Yes, a picture would help.

Two reasons for failure of new plantings are insufficient or excess water.

And never improve the hole you will plant in (especially important for trees.) Just improve the soil. Peat is never a good choice; once it dries out, it is nearly impossible to wet again.

Was the grass large and very pot bound when you planted it? I have found this to be a problem and I've lost more than my share by planting large "instant gratification grasses" because the root ball is so dense it won't root into the surrounding soil and I scratched up and cut though the dense roots prior to planting like they tell you to do. They seem to start dying almost right off the bat after planting and keep declining. When I dig up the dead grass, that rootball looks just like when I planted it, still in that pot shape. I do better buying smaller 4" pots which quickly establish and grow into a gallon size plants.

Several years ago when I had a more conventional landscape I bought many, many bags of peat & endless bags of play sand and mixed them into my beds well and deep. Over the years I also dug in grass clippings and leaves. I never had any problems with adding peat. Peat only creates that 'difficult to wet problem' that when its mostly peat, like in a pot.