According to Robert Kourik in his book Roots Demystified, air pruning is the next best thing to seeding in place (for which there is no substitute). The research comes from the logging industry seeking the most effective and efficient way to replant deforested areas. The best method, according to Kourik (and based on methods established in the 1980s) is a tube with ribbed edges to direct roots down and prevent root circling, including some holes at the base for air pruning. The best tube will also allow for easy removal of the tree seedling. Kourik's book is from 2008, and he complains that finding tube-grown seedlings is difficult. The next best approach, he suggests, is small seedlings in pots--the smaller, the better. Other sources have suggested that anything over 1 year old grown in a pot will be root bound. Moreover, staking is generally a bad idea; better to use nurse shrubs as windbreaks. The wind helps trees root in a healthy manner. If staking is required, best to use one stake on the windy side, screw in an eye screw to the sapling with one string tied to the stake.
