My wife and I are hoping to close on some land we are buying outside of Crossville, TN on the Cumberland plateau. It's elevation is 1900 feet and it is in zone 6a. We won't be able to move onto the land for another five years, so I was thinking about planting some trees and giving them a "head start." The problem is that we won't be there to tend to them until I retire in five years. Are there any fruit trees/bushes/plants that grow well if left untended for an extended period of time?

We haven't had the soil tested yet, but I think it will be pretty to very acidic judging from the broom sedge growing on it and the soil survey that is on this website. https://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

Thanks!

If you don't mind "wild" there are a lot of things. Research the native species that grow in your area that provide fruit/nuts. I am in 6B and for us those are blackberry, black walnut, black cherry, some forms of raspberry, wild strawberry, elderberry both red and black, white oak, chokecherry.

If this is completely no tend then look to spend some time originally cutting out invasive species that could overwhelm the ecosystem and cause natives to struggle. Best of luck!

Several trees come to mind. 

Persimmon is native to the eastern US. They produce edible fruit, and they have a deep tap root that will draw minerals from the sub soil. 

At one time I lived in Blacksburg Virginia.  I remember seeing many black cherries going wild there.  I would think they would do well on the Cumberland plateau.

black locust is another eastern US native.  It doesn't produce any edible fruit but it is a nitrogen fixer and the wood is very tough.  It is often used for fence posts here.