I am not sure about fertilizer this time of year. Go to Google and type in growing blackberries, you can get better info from there than I can give you. They will also show how to build a trellis. Our first picking was Wed. Guess I should plant a acre of them, two women have called and requested all the berries we will have this year. In case you forgot they are Triple Crown. Can have you more plants next spring, just be sure and remind me as I am having problems with my memory and age is not helping. My writing is terrible and you a school teacher, please don't fail me for trying to answer you.
Norm