Certified GKH Gardening Expert
I would look for shade tolerant plants and ground covers for growing under trees. The following articles should help: https://www.gardeningknowhow.com/special/xeriscape/xeriscape-shade-plants-plants-for-dry-shade.htm
I've had the same problem..have tried several shade plants but they don't seem to spread at all.... the only thing I've had success with is Forget me Nots which grow prolifically but of course, last only for a short time in the spring. When they finish blooming, I simply mow them with the mower pointed under the tree and they spread quite well....usually the foliage (but not flowers) grow up again before the fall) Each season, I also rake the needles out from under the spruce trees to expose the soil . It seems to help with absorbtion of water...I use the needles to make a path between/around the trees...it looks good and the FmN still grow up through them.