|Last year I moved from the midwest to San Jose California, where the winters are mild. My coreopsis and Marguerite daisies do not freeze back or die down in the winter and they are getting way too big. I don't know when or how far to cut them back to control the size of the plants next summer. I'm used to a hard winter climate and have never had perennials that grew right through winter!|
|Marguerite daisies are treated as annuals in other gardening regions, but can 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 make 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 southern California climate!