I always buy petunia bags to hang in the front of my house. I've never really done anything special with them other than water every day or every other. I'm wondering if I should be fertilizing them. I would certainly like them to last till the end of the season. 2 of the bags ( I have 4) are very scraggly and sparse. They are also very leggy. Should I be pruning these too? If so, how do I do that? Thank you in advance!