I have a problem with grass not growing under a red mulberry tree. At first I thought it was too shady but tried a mix of rye and grass designed for shade. The rye came up but the other grass did not. It has been adequately watered. I'm beginning to think all those years of mulberry fruit dropping on the ground has made the ground too acid. Any thoughts?

kendahlin-
The shade is the problem. The fruit dropping is great for the soil. Unless you are geting 4-6 hours of sunlight under your tree you will not be successful with any of our desired grasses. Cut your losses and switch to a ground cover or mulch.
Tony M

Since you don't say where you are, I'm going to assume you're in Texas. Forget about northern grasses and put St Augustine in. It will grow in nearly full shade. Otherwise, go with ground cover. We have Asiatic jasmine that is doing great and never been watered in 10 years.