I encountered a similar situation when I planted on the south side of my backyard which was sprayed heavily with Round-Up and had artificial grass. I was afraid that the trees will not thrive or survive at all. I took a chance, tilled the area and drenched it with humic acid (Raw Organic Soil Conditioner- Root Hume- Simple Grow Solutions) from Amazon and hoped for the best. That was in September of this year, my trees have been thriving since planted in the ground mid September or last month in October. Here are some pictures.
After removing artificial grass, soil was compacted rock hard.
After tilling and drenching with soil conditioner.
Added 12" of free mulch from local green waste place and added wood chips on top. Now the trees are thriving and flushing in the winter. I added a PVC structures just in case we get a frost warning, I plan to cover the trees with frost cloth.