I'm running into a slight grass problem where I planted my blueberry bushes, and was wondering how thick I should make my coffee ground mulch around the blueberry bushes to prevent the grass from coming up.
I'd be careful on how much of the mulch consisted of the spent coffee grounds. They are a great soil amendment, but if they aren't mixed with soil or another mulch they may dry and then cake up. This may repel water absorption of the roots directly below them. I would mix it with the soil a bit then have another mulch on top of that. Just be careful not to disturb the roots. You might even be better off just getting soil/peat/compost/mulch and mixing it with the grounds instead of cultivating the soil under the bush.
I don't have an answer on an alternative mulch for weeding grass. I am currently using pine straw with peat with a few dead leaves 1 - 3 inches total (some are shredded and some are not), but still have mixed results. The centipede and Bermuda (Devil's grass) I have still tends to get under the bushes, but I add a little more leaves after harvest and then in Jan/Feb.
Still envious of your soil :) I have the sandy soil that I'm trying to build up.