What does that mean?
Why is it important?
But cant you save a lot of money by buying cheap trees?
What do you look for?
-- health and vigor (at least 4-6" between the old bud scar and the end of the twig)
-- symmetrical general form, with a balance between height and spread
-- freshly dug trees grown for your particular use in a climate similar to yours
-- a single and undamaged central leader (except for certain ornamental trees)
-- well-spaced branches that are evenly distributed around the trunk
-- no branches below 48" from the ground
-- no branches with a narrow angle to the trunk (except for trees like Japanese zelkova)
-- no sign of insects or diseases (egg masses, leaf problems, grubs, etc.)
-- a straight trunk, with no damage except minor scrapes and cuts
-- the caliper size you need (in an urban situation, at least 2" is often specified)
-- no recent pruning wounds
-- no signs of insects (e.g., borer holes) or disease (e.g., sunken areas)
-- a well developed root system, but not a dense mass from being pot-bound
-- no girdling roots--make sure to look, or at least reach your hand down
-- if balled and burlapped, only natural burlap or wire baskets
-- a rootball sized to the height of the tree (see American Standard for Nursery Stock)
"Selecting Trees: A Guide to Purchasing Quality Trees" (1994, American Association of Nurserymen/American Forests), available from your local Cooperative Extension or DEC office, and also from the Community Forestry Education Project at 716-461-1000.