Sadly underutilized, C. palustris ‘Summer Sunshine’ was the highest-rated perennial coreopsis in Mt. Cuba Center’s trial. Vigorous plants grew to a height of 30 inches and bloomed for six weeks starting in late September.
Interest in native plants, such as Coreopsis, continues to surge as gardeners realize their benefits. Breeders respond with a dizzying array of new cultivars, but which one is right for you? A research report issued in December 2015 by Mt. Cuba Center can help you decide. They trialed 67 different varieties of perennial coreopsis over a three-year period, and after speaking with George Coombs, research horticulturist at Mt. Cuba Center, it’s clear that only the toughest survived.
None of the plants were coddled, because the average gardener doesn’t have time for that. They weren’t staked, sprayed, or fertilized. Winter hardiness was an issue; not because of temperature, but because Coreopsis prefer a sandy, well-drained soil, and the soil at Mt. Cuba is loamy clay. Mostly, it was the clumping types that perished; the rhizomatous ones were more adaptable. Another source of causalities was a wet summer – 12 inches of rain in June – that caused widespread root rot followed by disease.
The top four varieties that not only survived, but thrived, under these adverse conditions are listed in the quick facts or the photo captions. You can read the entire report on Mt. Cuba’s website, mtcubacenter.org. And if you have well-drained soil, consider some of the varieties that scored well, but didn’t survive a winter. For instance, ‘Mercury Rising’ died in Mt. Cuba’s trials, but it’s a winner in my garden. It’s all about your soil and picking the Coreopsis that’s right for you.
C. verticillata ‘Zagreb’ garnered fourth place at the trials.
Beginning in June, bright yellow flowers carpeted the 20-inch tall plants.
Common Name: Tickseed
Botanical Name: Coreopsis
Cultivars to Look For: Coreopsis tripteris ‘Flower Tower’ took second place in the trial. In August, sturdy, 8-inch-tall stems are topped with cheerful yellow flowers that measure 2½ inches across, the largest flower in the trial. C. tripteris ‘Gold Standard’ took third place, but many not be available at nurseries for several years.
Zones: Vary for different species, often 4-9
Type: Some are annual, but this article focuses on perennial Coreopsis.
Exposure: Full sun for all but C. latifolia, which prefers shade or part shade.
Soil: Well-drained soil is best, but rhizomatous types adapt to clay soils.
Watering: After their first year, trial plants survived on rainfall alone.
When to Prune: In late winter, cut to the ground.
In Your Landscape: Plant a pollinator garden with a variety of Coreopsis to extend the bloom season and support a great diversity of pollinators.
A version of this article appeared in Alabama Gardener Volume 15 Number 4.
Photography courtesy of Mt. Cuba Center.