crowded flowers

I have such limited space for flowers that need full sun that too often I try to cram in more than I should.  I'm thinking my big yarrow plant in the front is going to have to go to make room for other things.   I've got a dahlia behind it that is definitely getting crowded and blocked from the sun.  Sigh.
I talked to a friend who lives up the street who will give it a new home.  At least there I can go visit on occasion.