Water when you can. I put a bucket outside and let it fill with rain. IF the bucket is empty for 3 days, I water. After mid august I water less often if at all. I helped the tree survive the first bulk of the summer.
I dig deep when I plant my trees. I ammend with peat moss and some lighter potting soil for my heavy clay soil at home. At camp, its sandy soil. I bring clay soil from home and heavier raised bed soil from the sotre. Mulch plenty too. Atleast a bag per tree. I also collect leaf mulch and concentrate it around the tree.
I water about 7-8 gallons a tree. I have 5 gallon water jugs with a 14" hole drilled in the bottom. They take about 10 minutes to drain out Might be a touch too fast, but I think the water goes deeper this way. The other half of the water I spray around the drip line. I spread around 2 gallons, then fill the bucket, the spray another gallon or two around the drip line, then top off the slow drip bucket.
I also put a small dam of soil around the tree, maybe a 2-3ft diameter circle. You can flood the spot without it running off too far.
Trees at camp get watered if they need them when I am there. They've been doing ok. No dead ones. All anty roots.
Another good thing to do is take a metal rod and push holes in the soil deeper. Fedco trees suggested it, I have tried it at my house.
Another thing you can do is plant the tree is some shade. If you got some shrubs or trees you need to clear at an edge of a field, leave it up there for a year while theapple treesgets some roots. You can also use a tree cage and put something on the top of it to shade it a bit too. I do that with freshly grafted trees. Also, keep birds away too.