Answer: Coreopsis are perennials that grow from one to two feet tall and spread about 3' wide. At the end of the season you should cut back the stems and foliage and remove the debris from the garden. In the spring new growth will sprout and the plant will get larger each year it's in the ground. After a few years you'll want to dig the roots and divide the plant. If flower heads are left on the plant after they dry they may release seeds which will germinate the following spring. This is okay if you want lots of Coreopsis plants, but you may not appreciate this self-sowing if your beds are very neat and tidy because you'll have many new plants in places you may not want them! It's a good idea to keep spent flowers cut back all through the season to encourage the plant to produce more flowers. Cut everything down to the ground now and dispose of it. When your Coreopsis sprouts next spring, regularly cut the old flowers and their stems back to keep more flowers coming. Then, after frost nips the foliage, cut it down to the ground and remove it from the garden.
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