Coreopsis maritima – Sea dahlia

Question from Melanie:
I have several plants of coreopsis maritima which bloomed brilliantly last spring. Now, in summer, they are dormant and dead looking. Should I prune them back or leave them as is? Thanks for your help.

Answer from Pat:
Sea Dahlia (Coreopsis maritima) is a flowering shrub native to the San Diego County seacoast and into the northern Baha California. Its large flowers —5-inch-across—blooming in late winter and early spring, are bright, vibrant yellow and resemble dahlias held on long stems above the foliage. The foliage itself is coarser than its close-relative, giant coreopsis (C. gigantea) which has feathery foliage, and is native to a larger swathe of the California coast—from Los Angeles through San Luis Obisbo Counties and Guadalupe and the Channel Islands and grows to a stunning height of five or six feet.

Both of these plants detest summer irrigation but watering giant coreopsis in summer is more likely to be fatal than summer watering of sea dahlia. Both plants have fleshy roots, but those of giant coreopsis are more prone to rot. Sea dahlia (Coreopsis maritima) can bloom all summer long if deadheaded, grown in fast-draining soil, and watered sparingly. The fact that Coreopsis maritima can be deadheaded without killing the plant tells us that it can be pruned but not too much. It sounds as if you are growing sea dahlia as it would grow in nature—totally dry in summer except for an occasional spritz of rain. This is far safer. I know since I once killed a sea dahlia by watering it in summer even though it was growing in sandy soil.

Left to nature, Coreopsis maritima’s foliage and flowers will fade in late spring and the appearance of the shrub may be messy in a home garden. The correct amount of pruning to do is more like a strong wind might do in nature. Once the flowers have faded, cut these off at the base of their long stems. Once the foliage has shriveled until its crisp and dry, you can simply pull it off the stems with your gloved hand and clip off those that still hang tight. If after doing this you see some dead wood, this may be clipped off too. Beyond this treatment, I would leave the bare woody structure of the plant untouched during summer. Don’t cut it back or you risk killing the plant. You will probably find that without its messy hair of dead flower stems and beard of dried foliage, the plant in bare dormancy is sufficiently statuesque to please yourself and anyone else who sees it or at least it will blend in and be unnoticed in a landscape of succulents or wherever you might be growing it.

Any other pruning to shape the plant should only be done in fall after rains have begun and the plant has resumed growth, but usually no pruning is necessary. Both sea dalia (Coreopsis maritima) and giant coreopsis (C. gigantea) have fleshy, succulent wood that they need in summer to tide the plant over during summer dormancy. Part of the pleasure of these plants is the windblown form they eventually develop. The branches often curl at the tips as they dry out. Let them be. They will plump up and straighten out when rains return. Cutting into this wood in spring or early summer might cause rot. Also, as soon as rains begin in fall the bare branches will awaken and spring to life, pushing out new green leaves and soon after will arise the flowers.