blomma wrote: I cut all my perennials down to soil lever after blooming. I am in zone 4 and have never lost a plant by cutting down. I like to see my borders neat. Also raking is easier without dead plants in the way. I don't have time to cut back in the Spring. I do still have to do some tiding up but that goes faster. Actually, I enjoy cleaning up. The sun is out and temp is not so high.
I used to grow a Butterfly Bush. It is recommended to trim it back to 1" above soil. That is what I did.
Hardy mum I cut down to ground level also.
Consider also that bug finds a nice hiding place in dead plant material. Likewise disease.