Discover guidelines for determining tree quality at time of purchase and for identifying problems with tree structure, roots, and injuries.
A high-quality tree, when planted and cared for correctly, may become a long-lasting asset to your property. In contrast, a low-quality tree may develop costly problems over time, increasing the need for maintenance and reducing the benefits a tree can provide.
What Determines Tree Quality?
A high-quality tree has:
- strong form with well-spaced, firmly attached branches
- a trunk free of wounds or damage
- a quality root system to support healthy growth
A low-quality tree has:
- weak form in which multiple stems originate from the same point and branches grow into each other
- a trunk with wounds from handling or incorrect pruning
- limited, crushed, or circling roots in an undersized root ball or container
These problems, alone or in combination with each other, can greatly reduce the tree’s prospects for a long, attractive, healthy, and productive life. When buying a tree, inspect it carefully to identify problems related to form, injuries, or roots (remember the acronym FIR).
When buying a young shade tree, it is important to note that the branches you see may not be present at maturity. Many lower branches will be shaded out as the tree grows, or pruned away to allow clearance for pedestrians, traffic, mowing, or other activities.
Young trees often have few naturally occurring branches. Branching increases as a tree ages. As a result, many nurseries prune young trees to spur crown growth. While giving a tree a fuller appearance, this practice may lead to issues that must be addressed later with corrective pruning measures.
Good, strong form – or architecture – starts with branches evenly spaced along the trunk. The branches should have firm, sturdy attachments with the trunk. Very upright branches with narrow angles of attachment may cause problems later on as they grow into the trunk. Branches that press against the trunk or each other signal problems. Areas of contact may become compressed, may crack, or die back. When several branches are growing at the same position on the trunk, the likelihood of weak attachments, compression, and cracks increases greatly.
If you desire a tree with multiple trunks, make certain that the trunks are well separated at the ground line. Remember, trunks expand in diameter as they grow. Two trunks may be slightly separated when small, but as they grow in girth, the trunks will squeeze together.
Many architectural issues can be addressed through corrective pruning or training. Begin corrective pruning one year after planting. Space the pruning over several years.
Remove only broken or torn branches at the time of planting to allow the tree to recover from the stress of transplanting. After a year, start corrective pruning by removing any branches that died after planting.
Never buy a tree without thoroughly checking the trunk. If the tree is wrapped, remove the wrap and inspect the trunk for wounds, incorrect pruning cuts, and insect injuries. Wrap can be used to protect the trunk during transit, but should be removed after planting.
Incorrect pruning cuts on the main trunk are major problems. Cuts that remove or injure the swollen collar at the base of branches may lead to problems, such as canker formation, decay, and cracking. Incorrect pruning practices that leave a stub prevent a tree from recovering from the cut. Incorrect pruning cut: branch collar injury.
A correct pruning cut removes the branch just outside of the collar. A ring, or “doughnut,” of sound tissues then grows around the cut. Do not make cuts flush to the trunk. The closing tissues may form only to the sides of the flush cuts. Trunk tissues above and below flush cut branches often die. When high summer or low winter temperatures occur, cracks or long, dead streaks may develop above and below the dead spots.
Nursery trees are often classified based on how they are produced, harvested, and sold. Each type of tree has a unique root system:
- bare root: no soil surrounding roots; usually on small trees.
- balled and burlapped: roots of field-grown trees surrounded by soil and held together with burlap and wire or rope.
- container: roots and soil in a container.
Bare Root Stock
Bare roots should not be crushed, torn, desiccated, or discoloured. The ends of the roots should be cleanly cut. Damaged roots may be cut cleanly prior to planting and watering.
Balled and Burlapped Stock
You should be able to see the trunk flare (the area where the trunk widens and connects with the roots) at the top of the root ball. Avoid buying plants with badly damaged or compressed root balls. The top of the root ball should be flat. Rounding may be an indication of major woody root loss.
The diameter of the root ball should be at least 10 to 12 times the diameter of the trunk as measured 15 cm above the trunk flare.
Roots should not twist or circle in the container. Remove the root ball from the container for inspection, paying special attention to larger, exposed roots. Circling roots may girdle and kill other roots or the entire tree if wrapped around the lower trunk.
Fine circling roots may be cut away at planting. Larger roots may be straightened if still flexible. As with balled and burlapped stock, you should be able to see the basal trunk flare with container-grown plants. If the trunk flare has been buried, gently expose it before planting the tree, taking care not to damage the bark