Buying Quality Trees for Planting in Your Landscape
Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist
Before buying a tree to plant in your landscape, make sure it’s a healthy, high-quality plant. Whether you shop for your trees and shrubs at a local nursery or at a discount store, you should keep in mind that the plant is not only an investment of money, but also of time. Don’t waste your time or money on a plant that will not grow well or will become a liability with time.
Some bargains aren’t really a bargain. That’s why the International Society of Arboriculture advises, “When you buy a high quality tree, plant it correctly, and treat it properly, you and your tree will benefit greatly in many ways for many years. When you buy a low quality tree, you and your tree will have many costly problems even if you take great care in planting and maintenance.” The International Society of Arboriculture, or “ISA” for short, is a non-profit organization supporting tree care research and dedicated to the care and preservation of shade and ornamental trees.
So what determines if a tree is high quality or low quality? It’s the condition of the root system, trunk, and framework of branches. A high quality tree is one with an adequate root system for the tree. The container should be large enough to accommodate the roots without circling roots forming on the outside of the root ball. Roots that are circling, kinked, or entwined will continue to grow that way. This usually leads to future problems when the roots eventually choke or “girdle” each other as they grow. A few circling roots can be cut with a sharp knife and loosened, but low quality plants with a tight mass of circling woody roots should be avoided.
If a root ball is dug and wrapped in burlap (balled and burlapped) there should be enough of a root system to support the tree. A rule of thumb used in the nursery industry indicates that the diameter of the root ball should be at least ten to twelve times the diameter of the trunk, as measured six inches above the trunk flare. The “flare” is the area at the base of the tree trunk that curves outward. It’s where the roots meet the trunk. When purchasing a balled and burlapped tree, you should be able to see the flare on the trunk and the top of the root ball should be flat, not mounded and covered with bark.
After you get the tree situated in the planting hole, with the top of the root ball at the same level as it was growing in the nursery, you’ll want to cut all the twine off the ball and carefully pull back the burlap. Remove the burlap by cutting, being careful not to disturb the soil ball surrounding the roots. A plant with many major roots crushed, cut, or torn is poor quality. This will greatly affect the tree’s ability to grow. A plant is also low quality if it lacks enough roots to help hold the root ball together. This type of tree will have severely restricted growth too. However, even a high quality plant may have a few damaged major roots. Use sharp pruning shears to make clean cuts on the injured roots.
A quality tree will also have a trunk free of wounds that are the result of poor pruning cuts or physical injuries to the bark. ISA warns that there are often injuries or problems concealed by trunk wraps. “Never buy a tree without thoroughly checking the trunk.” Problems include poor pruning cuts that leave stubs that won’t “heal.” These can lead to disease and structural defects. Older pruning cuts should show a ring of callus tissue that has covered the area of the cut. These cuts are made just outside what is called the branch collar. If branches are removed with flush cuts, the wound won’t cover over as quickly and can lead to cankers, trunk cracks, or wood decay.
Trees should also have a good, strong basic framework of branches. If the framework hasn’t been well developed in the growing nursery, you won’t be able to correct significant structural defects with pruning. The branches on a tree should be evenly spaced along the central leader. According to the ISA, trees that have branches that are “squeezed” together should be avoided. “Squeezed” branches are where you have two main branches or leaders arising from the same point. As these leaders grow, they “squeeze” each other. The older and larger the tree gets, these leaders often split apart. Squeezed branches can’t easily be corrected by pruning, especially the larger a tree becomes.
You also want branches with strong attachments, ones that aren’t “squeezed” to the trunk. When the angle of attachment between the branch and the trunk is less than 45 degrees, this is considered a weak attachment prone to cracking and breakage. If you’re buying a fairly large specimen, examine the branches and look for small cracks that may already have formed at their bases. A small crack can later develop into a larger one and lead to branch breakage.
Let’s review. When buying a tree... you should look for a one with an adequate, healthy root ball. The trunk should be free of defects and the branches should be well placed along the trunk. Trees can be a significant purchase. Take the time to inspect the tree you’re buying. Inspect the trunk for defects and assess the branch placement and attachment.
Inspecting the root ball is trickier. While I know a horticulturist who recommends removing a tree from its container right in the nursery, most nurseries won’t like you doing this. You certainly can’t look at the roots of a balled and burlapped plant at the nursery without causing all sorts of problems. I recommend checking the roots immediately when you get the plant home. It’s easy to check the roots of a container grown tree or shrub. However, balled and burlapped specimens should first be situated in the planting hole and ready to be planted before removing the burlap.
Some nurseries will recommend leaving the burlap on the root ball. They will not guarantee their plants if you remove the material. However, Mid-Columbia Community Forestry Council members have observed too many problems, such as a lack of roots and severe damage to the root system, beneath the burlap to be comfortable with leaving it on. The burlap also usually doesn’t rot quickly enough in our climate and frequently restricts root and tree growth. The fact that burlap is often treated with copper to keep it from rotting is also a factor in restricting roots. Copper retards root growth. I recommend removing the burlap.