Growing Outrageously Colorful Tropical Hibiscus (Hibiscus rosa-sinensis)
By Laurelynn Martin and Byron Martin
These large, eye-catching, dinner-plate sized hibiscus represent the words “tropical flower” better than any other. Originating in Asia and the Pacific Islands, Hibiscus is the national flower of Malaysia and the state flower of Hawaii. Decades of intense cross breeding with the rosa sinensis species has produced some unbelievable multi-colored blooms. The American Hibiscus Society was formed in 1950 to promote, develop and improve upon the hundreds of varieties that were quickly emerging.
Single vs. Double
There is both single and double flowering tropical hibiscus in the rosa sinensis species. The ‘Fancy’ cultivars have growth habits of both upright and spreading. Within this group, reside two general forms: the brightly colored, usually sold colored single blooms (sometimes double) that propagate easily and are often used as seasonal potted plants as well as tropical landscape shrubs. hese are often sheared to hedges in frost-free landscapes.
The second form has much larger blooms, which have a diverse mixture of colors and patterning usually single but sometimes double and are often delightfully eye-catching in their beauty. These plants make excellent container plants where they often can be enjoyed on a deck or patio or grown inside year-round in the northern climates. Their abundant array of colors are exciting to watch as many will turn different colors as the blooms age.
The multi-colored blooming hibiscus plants are often slower in growth when compared to their landscape counterparts and a bit more difficult to propagate. At Logee’s, we focus on the multi-colored flowering varieties because of their outrageous beauty.
The cultural requirements are the same for both types of hibiscus. They require full sun for optimum growth but they will grow and flower under partial sun that is half a day or more of direct sunlight. Of course, flower production does suffer some. For best results, a southern exposure with full sun will produce the most flowers over a season. As the days shorten, during winter in the north, often times plants will stop bud formation as the light intensity is not strong enough. Flower buds can fall off as the plant as it doesn’t have the energy to continue their development.
Hibiscus need warm temperatures: Above 60°F or higher is preferable, although they can take dips into the 40’s or high 30’s. Do not grow under continuous cool temperatures because they will suffer and even die.
At Logee’s, we grow hibiscus with a wet to almost dry cycle when watering them. Simply allow the soil to become visually dry between waterings (but avoid a severe wilt) and then thoroughly saturate the potting mix. If this is done on a constant basis, the plants will thrive and the root systems will remain healthy.
As hibiscus plants are relatively fast growers, they need regular applications of fertilizers throughout the growing season. A balanced fertilizer, either in a liquid form which is added to the water or a granular organic that is top dressed on the soil, will do the trick. Formulations like a 7-9-5 with trace minerals or an organic 6-4-6 will produce the most flowers and growth. Also, a pearled, slow release fertilizer works well to release nutrients continuously over a couple of months. Remember during the active growing season, spring to fall, hibiscus need consistent fertilization for the highest flower production.
Most peat based potting mixes that are available work well for growing hibiscus. They are slightly acidic and generally have a starter fertilizer included in their mixture. The standard potting mix is a combination of peat, perlite, and vermiculite.
Hibiscus plants are susceptible to various insects. Whitefly, spider mites and aphids are the most common, along with thrip under certain conditions. It’s important to monitor the plants closely, especially when they come inside from their outdoor summer growth. A spray with neem oil can eradicate most problems but it’s best to do preventative sprayings before their move inside.
Pruning needs to be done to encourage a bushy form and maintain height and size. This can be done from early spring to early fall, although pruning will slow down flowering as the buds form on the growing tips. We find that a late winter/early spring pruning will give time for the new growth to form flower buds.
Some cultivars leaves turn yellow caused by environmental stress or edema. The mature leaves up and down the stem turn yellow and the leaves fall off. This condition will not harm the plant; it will just look sparse for a bit. Pay attention to the humidity, soil moisture and day and night time temperature differentials. Usually leaf yellowing happens during the change of seasons but once the season shifts, new healthy leaves will appear.