Q. What's the best groundcover under fruit trees?
A. It kind of depends on how much water costs. If water is expensive, a living groundcover might not be the best idea.
|Farmer intercropping with sesame between fruit trees in Tajikistan|
Also, living groundcovers like alfalfa or clovers don't return as much nitrogen to the plant as people think. In fact, they usually compete with the plant for water and nutrients and don't return the benefits that people think they should.
In our arid and desert West, surface mulches are usually the best option. I like to see woodchips from local arborists or tree trimmers used around the base of the trees to a depth of 4 inches or more.
I have seen some inter-cropping when fruit trees are young with things like melons planted beneath them. This way at least you can get double duty in food production from the water that's being applied.
Remember that intercropping increases the amount of care required because you are growing crops you have to tend. Fruit trees that may not require visits more than once every two or three weeks now have melons planted beneath them that require visits of 2 to 3 times per week.
So if it were me, I would use a nonliving groundcover such as woodchips from local tree trimmers.