In addition to plumbago and lantana, most Charleston gardeners are looking for more summer flowers that can take the heat and humidity of August.
Here are some perennials that are well-adapted to the Lowcountry and bloom during the heat of summer. (I will cover summer-blooming annuals in a future column.)
Even if your garden isn't a tropical paradise, adding three tropical perennials - ginger, canna and hibiscus - to your plantings will definitely improve the flower-to-foliage ratio.
Of the three tropicals, gingers are my favorite, especially gingers in the botanical genus Hedychium. Their large, broad leaves add a coarse texture to the landscape.
Hedychium flowers start as a green "cone" or compressed, compound flower. Individual flowers emerge between the layers of the cone and usually bloom one after another.
Butterfly ginger, one of the most common gingers, is a Southern Living "Southern heritage" plant. The pure white blossoms have a sweet fragrance that reminds me of gardenia. Butterfly ginger spreads to form a loose clump of plants.
Most Hedychium gingers have flowers in various shades of cream or yellow. Be aware that cultivars promising darker colors, like raspberry, may have flowers that are closer to salmon pink instead.
A second type of flower in Hedychium looks like a bottlebrush. These cultivars also produce a flower cone, but all of the individual flowers in a cone open at once. A cultivar like "Disney Orange" (also called "Orange Bottlebrush") is a true "show stopper" when it blooms in the August garden.
A tip I learned at a local garden center was to add peat moss to soil when planting gingers. Peat moss helps to create an ideal moist but well-drained soil. Use about 2 to 3 cups with a 3-quart or 1-gallon pot.
Canna (Canna species) is a dependable perennial for the Lowcountry. Its main advantages are a long blooming time that includes August and tolerance of wet soil. Cannas and gingers, both 4 to 5 feet high, are good backdrops for shorter flowers with small, round leaves or long narrow leaves, like swamp crinum.
Cannas are used to absorb excess fertilizer in the water that drains from commercial production nurseries. They can serve the same purpose in home yards if they are planted near drainage areas; see the Carolina Yards guidelines at http://bit.ly/1uE5T7W for more information.
The one drawback of canna is the canna leafroller. Young canna leaves are rolled up, and, if this caterpillar invades them, they do not unroll properly. Canna leafroller damage makes leaves look "ratty," i.e., torn and yellow. Flowers may not even open.
Biological insecticides can't reach canna leafrollers inside rolled-up leaves. The solution is to apply a systemic insecticide that is absorbed by plants, so when the leafroller eats the leaves, it dies.
Red-leaved cannas are particularly attractive to gardeners and the canna leafroller; these cultivars likely will need insecticide. Because green cannas are less susceptible, cleaning up all leaves after they freeze may eliminate leaf-rollers and make the insecticide unnecessary.
There are three hibiscuses that are useful in Lowcountry gardens in August. (Note that the first two are not deer-resistant, but the last one is.)
Chinese hibiscus (Hibiscus rosa-sinensis) is a frost-sensitive perennial, although it will survive planted in the ground in USDA Zone 9, an area centered on Charleston Harbor (planthardiness.ars.usda.gov). The single or double flowers come in a variety of warm colors. Flowers last only one or two days, but new ones open every day. Chinese hibiscus tolerates part shade, although it will not produce as many flowers as it does in full sun. It needs regular watering if grown in a pot.
Texas red star hibiscus (Hibiscus coccineus) is a tall native plant that also prefers moist soil. Because it can reach 7 feet tall, its natural place is in the back of a bed. As its name implies, the flowers are rosy red with five petals. It blooms best in full sun.
Rose of Sharon (Hibiscus syriacus) is a woody shrub with a wide growing range (USDA zones 5 to 9). The flowers on different cultivars are white, various shades of pink, or bluish purple. Most cultivars reach 8 feet, but a few dwarf cultivars stay 4 feet. Rose of Sharon blooms summer to fall.
Balloonflower (Platycodon grandiflorus) does not usually come to mind as an August bloomer. However, it was rated as a good bloomer in two of the three years I tracked the best summer bloomers in my yard. Blossoms are big enough (1½ to 2 inches in diameter) to be visible 25 feet away, so even a few plants will add impact.
If the flowers are deadheaded by removing the round seed pods, plants will rebloom several times, although with fewer flowers. The cultivar 'Mariesii' is a better rebloomer than 'Sentimental Blue.''
Three salvias are champion summer bloomers. Bog sage (Salvia uliginosa) flowers from May through August.
The related pair of salvias, 'Indigo Spires' and 'Mystic Spires,' are some of the most prolific summer-blooming perennials I grow. Both are crosses of Salvia longispicata by Salvia farinosa (mealy-cup sage). 'Indigo Spires' gets its size, a good 4 feet tall and wide, from Salvia longispicata. 'Mystic Spires,' is only 18 inches tall and wide, not counting the 12-inch flower spikes.
Garlic chives (Allium tuberosum) start blooming in August every year. This herb is closely related to common onion chives. Garlic chives have flat clusters of white flowers that attract butterflies and beneficial insects. Garlic chives need part to full sun and water during dry periods. They can be found in the herb sections of local nurseries. It is easy to get more garlic chives by leaving spent flowers on plants to drop their seeds.
Bloodflower milkweed (Asclepias curassavica), a frost-sensitive, summer-blooming perennial, is a welcome addition to any garden, since it is food for monarch butterfly larvae. Plants with flowers in yellow or orange red are widely available. If caterpillars don't eat all of the flowers, bloodflower milkweed may self-sow, but these seedlings rarely come up early enough to bloom. In addition to monarchs, bloodflower milkweed attracts beneficial insects and bright yellow aphids. Insecticidal soap can be used to control them.
Finally, based on the season or how much sunlight plants get, August may have late or early bloomers to add to the number of flowering plants. For example, black-eyed Susan grown in part sun will bloom later than in full sun, so it still may be flowering in August. Likewise, Mexican bush salvia in full sun often starts blooming in late August.
By planting several of these consistent bloomers, Lowcountry gardeners can enjoy flowers throughout the summer.
Anthony Keinath is professor of plant pathology at the Clemson Coastal Research & Education Center in Charleston. His expertise is in diseases of vegetables. He also is an avid gardener. Contact him at firstname.lastname@example.org.