I leave the flowers on for a while,even though they have gone black..then I trim them back about halfway,when they look worse for wear..the old stems help protect the new growth which will appear in spring..and then I would cut them off..they are very hardy,Jmac,so you won't lose them..mine have been in for years. Are they the tall ones,or the shorter variety? If the latter,I would just take the dead flowers off....hope this helps,and welcome to Goy..:o)

I cut mine back to ground level, they grow like mad !!!!

I don't do mine until spring. the seeds feed the birds and they look pretty frosted too.