Nothing says “summer” like a swath of brightly colored, blooming annuals. Over the past 20-plus summers in Charleston, I have tried a variety of annuals. Some work better than others. However, as Elizabeth Lawrence wrote, “... the failure of a plant in my garden does not mean that this plant will languish in all gardens in these parts.” (A Southern Garden, Univer sity of North Carolina Press, 1942).
Summer annuals, also called bedding plants, should be planted during April, after the risk of frost is past but early enough to establish before the temperature exceeds 86 degrees. Annuals can be replanted in late August to replace varieties that have “seen better days.”
Before transplanting, a teaspoon of slow-release fertilizer and a handful of compost should be mixed into the soil for each plant. Most annuals will need a dose of liquid fertilizer about two months after setting out and monthly after that. These summer annuals are the “best bets” most years.
Anthony Keinath is professor of plant pathology at the Clemson Coastal Research & Education Center in Charleston. His expertise is in diseases of vegetables. Contact him at email@example.com
Also called floss flower, ageratum has a cooling effect in the garden with its white, lavender or blue blossoms that some say look like powder puffs. This annual needs normal to moist soil. If it becomes too dry, ageratum wilts but recovers easily. It prefers afternoon shade, but I haven’t found the right balance of sun and shade to keep ageratum blooming continuously.
Commonly referred to as summer snapdragon, it is a drought-tolerant annual that tolerates moist soil. It has white, pink, raspberry or purple flowers in short spikes. As the name implies, it is kin to snapdragon. Angelonia must have eight hours of uninterrupted sunlight to bloom continuously.
This is a popular annual to grow in part shade. Combinations of green or red leaf color and white, pink or scarlet flower color are available. It prefers normal moisture but can tolerate short periods of wet or dry. The leaf color fades if wax begonia is planted in full sun.
Among the different types of gomphrena or globe amaranth, dwarf gomphrena is the one used as a bedding plant. This drought-tolerant annual for full or part sun has white or magenta flowers made up of a cluster of tiny petals as dry as paper. It needs no extra fertilizer.
Madagascar periwinkle or vinca is one of the best drought-tolerant summer annuals for the Lowcountry. It excels in sunny spots in normal to dry soil. The previous color range of white, pink and lavender now includes apricot, almost red and two-toned flowers. New spreading or trailing forms work well in pots and hanging baskets. This annual’s downfall is crown or root rot in overwatered or poorly drained soil or pots.
These traditional annuals are well-suited to the Lowcountry for early or late summer planting, but those planted in spring may not last until fall. The rust-and-orange colors of French dwarf marigold are classic, but I prefer the pure yellow and almost white cultivars. Marigolds enjoy composted poultry manure as fertilizer. In early spring, slugs may devour small plants. In my experience, a short cup or can buried to the lip in the ground and filled with cheap beer is the best way to catch and eliminate slugs.
Melampodium has broad, light green leaves and small, golden yellow daisy-like flowers. This tough annual is fairly drought-tolerant, but it will wilt if it gets too dry. Some cultivars, like the popular ‘Million Gold,’ will reseed.
I think pentas are one of the most attractive summer annuals, especially the pure white and pure red ones. The slightly rounded flower heads make perfect perches for butterflies. Pentas need regular watering after planting, but once the roots are established, the plants quickly recover from wilting.
Hybrid zinnia (Zinnia marylandica) was bred to resist powdery mildew, which often afflicts common zinnia (Zinnia elegans). Some gardeners may be familiar with ‘Profusion’ zinnia, one of the first hybrids. These tough plants bloom all summer. Fading flower color in mid-summer means the plants need fertilizing.
Others, with reservations
Not every plant can be a star. Some summer annuals are more likely to have problems than others. A common reason for decline is root rot, a disease that starts in soil that stays too wet during rainy summers. Fortunately, the NOAA three-month climate outlook calls for normal rainfall from June to August, so any of the recommended annuals mentioned previously should do well this year (www.cpc.ncep.noaa.gov/products/predictions/90day/).According to the ASPCA (www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants), all of the annuals listed are safe for dogs and cats except begonias and Portulaca species. It’s time to plant annuals and get ready for summer.
Celosia or cockscomb are brightly colored annuals in yellow, orange, or magenta. To a plant pathologist, their extreme susceptibility to root-knot nematode is reason enough to pass on them.
Impatiens is a classic annual for shady spots. They have not been widely available in several years because impatiens downy mildew has been a problem for ornamental growers and homeowners as far south as Virginia. Although impatiens needs moist soil, even they can get root rot if they are overwatered.
When I was growing up, petunia was THE annual everyone in the Midwest planted. Those oid-fashioned cultivars are not heat-tolerant enough to survive the Lowcountry summer. Heat-tolerance was one reason the ‘Supertunia’ and ‘Wave’ series of modern hybrids were developed. Both of these are spreading or trailing cultivars that require space to roam.
Moss rose or portulaca (Portulaca grandifolia) and purslane (Portulaca umbraticola) are closely related. Moss rose has short, narrow leaves and double flowers, while purslane has wider, rounded leaves, like the purslane weed (Portulaca oleracea), and larger flowers with a single layer of petals. The thick leaves and stems store water and allow the plants to tolerate dry soil. Although the flowers need full sun to open, new moss rose cultivars bloom on partly cloudy days. These annuals may not survive periods of heavy rain.
Scarlet sage or annual salvia (Salvia splendens) is prone to root rot. Affected plants drop most of their leaves, leaving bare stems topped with a tuft of small flowers. Their best attribute is the intense color of the ivory, scarlet or purple flowers.
‘Victoria’ mealy-cup sage (Salvia farinacea) is an old favorite with its royal blue flowers on dark blue stalks. This salvia often survives the winter into a second year. When plants or flower spikes are noticeably shorter than previously, it means the plants have root rot. Mealy-cup sage also is susceptible to powdery mildew that appears in early spring and late fall. Several sprays with potassium bicarbonate usually eliminate most of the mildew.