It is time to begin thinking about cool-season bedding plants for the fall and winter landscape, and dianthus deserve some increased attention. Most of us are very familiar with garden mums we use for fall color during September, October and November in Louisiana. Also, pansies are familiar to most of us – as they should be – since they are the most widely planted cool-season bedding plant. But new dianthus varieties make this lesser-known plant deserving of attention.
The cool-season dianthus has long gone by the scientific name Dianthus chinensis. Now new hybrids and species are making dianthus an excellent choice for winter and spring landscape color. A new hybrid group is a cross between Dianthus chinensis and Dianthus barbatus, and Dianthus barbatus by itself is the source of some great-performing new varieties. These new species and hybrids are taller growing and have potential as cut flowers.
The "Telstar" series of dianthus is a former Louisiana Select plant and is one of the best cool-season bedding plants for the South. Individual plants reach 12 inches tall in the landscape and bear clove-scented flowers about an inch-and-a-half across. This series has good heat tolerance, so it will last until late spring. Numerous flower colors are available in the series, and you are guaranteed success whether you choose to use them in a landscape bed or container.
The dianthus getting the most attention the last 5 years or so is "Purple Bouquet." Flowers are not truly purple – they are more of a hot pinkish purple. "Purple Bouquet" is on the Dianthus barbatus interspecific hybrids and is a Mississippi Medallion plant. It also has been an outstanding in our LSU AgCenter landscape plant evaluations. "Purple Bouquet" dianthus reaches heights of about 24-30 inches and blooms last longer into the warm-season heat and humidity when compared to other varieties. Other varieties to try include the Ideal and Floral Lace series. "Melody Pink" is similar in growth habit to "Purple Bouquet." In addition, you may want to try "Corona Cherry Magic," a recent All-America Selection. The "Amazon" series is another great group of dianthus.
Dianthus perform best in full sunlight but also do okay in some filtered afternoon shade. Landscape beds need to be loose, well-drained and fertile. Dianthus do well at a slightly acid to slightly alkaline soil pH. Dianthus do not tolerate wet soil conditions, so it is important to adequately prepare a landscape bed and irrigate properly. Plant during October or November on a 10- to 12-inch spacing to achieve a full landscape effect. At planting, or shortly thereafter, broadcast an application of a slow-release fertilizer over the entire bed area. Depending on plant performance, a second, light application may be beneficial in early spring. Dianthus usually last well until mid- or late spring in the Baton Rouge area. Although dianthus are a perennial plant, they probably will perform best when treated as an annual, cool-season plant from mid-fall through late spring. Replace dianthus with heat-loving annuals in May.