I have a group of about 12 Homestead verbena that have spread out all over the place. They have quit blooming and look scragly in the centers, but the runners are still very green and healthy and invading the adjoining plants. I want them to come back next year, but I would like to cut them back now so that I can plant a bunch of daffodils in among them. Will I hurt the verbena if I cut it back now? How much to cut? I'm thinking I'll leave about 6-8 inchs on each one, that way I'll have plenty of room to plant my daffodils. When is the correct time to cut it back anyway? Thanks!