in order to keep my blueberries acidic ( or at least I hope its working... as I have not been doing it long enough yet to know for sure, only a year) I contacted a local coffee roaster and he saves the bean chaff that falls off the coffee beans during the roasting process , its awesome mulch!!! I put it down then lay straw over it to keep it down. and it smells like coffee when it rains! Had an awesome crop this year and the plants seem to look healthy . Its free and he was already throwing it away! He just leaves garbage bags of it outside the back, if I don't pick it up it goes to the dump! Sometimes it has full raw beans and roasted beans mixed in, probably from sweeping the floor of the shop . no coffee plants have popped up yet though, but I'm always hoping To see one pop up lol;)
