I have never thought much about coreopsis until recently when I had some spaces to fill in the perennial border — and then I was faced with the fact that there are an awful lot of coreopses to choose from.
Even the name doesn’t inspire: The Greek “koris” means bedbug while “opsis” means to shear. Its common name, tickseed, also does not engender great enthusiasm.
However, don’t disregard these native plants because they can be workhorses in the garden — if you know which cultivar to choose. Fortunately, Mt. Cuba Center has issued a report on a three-year trial they conducted that you can find at mtcubacenter.org/trials/coreopsis.
Coreopsis for a long time was considered to be a short-lived plant. It was only in the 1990s with the introduction of the cultivar Moonbeam — also named Perennial Plant of the Year in 1992 — that coreopsis began to move into the main stream of gardening. Because of the growing interest in native plants and in those attracting pollinators, coreopsis is now here to stay.
In the Mt. Cuba trial that tested thirteen coreopsis species over three years, the clear winner was C. palustris Summer Sunshine — an interesting name considering that this coreopsis blooms in September for six straight weeks. The foliage is attractive, so consider this as a filler for the perennial border until it erupts into bloom.
Interestingly enough, C. Moonbeam, the 1992 perennial plant of the year, only received 3.5 out of 5 possible stars, demonstrating that hybridizers have made a lot of progress in the intervening quarter of a century. I planted another 3.5 star variety, C. Full Moon only to have it flop. Clearly, gardeners have better options now than to settle for a 3.5 rating when it comes to this genus.
Be aware that cultivars differ in height. One recommendation, C. tripteris Flower Tower soars at a majestic 8 feet in height, a height that will pose problems in most gardens. Another one, C. tripteris Gold Standard weighs in at a dainty 5.5 feet. Almost all of the recommendations spread via rhizomes — but very slowly, about 1-2 feet over two to three years.
Powdery mildew can be a problem with many coreopsis cultivars if the climatic conditions — warm days and cool nights — are present. Therefore, provide good air circulation around the plants but remember that the best preventative is to select a cultivar that is mildew resistant.
Do you want instant color but you’re not sure whether you want to offer a permanent home to coreopsis? The solution is to try the annual coreopses that have greatly improved since their popularity plummeted decades ago. They come in a wide range of colors that bloom all summer long.
Coreopsis’ reputation for being short-lived can be traced to the soil: This is a genus that needs well-draining soil, especially in winter.
Most of the clumping species, including C. auriculata, C. falcata, C. grandiflora and C. lanceolata did not survive the winter moisture in clay soils; the rhizomatous species, C. integrifolia, C. palustris and C. tripteris, among others, fared much better. Bear in mind that the rhizomatous species will spread — but will spread relatively slowly.
Coreopsis wants full sun and a well-draining soil. Because many cultivars could end up flopping — a dreaded event in my garden — this study is worth looking at before you make a purchase at your local garden center.
These plants are never going to be the star in the garden but they provide a lovely respite when the rest of the garden is getting tired as they bloom typically in later July and August. These plants are great fillers, ones that supply colors when the roses are crying for a rest, the day lilies have left us and the phlox is spent.
This is a valuable report. My advice is to read it and take notes as you have nothing to lose and a lot to gain.
Absent from their gardens, Kit and Lise enjoy roaming our region exploring the intersection of horticulture and suburban living. More on Instagram @AbsenteeGardener or email firstname.lastname@example.org.