This practice is still used by tree growers when they want to have a lot of trees ready to go to the market in early Spring. I used to know someone in Canada who used this method every year. He grows 15,000 HP trees every year digs them out in the fall, heels them in and sells them in the Spring to nurseries.

Dig a "V" shaped trench, about 15" deep and 15" wide. Put the tree roots in the bottom of this trench, very close to each other. In other words, you could put about 30 trees in a 10 ft long trench, more if they have small roots. The trees will be leaning 45 degrees. I have no idea why they should be leaning, but I have found references to this practice in several places and the 45 degrees are consistent in every book. Cover the trench with dirt so all the roots are completely covered, water well to remove any air pockets, and leave them alone for the rest of the winter.

You can do this if it is too late to do regular digging and the ground is too hard to work. When the time comes to plant them in early Spring, dig your holes, and transplant your trees. It will be very easy to remove the trees from the trench, since the roots are not attached to anything.