I planted this a couple years ago under the assumption it would be an annual for me, but it has now wintered over twice, so I think I can safely call this a perennial. Any suggestions on what to do with it in the fall? The last few years I let it go to seed and diligently gathered seed, thinking I'd need to replant it. But, that is apparently not the case. It has bulked up and still has some flowers but most have gone to seed. Should I trim it back to about a foot, cut it to the ground, or just let it sit for the birds? I'm in zone 8, Pacific NW - wet cold winters but no snow cover (occasional flurries but rarely anything that sticks around for any length of time). Thanks. I love the licorice fragrance.