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Planting trees from containers
Pot bound (also called root bound) root balls from containers have large or many roots on the outer edge of the ball. They may also have many roots crossing the top of the root ball. It is best not to plant trees in this condition because roots could girdle the trunk as the tree grows. The tree could also become unstable later because few supporting roots grow from the outside curved portion of a root (See: detail about unstable trees).
If you must plant a tree with these root defects, these roots should be cut aggressively with a shovel, knife, saw, or pruning tool to prevent them from girdling the tree later, especially if they are near the top of the root ball. Make three or four slices an inch or two deep from the top of the root ball to the bottom. If in doubt about whether a root is large enough to cut, go ahead and cut it. Tear or peel the outside of the root ball off if you wish. This will be best for the tree in the long run.
Research shows that if there is a shoot growth reduction from root pruning container grown trees at planting, the effect is negligible (Dana and Blessing 1994). Other work shows a reduction in shoot growth following root slicing only if plants are under irrigated (Gilman et al. 1996). Growers report slower growth and some death when irrigation can not be applied appropriately following root pruning.
Recent
studies show that slicing the root ball from top to bottom in several locations
does not increase root growth after
planting (Gilman et al. 1996; 
Dana and Blessing 1994). However, it does appear to enhance distribution of regenerated roots in the backfill
soil profile (see photo below). Instead of growing almost exclusively from the bottom of the root
ball, slicing encouraged root regeneration along the slices from the top to
the bottom of the ball. This could help establish the plant quicker by allowing
the roots toquicklyexplore a larger volume of backfill soil.
Be
sure to remove any synthetic material such as fabric or plastics that might
be wrapped around the root ball (photo above, right). Some of these are designed to reduce root circling
in the nursery but should be removed before installing the tree in the landscape.
Shaving off (lower, right photo) the entire outer edge of the root ball at planting is a recent innovation that shows great promise in helping produce high quality root balls with fewer root defects. If the grower performed the same shaving at each shift to a larger container then shaving the root system at planting as shown rids the tree of most root defects.
