"There is nothing to cultivate."
Translation:Non c'è niente da coltivare.
I've heard that one way to think about it is that you use 'di' to signify a characteristic whereas 'da' signifies a use or intention. Roughly speaking, if you could translate the preposition as 'with', you would use 'di', but if as 'for', you would use 'da'. Hence, 'carte di credito' = 'card with credit' (the credit is a characteristic or feature of the card), but 'niente da coltivare' = nothing for cultivating (very rough and awkward translation, I know, but hopefully helpful - the point is that cultivating is not a characteristic of nothing).