How to Grow Coreopsis
Coreopsis flowers are attractive to butterflies, and the leaves to the caterpillars of some butterfly species.
About half the 80 or so species of coreopsis are native to North America, the rest native in South America. Keep this in mind if you’re choosing coreopsis for native plant gardens to help support wildlife and the overall ecology of your landscape.
When & Where to Plant Coreopsis
Light: While coreopsis generally will survive with less than full sun, it may bloom poorly if at all. Plant where it will get at least 6 to 8 hours of full sun daily. An exception is the broad-leaved tickseed (latifolia) which prefers part to full shade.
Soil: Coreopsis prefers well-drained soils and, once established, even may tolerate droughty soils. Some such as the threadleaf coreopsis will tolerate dry, rocky soils. What they don’t like are heavy, wet soils. This will affect their winter survival. Clay and wet soils can be amended with compost, or beds raised with better soil on top. Species that creep, rather than form clumps, are better able to overwinter on heavy wet soils.
Spacing: While this varies with the species and cultivar, generally 12 to 18 inches apart will work for most.
Planting: Since these are usually found in pots, you can plant the perennial ones most anytime, from early spring (they may tolerate light frost) through early fall. Plant the annual ones in spring to enjoy their bloom throughout the season.
How to Grow Coreopsis Throughout the Season
Growth Habit: Coreopsis form upright clumps, and have a moderate growth rate.
Staking: Staking is generally not needed, as plants tend to only be a foot to 18-inches high. For those getting taller, or ones which get taller from growing in part shade, you may need to put a “hoop” type cage around them in mid to late spring.
Watering: Keep well-watered after planting (water deeply every few days). Once established, they may only need water if wilting, or prolonged droughts—most types will tolerate some drought.
Fertilizing: Fertilize with your choice of synthetic or organic fertilizer, at normal rates according to package directions. Coreopsis don’t need much fertilizer and, in fact, too much may make them too tall with all leaves and no flowers. If soils are already good, a side-dressing of compost in the spring may be all that is needed.
Trimming & Pruning: Deadheading (removing spent flowers) helps promote more blooms later. If there are many dead blooms, you can shear them off with scissors or grass clippers. Cut plants back by one-quarter to one-half to keep a tidy habit, and to have a better chance of late season bloom.
Mulching: You can add 2- to 4-inches of an organic mulch such as bark or straw around (not over) plants in early spring to help conserve soil moisture, moderate soil temperatures, and to deter weed seeds germinating.
Coreopsis: End of Season Care
After several heavy frosts, in mid to late fall cut perennial selections back for winter, leaving a couple inches of stems at the base. This helps to protect the “crowns”, often which have basal growth there already, ready for next spring. Avoid cutting back too early in fall to allow birds such as goldfinches to enjoy their seeds. Annual varieties, killed by frost, can be removed and composted (unless they have pests or are diseased).
Dividing & Transplanting: For perennial coreopsis, if they begin looking weak with fewer flowers after three years or so, divide them if needed in spring or early fall. Dig plants, use hand tools to divide into smaller sections, then once replanted keep well-watered until established and growing—several weeks.
Pests/Disease: Coreopsis are a low-maintenance plant, generally with few if any pests or diseases. If you see aphids on stems, just wash off with a forceful stream of water. If plants are starting to rot at the base (crown), chances are they are staying too wet. If this is the case, dig and move plants to a drier site.
Some of those with broader leaves may get the whitish powdery mildew which is more of a cosmetic nuisance than harm to the plant.
If you want to prevent this from spreading, use labeled sprays, several choices being organic, starting when you first see this disease. Unlike most diseases, powdery mildew doesn’t need moisture on leaves to infect them—warm, dry weather suits it just fine.
Additional Concerns:
Make sure when buying coreopsis to note their hardiness rating on the label or in descriptions,and whether they are grown in your area as an annual (one year) or perennial.
If you find that you have a coreopsis that is spreading vigorously in your garden through its underground stems (rhizomes), just keep it in check each spring with a shovel or hoe. Another option, if other perennials won’t be overrun, is to just let it go to form a colorful mass planting.
Coreopsis: Extra Info
Propagation: Want more coreopsis? You can divide them in spring or early fall, with a minimum of several shoots or growing points per division. Some, including the annuals and perennial species, you can start yourself from seeds which should germinate in two to three weeks.
If you don’t sow directly in the garden in early spring, start indoors 6 to 8 weeks before the last frost. Don’t cover the seeds, as they need light for germination. As with all seed sowing, use a sowing medium such as one containing peat moss and perlite, keep warm (70 degrees F or so), and moist.
Companion Plants: Coreopsis combines well with shasta daisies, daylilies, Helen's flower, blue mist shrub, speedwells, blanket flower, perennial salvia, lavender, Russian stonecrop or Autumn stonecrops. Use it along border edges, in masses, along walks, in cottage gardens, in small groups or singly in rock gardens. Annual varieties which self sow are particularly suited to, and often a component of, wildflower seed mixes.
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