HARDINESS: Zones 4 to 9
PREFERRED SOIL pH: Neutral to slightly acid
PREFERRED SOIL TYPE: Average
PREFERRED LIGHT: Sun
ATTRIBUTES: Yellow or pink flowers; mounds of ferny foliage; for beds, pots
SEASON OF INTEREST: Summer to fall
FAVORITES: 'Early Sunrise', 'Moonbeam', 'Rosea'
QUIRKS: Campanula, larkspur, Russian sage, rudbeckia, Shirley poppies
GOOD NEIGHBORS: Grows best when clumps become crowded
WHERE IT GROWS BEST: Full sun, average soil
POTENTIAL PROBLEMS: Root rot can develop in wet winter soil
RENEWING PLANTS: Lives many years; divide clumps as desired
CRITTER RESISTANCE: Good
DIMENSIONS: 1-3 ft (0.3-1 m) tall and wide
Coreopsis in the Landscape
Sunny yellow blossoms are the hallmark of native North American coreopsis. This is a varied group of plants ranging from the 4 ft (1.2 m) tall lanceleaf coreopsis (Coreopsis lanccolata), which should be a resident in every wildflower meadow, to several compact modern counterparts that stand less than 18 in (45.7 cm) tall. All are among the most dependable summer-flowering perennials you can grow.
The yellow flowers combine beautifully with soft blues and pinks, but you may need to experiment to find companions that share the same bloom time. In Zones 7 to 9 coreopsis remains green through winter and blooms in late spring, along with fall-sown larkspur, Shirley poppies, and roses. Where winters are colder and coreopsis holds its new growth until spring, mix them with mid- to late-season bloomers such as campanula or pastel-flowered yarrow, or set them against a background of Russian sage.
Some coreopsis cultivars come in neat garden-sized packages. C. verticillata 'Moonbeam' stands 18 in (45.7 cm) tall. Its airy, threadlike foliage is topped by petite, 1 in (2.5 cm) wide, pale yellow, daisy-shaped flowers. C. grandiflora 'Early Sunrise' has yellow semi-double blossoms held on stiff, 16 in (40.6 cm) tall stems. Shorter still is C. auriculata 'Nana', with 1-2 in (2.5-5.1 cm) yellow-orange flowers topping 12 in (30.5 m) tall plants.
C. verticillata 'Rosea' adds pale rose flowers to the spectrum. At 15 in (38 cm) tall, 'Rosea' requires supplemental watering in hot, dry weather. If grown in favorable conditions, it makes a handsome groundcover.
Coreopsis will survive in poor, dry soil, but it produces more flowers if given regular water and a little organic or controlled-release fertilizer each spring. However, once it's well established, coreopsis won't perish in a drought. If you garden in an area with wet winters, be sure to plant it in well-drained soil to prevent root rot. Deadheading, or removing spent flowers, keeps the plants neat and encourages re-blooming. Insects rarely visit, but the occasional aphid can be knocked off with a spray of water from a hose. Remove weeds and garden debris to discourage nesting places for insect pests.
If you encourage coreopsis to grow into small colonies, they will practically take care of themselves. To increase your supply or rejuvenate old clumps, divide plants in late summer using a stout knife. Locate a tuft of foliage growing outside the mother plant, cut a circle around it to take out a few roots with the surrounding soil, and lift it Out of the ground with the knife blade. Replant right away so that it will be well rooted by spring.