I use fruit tree fertilizer made by Fertilome. I havent used the spikes but I would think they would work well. They are slow release so if you want faster growth you might be better off with a water soluable fertilizer. I fertilize weekly, sometimes more often. I alternate organic fertilizer (dried checken manure), granular fruit tree fertilizer and water soluable banana fuel. It seems to work well for me. My Basjoos were 15 feet tall at the end of the growing season last fall. One is already 10 feet, way ahead of this time last year. It helps that we had an early spring and warmer than normal temps this spring.