Coreopsis – Tickseed: Coreopsis is one of the mainstays of the perennial garden because its golden yellow blossoms brighten the landscape from June until frost, even on the gloomiest days. An American native, hardy from zones 3 and 4 to 7 or 9 depending on the species, Coreopsis is usually found at the front of the border because most species grow only one to two feet high. Needing only full sun and well-drained soil, it is very drought-tolerant.
Coreopsis verticillata (Thread Leaf Tickseed) is the best known species and requires the least maintenance.Thread-like foliage bolsters its ability to withstand drought. The small single flowers, held on slender stalks, are very floriferous and an installation of five plants can appear to be a small yellow meadow. After the first flush has lost its petals, shear the whole planting by one-third. Within three weeks, another flush will appear. Each flush is usually in bloom for three to four weeks. If faithfully sheared on time, I normally have three flushes a year.
‘Moonbeam’, the Perennial Plant Association’s Perennial of the Year in 1992, is a clear lemon yellow that can be combined with almost any other perennial. ‘Golden Showers’ and ‘Zagreb’ are golden yellow so more care must be taken when working them into a design. ‘Zagreb’, the shortest cultivar, is 8-12 inches, while the other two can be 12-24 inches. A bit taller but extremely vigorous is the red/yellow bicolor ‘Rt.66’. ‘Sienna Sunset’ is a lovely apricot.
C. grandiflora and C. lanceolata (Large Flowered Tickseed) are virtually indistinguishable and require much more deadheading. A relatively new cultivar, ‘Tequila Sunrise,’ has variegated foliage.
Coreopsis is an excellent alternative to Rudbeckia. It combines well with ornamental grasses and perennials that have yellow variegation in their leaves and its length of bloom bridges the periods when other perennials come and go.