If you want a nice weed-free pile, I would cover with polythene. The turves are moist at this time of year, it will keep moisture in, worms will explore and you will have great loam.
I never go to this trouble and just flip the turves upside down to lie in, and near the top of the hole, a little buried by soil then a thin layer of compost and/or unrotted mulches like straw or wood shavings. It’s quick, weed free and all the turf-goodness goes to the trees.
