If they are already between 5 and 8 feet tall, why did you feed them? Sounds like the soil is good.
Once your area starts to lose the summer sun, they will go into flower and get even taller. I don't think I'd give anything from here on out except water, which should probably be more than a gallon if they are in the ground and if it's hot in your area. Should be monsters by the time their done. Some of these plants can grow to 20 feet outdoors.