fertilizing banyan trees?

[My 2 cents]

A weed is just a plant out of place. In my list of attributes for banyans I neglected to mention that they can also be quite beautiful and majestic. It's possible that you have a place that is suitable for a banyan to exhibit these qualities. I urge you to think it through and consider the work you might be creating for yourself but, having said that, if you do decide to cultivate it then my answer to your original question remains the same. It will gobble up anything you want to feed it, but there is no need to.

Good luck!