I'd apply in moderation. Basically, don't throw several pounds of grounds into a 5-gallon bucket. Coffee grounds are acidic and high in nitrogen (which are both good) but you don't want to get into "too much of a good thing".What effect will coffee grounds have on my strawberries and raspberry plants? I've got the living in 5-gallon buckets until the weather gets better. Will tossing the grounds on them benefit or hurt?
I spread my grounds out in the garden and don't recall ever using them in a potting situation.