Richard Bogren, Gill, Daniel J.
For Release On Or After 07/04/09
By Dan Gill
LSU AgCenter Horticulturist
For the summer season, no flowering tree or shrub outblooms the crape myrtle. This small tree packs a powerful punch of color over an amazingly long season. But other summer-blooming large shrubs and small trees can do a lot to contribute to the summer display. Here are a few –
Vitex or chaste tree
In gardening, flowers that are called blue often have a slight lavender tint or may be bluish-purple (true-blue flowers are few and far between). Such is the case with vitex (Vitex agnus-castus). For about a month, this deciduous large shrub or small tree produces showy 5- to 7-inch spikes of small lavender-blue flowers from late May through June. A second flush of flowers often appears in July or early August, especially if the old flower spikes are removed to prevent seeds from forming.
Vitex is an attractive plant with star-shaped, aromatic leaves that are grayish green on top and gray underneath. The natural shape is shrubby, but with some judicious pruning over time the plant can be trained into a delightful small tree. Mature height is about 10 to 15 feet with a spread of about 8 feet. Growth is rapid.
Rose of Sharon or althea
The fact that althea, Hibiscus syriacus, is a species of hibiscus is fairly obvious if you look at the flowers carefully. Like crape myrtles, altheas have a very long blooming season and come in a variety of colors. Flowering generally begins in May or early June and continues through the summer. Flower colors include white, pink, white with a red eye, lavender-blue, purple and light red and may be single or double. Like so many other traditional Southern plants, althea is native to Asia (so are gardenia, azalea and crape myrtle, to name a few).
This plant is commonly grown as an upright, large shrub or multi-trunked small tree. It generally grows 8 to 12 feet tall and 4 to 6 feet wide. It is deciduous, and unlike the tropical hibiscus (Hibiscus rosa-sinensis, another great shrub for summer color), it is perfectly hardy throughout Louisiana.
Another species of hibiscus that produces a long season of summer flowers is a type of the Confederate rose (Hibiscus mutabilis). You may be familiar with the traditional double Confederate roses that bloom in the fall. Exquisitely beautiful, the flowers open white or pale pink and change to dark pink/light red by evening (the species name, mutabilis, means changing and refers to the changing flower color).
For summer blooms, however, you want the form called rubra. This plant produces single, light red flowers all summer from May to October. Like all of the Confederate roses, rubra grows to be a large plant easily reaching 8 to 10 feet or more. Numerous shoots from the base give the plant a shrubby look. This plant drops its leaves in the winter, and although they may be killed back slightly or to the ground depending on how cold it gets, they reliably regrow each year.
Whiteflies are a major pest, along with the sooty mold they cause. One treatment of the insecticide imidacloprid in the spring when they leaf out will prevent whiteflies all summer.
What would summer in Louisiana be without our magnificent oleanders? These massive shrubs (10-12 feet tall and wide) produce masses of star-shaped flowers in shades of red, pink, white, peach, salmon and pale yellow. Dwarf oleanders reach about 5 feet by 5 feet and are available in pink and salmon.
If the winter is mild, blooming commences in April and occurs in several flushes through the summer. Although typically grown as a shrub, the plant’s large size lends itself to pruning into tree form in milder areas of the state.
Oleanders are evergreen, drought-tolerant and virtually carefree. They are prone to the small, white oleander scale insect, but this pest rarely causes major problems. It can be controlled with a light horticultural oil (such as Summit Year-Round Spray Oil) if needed. Although a surprising number of ornamental plants are poisonous, oleander is particularly toxic and should never be used around children’s play areas.
You can consider still more summer-blooming large shrubs and small trees for your landscape, including angel’s trumpets (Brugmansia and Datura, large, fragrant, trumpet-shaped flowers in mid- to late summer), harlequin glory bower (Clerodendrum trichotomum, a hardy, small tree that produces clusters of wonderfully fragrant white flowers in July), butterfly bush (Buddleia, a large-growing shrub with flower spikes in white, burgundy, pink and purple) and Southern magnolia (Magnolia grandiflora, especially the Little Gem, which repeat blooms until October).