not sure what sort of season you lot are in over in the states, but over here its mid to late spring - not the best time to plant trees but then better than before harsh frosts or immanent scolding sunshine. planting and coppicing is usually always done in the dormant season so as to minimise the damage to the trees whilst they're in sap rise or leaf abscision.
planting a tree to succeed is a tricky business - you need alot of moist weather, and good soil. another common thing over here that causes the death of hardy and delicates is one of the three following...
not staking the tree properly so the rootball is allowed to move around far to much, damaging the absorbing fine root hairs in the process and not letting the specimen establish anchorage roots.
another is to over-nutrient the specimen with compost and mulch causing leaf blemishes, poisoning, perhaps chlorosis or something similar.
its allways good to tickle the root ball before the tree goes in, not too soft or hard - this lets the roots choose thier own route into the soil. another thing is th dig square holes so the roots can congregate in the corners speeding up the anchorage process.
we also have whats called "mychorrizal fungal dip" or something like that which basically lets the symbiotic fungi develop to help the tree to fix its nitrogen. these are sub soil fungi that aren't often seen but sometimes look like tiny ant eggs or something attached to the nodes of the roots. this "root dip" gives the trees all the minerals it needs to stay healthy by encouraging the gowth of these fungi.
hope this is of some help
J
