Sally Ayotte and Gladys Fowler
It's hard to beat the tropical hibiscus for flamboyancy. With their bold colours, large blooms, and glossy deep green leaves they bring to mind the tropics of south Florida or Hawaii or perhaps Singapore. The tropical hibiscus, Hibiscus rosa-sinensis belongs to the mallow family and is related to okra, cotton, and hollyhock to name a few. There are thousands of colours and varieties with blossoms ranging from 2 inches in diameter to 10-12 in. Some varieties grow only a foot in several years while others will easily climb 15 feet if left unpruned.
You can successfully grow tropical hibiscus in pots and enjoy these beautiful plants year round. Hibiscus can be grown in fairly small containers relative to their size. Both the pot and soil mix must allow for fast drainage since waterlogged roots are fatal to hibiscus. One part compost to one part commercial potting mix (made up of peat moss, perlite, and vermiculite) works well. Fill the container to about inch below the rim and add a thin layer of mulch on the top. Mulch can be made of bark, pine needles, wood shavings, cedar mulch. Mulch acts as insulation from temperature changes, protects surface roots from damage, conserves moisture and it breaks down adding extra nutritional matter.
Hibiscus in containers can be fully exposed or sunk into the ground as long as the soil is well drained. In summer, hibiscus do better in morning sun and afternoon shade. Introduce your plant to outside conditions slowly in late May starting with an hour or two a day gradually increasing the amount of time outdoors over ten days. Once established outside add diluted liquid fertilizer high in potassium and micronutrients every two weeks for large plants. Now you can sit back and enjoy those tropical blooms outdoors.
In mid to late September move your potted hibiscus indoors first checking for bugs. As a precaution mix one and a half teaspoons of dishwashing liquid (with no phosphates) and a pinch of baking soda in one liter of water and spray on the undersides of leaves rather than the surface. Repeat this again after several days before bringing the pot indoors as aphids and spider mites can be a problem when hibiscus are grown indoors. Plants can be lightly pruned in the fall when bringing them indoors however new plants may need no pruning for the first year. Be prepared for some buds and leaves to turn yellow and drop after the plant has been brought indoors.
Light is crucial for hibiscus in the winter months. It's important to provide the best light possible, a window or patio door on the south side of the house is ideal. The larger the window the better. Hibiscus like humidity and you can increase the humidity around your plant by: grouping it with other plants, by filling saucers under the container with watered pebbles, and by misting your plant. Hibiscus like to dry out between watering.
Hibiscus require much less water in winter than in times of active growth. Do not feed hibiscus with fertilizer unless they are actively growing so generally from the end of Nov. until early March they do not need to be fed. In February a growth spurt is triggered as the days get longer. This is the time to prune your plant. Prune stems on an angle cutting away one quarter to one third of each stem just above a node. This will ensure that blooming will begin by late spring or early summer bringing you the beauty of the tropics once again.
In comparison with tropical or indoor hibiscus there are perennial hibiscus that are hardy in our area. Hibiscus syriacus, better known as The Rose of Sharon , Hibiscus moscheutos or Rose Mallow.
The Rose of Sharon is well adapted to dry climates and prolonged drought. It is often used as the backbone shrub in flower borders and in the right climate it makes an effective hedge. This plant is more multi branching and vase shaped than the tropical hibiscus. The flowers are cup shaped and remind you of hollyhocks (a cousin). Some syriacus blossoms are like bells and some are double. Even though their flowers are smaller than the giant blooms of other hibiscus hybrids, they make up for it in their wonderful soft colours of pinks, lilac, purple, pure white, blue, mauve, and maroon.
The Rose of Sharon prefers full sun, good drainage, and water during the growing season. It also likes a protected site and winter mulching since it can be a bit tender in our area. It does not like to have root competition from other plants. This plant benefits from pruning. Prune only in the winter and cut them back by removing about half the bush. If it is not pruned it will become unattractive and the flowers will be smaller. Pruning ensures health.
Hibiscus moscheutos is a hardy herbaceous shrub, meaning it dies down each winter and comes up again in spring. This shrub can grow 3-6 feet and its flowers can be 12 inches across. These mammoth blooms come in rich colours of red, crimson, pink just to name some of the colours. These shrubs do take more care. They may need to be staked because their flowers are so heavy and the plant itself is so tall that wind causes them damage. They require more water than other hibiscus. Feed them over the summer and watch for insects. These plants are vulnerable to disease.
Do not prune this plant. Let it die down in the fall and then do a tidy up around it. The remaining stems can be trimmed to a few inches above the ground and mulch. In the spring you just clear the mulch away and let the plant grow. Be patient because they come out late in the spring. These hybrids are not for windy climates.
Try bringing your tropical Hibiscus outdoors and planting perennial Hibiscus species - it is well worth the effort for the ooos and aaahs you’ll get from visitors to your garden. Happy gardening!