Trees are a site’s biggest asset. These guidelines will help you protect and manage them through a construction project and beyond.
ASIDE FROM ADDING beauty to landscapes, trees perform several vital functions. They help stabilize soils, absorb rainwater and reduce the velocity and volume of rainwater hitting concrete and other impervious surfaces. They provide shade, especially on south and west façades; in the dry climate of the Southwest, for example, a shade tree can lower temperatures by up to 20 degrees. Trees also block wind, especially when planted near north façades. And they capture and store carbon.
The USDA has developed a software tool called iTree that can help a city quantify the benefits of its trees. www.itreetools.org
“Planting trees is as important as not spewing carbon dioxide into the atmosphere,” says Dave Barmon, owner of Fiddlehead LLC, a landscaping company in Portland, Oregon. He has seen a trend away from planting trees that grow large, mostly because of their maintenance (including the large volume of fall leaves) and concerns that the tree will cast too much shade. Barmon points out that pruning can train a tree’s canopy to the desired shape and size, and even maximize its potential for usable lumber at the end of its life.
“Pruning for good lumber remedies a lot of other problems,” he says. A straight tree with one strong leader and subordinate branches is healthier than one with large crotches that encourage water to pool, or one with multiple leaders (or worse, one that has been topped). Regular pruning is essential for keeping trees healthy and remedying damage from wind, storms and disease. Barmon recommends hiring a pro for large trees. If you tackle a limbing or pruning job yourself, be sure to wear protective clothing (gloves and chaps), don ear and eye protection and follow best practices for operating a chainsaw.
When choosing new trees, native species are always a good choice, since they’re adapted to the climate. (Some cities keep a list of preferred “street trees,” so be sure to consult the planning department before planting trees near sidewalks and streets.) Fruit trees have the added benefit of producing food, but require more maintenance. Make sure to choose varieties that are a good match for both the region and the site conditions. “For example, peaches are a terrible choice for Portland,” says Barmon. “Persimmons, cherries or native pawpaw are a much better option.”
As with all landscaping decisions, consult an expert when in doubt, and take the time to do your research before planting a new tree. Hopefully, it will live to benefit several generations.
From Seedling to Shade Tree
The Arbor Day Foundation created an online guide for choosing and caring for trees. We have adapted it here, so you can help your clients make good choices that will benefit them now and for decades to come.
Right tree, right place. When purchasing a small tree, think ahead to when that tree matures. Will it block windows or grow into utility lines? Consider the tree’s hardiness zone, sun exposure and the soil conditions of the site. In general, plant deciduous trees on the south, southwest and west sides of a building. That way, they will shade during the summer but allow sunlight though in winter. Plant conifers (evergreens) on the north side of buildings, where they can block wind.
Choose a healthy tree. Whether bare root, ball-and-burlap or potted, look for healthy bark, good branch spacing and abundant root growth. Avoid rootbound trees—that is, roots that circle around the inside of the pot. If it’s a more mature tree, look for a strong leader and good branch spacing. Low branches help develop a tapering trunk.
Bare-root trees: Soak in water for several hours, and make sure roots are covered right up until planting.
Rules of Thumb for Pruning
- Never remove more than 1/4 of the crown in any one season.
- Main side branches should be 1/3 the thickness of the main trunk.
- Don’t prune up from the bottom more than 1/3 of the tree’s total height.
- Prune side branches to encourage angles of “10 o’clock” and “2 o’clock.”
- When shortening side branches, cut at an angle just above a lateral bud.
- Make sure tools are sharp.
Image credit: International Society of Arboriculture; bugwood.com
Containerized trees: Remove the tree gently, without pulling the trunk away from the roots. If rootbound, cut four vertical slits up the sides and an “X” on the bottom.
Give it a good start. Dig a hole wider than necessary. Remove grass, if present, and till soil to encourage roots to spread. Adding amendments could keep the roots from growing beyond the amended area, so stick with native soil. Plant the tree so that the root collar—the bulge just above the root zone—lies at or just above ground level. Pack soil around the tree and create a basin that will hold water. Water newly planted trees well.
Mulch it. Mulching insulates the soil and helps it retain water; it also helps prevent roots from compacting and keeps weed growth in check. Remove all grass from between three and 10 feet from the center, depending on the size of the tree. Mulch with two to four inches of wood chips. Do not allow the mulch to come into contact with the tree trunk.
Water well. Trees should be “watered in” immediately after planting, and should be watered regularly for the first two years afterward. That said, overwatering is a common mistake, so do the “trowel test” by sticking a spade two inches into the soil and creating a small trench. If the soil is moist to the touch, you don’t need to water.
Pruning. Pruning is most often done in the winter, while the tree is dormant. Don’t prune in the fall, when decay fungi spores are active. To enhance flowering, prune summer-blooming plants in winter or early spring; prune spring bloomers right after the flowers fade.
Tree Protection. A construction project can be hard on trees. Many municipalities require tree protection fencing throughout the project’s duration. Even if it’s not required, safeguard trees by keeping materials and heavy equipment out of the dripline, and keep excavated topsoil away from the trunk. If a tree must be sacrificed for the project, consider transplanting it, or if it’s a large tree, having it milled for usable lumber.