Trying to grow grass under an oak tree is nearly impossible. Your soil will test to be highly acidic, probably in the 4.0-5.5 pH range. Vinegar runs about 4.0. Add the shade and heavy clay soil and you might just forget about it.
You will notice that the oak leaves do not decompose as they are contain high levels of tanic acid. Tanic acid is used in the tanning process to preserve leather. Clay soil is loaded with nutrients, but due to the the high acid content it does not allow them to become available to ground plants, grasses included.
If you are bound and determined to grow grass under the oak trees you might try applying 10 lbs. of pelletized gypsum (calcium sufate) per 100 sq. ft. to the surface along with decomposed organic humus (do not use peat moss as it is also very acidic), roto-till about 6” deep and find a shade loving type grass seed. The gypsum will break up the clay soil and allow it to breathe and allow the humus to mix with the highly nutritious clay soil and bring you pH up to acceptable levels.
The best and most available organic material is probably decomposed cow manure. Avoid horse or chicken manure because it is too rich in nitrogen and will most likely ‘burn’ your grass. It’ll grow like hell at first, but then turn brown and die off.
Have you thought about growing a ground cover like vinca minor (periwinkle) or sweet woodruff? There are many ground cover type plants that would do much better than grass and you don’t have to mow it! Remember that nature is as persitent as a spring and it will strive to return the area back to it’s original form.
If it were me, I’d let it just remain a forest setting and go fishing instead.
Just my opinion.
calcium sufate = calcium sulfate
That all sounds like good advise. My problem is being on a hill. Erosion has taken dirt from under the trees and we have roots above ground under the canopy. I would like to bring in dirt to cover the roots and plant something to hold the dirt in place, either a grass or ground cover. I am at a total loss because we moved here from a yard of full sun and all grass with only one mature pine tree on the property. It was alot of mowing, but no headaches.
Thank you for the info.
Anyway: isn't gypsum itself acidic and will contribute to acidity in the soil?
I put gypsum in my clay soil and it is not conducive to low-acid tolerant plants, like Lantana.
>>If it were me, I’d let it just remain a forest setting and go fishing instead.<<
You’ve got the only acceptable answer figured out.