Search this forum for Arundo. There was a long thread about it which included information from a member who used lawn ferts for his, and they were gargantuan.

Arundo is huge on its own. I wouldn't fertilize it unless you want it to eat the yard.

In fact, I stopped fertilizing all my grasses and have found that they are more sturdy and more likely to stand upright.

I also am very stingy with water -- maximum once or twice during our normally dry summers.