I am quite taken with dwarf Gingkos and bought two last year, Chase Manhattan and Munchkin. I had expected Chase to grow about 1" a year and Munchkin about 1/2".. But Chase Manhattan has grown 14"' this spring and Munchkin 4". It's like they are both on steroids. I want to keep them small but I'm very hesitant to prune. Dare I?