Few plants bring a more tropical ambiance to the garden than Hibiscus. Their large, showy flowers are evocative of Hawaiian beaches and sunshine. It is almost hard to believe that many of these stunning plants are winter hardy in our harsh Wisconsin climate.
There are essentially three distinct types of Hibiscus that we carry here at the Gardens.
Hardy / Dinner Plate Hibiscus
Hardy Shrub Hibiscus
Hardy/Dinner Plate Hibiscus (Hibiscus moscheutos)
This plant will have passersby rubbernecking as they pass your garden! Customers are frequently disbelieving when assured that these lush perennials, bearing dramatic flowers up to 12” across, are indeed winter hardy in Wisconsin. Hardy Hibiscus produces thick, sturdy, upright woody stems up to 1” in diameter. Height will vary from 36” -60”, depending on the variety. Leaves are maple-like and some varieties have burgundy or copper colored foliage. The “wow” factor, though, comes from the immense dinner-plate sized flowers. These show-stopping flowers are borne in profusion in late summer/early autumn. Flower color includes white, shades of pink & raspberry and even fire-engine red.
Dinner Plate Hibiscus appreciate ample moisture and perform best in full sun. They are reliably hardy in our area but are very late to emerge in spring, frequently not breaking dormancy until June. Be patient! I often wonder how many Hardy Hibiscus are dug up and disposed of before they have the chance to begin growing in the spring. The previous year’s woody stems should be cut down to 4”-6” in spring (you may need a pair of loppers for this task!). In early summer the stems can be pinched back (before July 4th) to improve branching and yield more flowers. Once spent, the enormous flowers are best removed in order to keep the plant looking tidy.
Rose-of-Sharon (Hibiscus syriacus)
This large, upright, multi-stemmed shrub is valued for its bloom time as well as its range of flower color. Late summer tends to be a time of very little color in the shrub border and this plant fills that niche, offering showy single or double flowers for many weeks. The flower colors include white and shades of pink and rose as well as truly striking lavender-blue.
Rose-of-Sharon prefers full sun and appreciates protection from winter winds. Mature height will be 6’-10’, depending on variety, and width can reach 5’-8’. Flowers are formed on current season’s wood so pruning, if desired, should be done in late fall or winter after leaves drop or in early spring before buds form.
Tropical Hibiscus (Hibiscus rosa-sinensis)
Tropical Hibiscus is a tender plant with shiny green leaves and large, showy flowers in a truly astounding range of colors. In Wisconsin this plant is grown as a seasonal patio plant that will bloom all summer long. Tropical Hibiscus must be brought indoors before frost in the autumn if the gardener wishes to overwinter it. Cut the plant back to within 6” of the main stem, provide it with as much light as possible and monitor for insects during the winter months. Tropical Hibiscus will frequently drop many of its leaves during its winter indoors. It should recover once spring arrives.