Q&A: Pruning Coreopsis and Marguerite Daisies
Q: Last year I moved from the Midwest to San Jose, Calif., where winters are mild. My coreopsis and marguerite daisies don't freeze back or die down in the winter, and they are getting way too big. When and how far do they need to be cut back to control the size of the plants next summer? I'm used to a hard winter climate and have never had perennials that grow right through winter!
A: Marguerite daisies are treated as annuals in other gardening regions but become woody perennials in southern California, as you've discovered! It's best to pinch and prune the plants while they're young to keep them in shape. Since yours are overgrown, it may take a full growing season to gradually reduce the size of the plants without causing undo stress. Wait until early spring, just as new growth begins, and remove about one-third of the length of the stems. This will force new growth from below the cuts. During the growing season remove spent blooms and take some of the stems too. This will encourage bushy growth and will keep the height and width of the plant under control. You can reduce the size of your coreopsis in a similar manner. To keep the plants looking attractive, cut back the stems after the flowers are spent and new flowering stems will be produced lower down on the plant. Enjoy your new climate!
— National Gardening Association