibiscus require very bright light to bloom well indoors. A sunny western or southern exposure that has at least 4-5 hours of bright, direct light is best. The more light they have, the better they'll bloom, indoors or out.
- Water: The soil should be kept relatively moist, not saturated. Never allow the soil to dry out to the point of wilting. Check the pot to make sure drainage holes are present. Water from the top of the soil down so that water runs out the bottom holes. This leaches soluble salts from the soil which would otherwise accumulate. It also ensures that the bottom roots are watered thoroughly. Excess water should be drained off. During the winter months, allow the soil to dry out a bit more between waterings.
- Fertilizer: Hibiscus are heavy feeders and require a balanced fertilizer such as a 20-20-20 or 10-10-10. Use at half the label recommended strength every 2-3 weeks when placed outside for the summer. Indoors, fertilize less often, using ½-strength formulation, every month or so in spring and summer; less frequently in winter.
- Pruning: Pruning should take place in late winter to encourage a bushier plant. Any leggy growth that may have shot up can be selectively trimmed back to the rest of the plant. Hibiscus can withstand a fairly heavy pruning, so don't be afraid to give your plant a good haircut, especially if you want to maintain a smaller plant. Just remember you'll be pruning off flower buds in addition to the foliage, so it will take longer to bloom.
- Propagation The easiest method of propagating these plants is from vegetative cuttings. This involves taking 3"-5" cuttings from the strongest shoots available. Dip the cut ends in a rooting hormone compound, tap off the excess and stick in a small pot filled with a light potting mixture. Keep slightly moist and place in a well lighted area. After 3-5 weeks, they should develop a good root system and be ready for transplanting. In order to encourage a bushier plant once the cutting has rooted, cut or pinch off the top inch of stem to just above a leaf node, where a leaf joins the stem.
These plants benefit tremendously from being placed outdoors after danger of frost. However, before placing them directly in full sun, it is important to acclimate them to the brighter conditions. Begin by first moving the hibiscus to a porch, then to filtered light under a shade tree and finally into the bright sunlight.
Reverse the process in the fall so that the plant is indoors before the first frost. By easing the plant into the different conditions, one can prevent bud loss and minimize foliage loss.
Yellow leaves: Abrupt changes in soil moisture, air temperature or drafts. Avoid excessive watering especially with older varieties. Some yellowing is normal in spring or fall when growing conditions are in transition. Yellowing may signal need for fertilizer.
Bud drop: Too cold or too hot. Needs (daytime) 65°F-75°F to develop buds. Avoid drafts. Too little or too much water. Low light conditions.
Pests: Most common insects are aphids and spider mites. Keep foliage clean by washing periodically. Use insecticidal soap or insecticides labeled for use on hibiscus if necessary.