The perennial hibiscus is a tremendously popular plant that's equally effective in group plantings or as a specimen planting. Although it won't flower year-round like the tropical hibiscus found in USDA zones 9-10, this hardy bloomer with its plate-sized flowers will lend a distinctively tropical air to northern and southern summer gardens alike. Does this Spark an idea?
Location
The perennial hibiscus commonly found in garden centers is Hibiscus moschuetos. A South Carolina native, they're able to tolerate summer heat as far south as USDA zone 10 in sub-tropical Florida, yet will survive the winter cold of a zone 4 climate.
Growing Conditions
Although quite tolerant of poor soil, perennial hibiscus will thrive if planted in well-drained soil rich in organic matter. They will do quite well growing in light shade, although a full sun location will encourage stronger growth and more prolific flowering. It's also wise to grow them in a somewhat sheltered area since high winds can wreak havoc with the tall, thin stems of a mature plant.
When to Plant
Plant perennial hibiscus in early spring to allow the plant time to get established before the summer blooming season begins. Flowering is most prolific in mid to late summer, but many cultivars will bloom into fall, often up until the first frost. Be wary of transplanting them too late in the season. Doing this won't allow the plant sufficient time to adapt to its surroundings and become established before the first frost, and thus will likely be more susceptible to damage from the cold weather conditions.
Plant
When you've picked the spot to plant your hibiscus, amend the soil in the area by adding compost and dried manure and working it into the soil. This will help your plant's blooming capabilities throughout the growing season. Then, dig a hole about twice as wide as the root ball of the plant, and after removing it from its pot, sit the plant in the hole so that the top of the root ball is about level with the ground. You can then fill the planting hole with the amended soil, and water well.
Hibiscus are fast growers and can reach a height of 6-8-feet with a spread of 3-4 feet within two years, so if you're planning to plant several of these plants, make sure you space the planting holes to give the plants adequate room to grow.
Care
Once established, the perennial hibiscus is quite drought tolerant, but for optimum growth and flowering, you may want to water at least once a week, especially if the weekly rainfall amount is less than an inch. Hibiscus will respond more favorably to an infrequent drenching than they will to a lighter, more frequent watering, but as with any new transplant, new hibiscus plantings will need more frequent waterings until they become established. Mulching will help preserve moisture, but make sure that the mulch is kept at least two inches away from the plant stem so as to avoid southern stem blight.
The compost you added to the planting hole will help your plant thrive, but you may want to augment this with a sprinkling of a time-release fertilizer specially formulated for flower growth. After the flowering season ends and the first frosts threaten, the foliage will die back. This is the time to cut back all stalks to the ground. The following spring, the hibiscus will send up new stalks and begin its rapid growth in readiness for its stunning summer display.
Pests
Aphids and whiteflies can sometimes be a threat to hibiscus, but these can usually be controlled with an occasional application of a mild solution of water and regular dish soap dispensed from an spray bottle. Other pests include the Japanese beetle and the hibiscus sawfly, both of which can be controlled with an application of an insecticide such as Orthene.
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