By: Steve Piskor
©2015 Penn State Master Gardener & Pennsylvania-certified horticulturist
Trees form the backbone of a garden. They are the most prominent, costly and permanent plants in a landscape design. Most trees live for decades. With these factors in mind, special care must be taken when selecting, planting and maintaining a tree during its lifetime.
In this article I will focus on selecting the perfect tree for your garden. Before going tree shopping, you must answer some fundamental questions:
1. What function will the tree serve?
Do you desire shade or a windbreak? What ornamental qualities would you like? Trees can be grown for their foliage, flowers, form, bark and color. Are edible fruits or support for wildlife a consideration?
2. Where will the tree be sited?
Consider the location’s exposure (sun to shade) and soil quality (depth, drainage, moisture). Determine if it will be subject to windy conditions or road salt.
3. How large will the tree get?
It should be placed where it can grow to its mature height and width without interfering with other plants, utility lines or structures. It is pure folly to plan to keep a tree at a desired size via pruning. From a design standpoint, it should be in proportion to the other objects in the landscape.
4. Evergreen or deciduous?
If you want foliage throughout the year, an evergreen (broadleaf or needle) is the obvious choice. If seasonal changes (including leaf drop in the fall) are a priority, consider planting a deciduous tree.
5. How much will it cost?
Depending on the size, availability and rarity of a tree, it can cost thousands of dollars. You will save substantially if you’re willing to start with a smaller tree and can plant it yourself. If you desire instant impact, be prepared to pay more for the years of care a tree requires to grow into a large size.
Using the above criteria, search the Internet, catalogs and books to narrow the choices to several candidates. Visit a local nursery and speak with an experienced grower about your selections and ask for suggestions. Observe mature trees in your area and be realistic about their ultimate size.
Now that you’ve decided on the “perfect” tree, it’s time to go shopping. A nursery is the best place for evaluating a tree. Growers have trees of various sizes in their fields, and you can often choose the exact specimen for your garden. Nurseries and landscapers can also source trees from other growers. You can rely on their expertise to select a fine tree.
If you’re looking for an unusual one that can’t be found via a nursery, online sources are an option. Trees ordered online are shipped bare-root and typically dormant. They will be small but usually do very well once planted in the garden.
At the nursery, evaluate the most important parts of a tree — its roots and shoots:
The root system is too often overlooked when evaluating a tree. An unhealthy root system will cause a tree to struggle and probably die. The roots are packaged using several different methods — bare-root, balled-and-burlapped (B&B) and container-grown.
• Bare-root trees have all the soil removed, making the tree easier to transport and reducing costs. This type of root system is susceptible to drying. Watering, handling and planting a bare-root tree requires special care.
• Balled-and-burlapped (B&B) trees are dug from a nursery bed. The roots are wrapped in burlap (natural or synthetic), then encased in a metal basket to secure the root system. The major disadvantage is that a majority of the tree’s roots (greater than 90 percent) are left in the field. To maximize survival of a B&B tree, verify that the diameter of the root ball is at least 10 times the diameter (caliper) of the tree trunk, measured 12 inches above ground level.
For example, a tree with a 1-inch caliper should have a root ball that is 10 inches or more in diameter. If there is a choice between several sizes of the same tree (genus/species), select the smaller size. Besides cost, studies have shown that a smaller tree adjusts to its new home more quickly, and over time, can catch up with and surpass its larger counterpart.
• Container-grown trees are grown directly in a container. Their entire root system is contained within the pot. If possible, carefully remove the tree from the container and inspect the root system. The roots should hold the soil mass together and be evident on the outside of the soil ball. A root ball that is tightly encircled, dense and is growing through the holes in the container has been in the pot too long, and it may not be a good candidate for the landscape.
For B&B and container grown trees, it is important to inspect the lowest part of the trunk at soil level. The trunk should become wider as it enters the soil. This area is called the root flare. The root flare must always be visible above the soil level. If it isn’t, the tree is likely planted too deeply, which can lead to problems in the future.
Once you’ve determined that the root system is healthy, look at the parts of the tree above soil level, the shoots.
• The trunk should have a good taper from bottom to top.
• The leader (or leaders) should be strong and well-developed. Many trees have single leaders. If it has a second or co-dominant leader, it can cause future problems with the shape and growth of the tree.
• Lateral branches should be well-developed and spaced around the tree’s trunk. They should have a considerably smaller diameter than the trunk. Good spacing between branches is in the 8- to 12-inch range.
• The angle between the trunk and a branch (called the crotch angle) should be wide. A branch attached via a narrow crotch angle is weak and can easily break in a storm.
• There should be no signs of insects, disease or other damage on the leaves or woody parts of the tree.