I am growing WW and Hindu Kush in FFOF soil.I thought that I wouldn't need the Grow big fert because OF is pretty rich. I am sure that I will have to give them a substantial source of N seeing as they are getting pretty big.What can I give them as a N source as I am sure they will need it sometime soon. They have been on 12/12 for 4 days and are 6 weeks old.