Aphrodite althea in full bloom (Photo by Dan Gill)

Magnolia grandiflora Little Gem (Photo by Dan Gill)

Shoal Creek Vitex form (Photo by Dan Gill)

For Release On Or After 07/04/14

By Dan Gill
LSU AgCenter Horticulturist

For the summer season, no flowering tree or shrub out-blooms 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 late July or early August.

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. Shoal Creek vitex is a Louisiana Super Plants selection.

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 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 (as 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 and 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.

Confederate rose

Another species of hibiscus that produces a long season of summer flowers is a type of 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 Confederate roses, Rubra grows to be a large plant easily reaching 8 to 10 feet or more tall. Numerous shoots from the base give the plant a shrubby look. This plant drops its leaves in winter, and while it may be killed back slightly or to the ground depending on how cold the winter gets, it reliably regrows each year.

Whiteflies are a major pest along with the sooty mold they cause. One treatment of imidacloprid insecticide in the spring when they leaf out will prevent whiteflies all summer.

Oleander

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 colors.

If the winter is mild, blooming commences in April and occurs in several flushes through summer. Although typically grown as a shrub, their large size lends itself to pruning into tree form as well in milder areas of the state.

Oleanders are evergreen, drought tolerant and virtually care free. 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.

Magnolia

Little Gem magnolia is a dwarf mutation of the Southern magnolia (Magnolia grandiflora) that grows to be about 25 feet tall and 8 feet wide. This delightful tree has dark green, shiny foliage with rusty brown on the back. Fragrant, white flowers are produced from May through October. This tree is an excellent choice where a standard Southern magnolia would be too big.

There are still more summer blooming large shrubs and small trees to consider adding to 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) and butterfly bush, Buddleia, a large-growing shrub with flower spikes in white, burgundy, pink and purple.

Rick Bogren