Trees breathe, like we do, but in a different way. Their leaves take in carbon dioxide, water and the sun’s energy, and turn it into sugars that feed the tree. Known as photosynthesis, the process emits vital, life-giving oxygen. Trees’ ability to removal carbon from the atmosphere — and store it in their wood — helps us mitigate the effects of climate chaos: In just one year, a mature tree can absorb half a metric ton of carbon dioxide equivalent. Trees are also essential since they remove air pollutants, prevent erosion, provide shade and wildlife habitat (when native species are grown), and offer many other benefits. And while protection of large, old trees is essential, planting new trees is crucial, and they too must be protected so they can grow to a ripe old age.

If you’ve planted or are considering planting trees in an urban or suburban setting, here are a few things to be aware of that will help your trees grow strong and healthy, including potentially harmful things to avoid:

• The best time to plant trees (and most other plants) is autumn — as they are entering dormancy and as the rains begin. Following leaf drop, however, they are anything but dormant below ground. The Pacific Northwest’s wet, relatively mild winters give them a chance to produce fairly well-developed root systems before the aboveground demands of spring and summer are thrust upon them.

• When deciding which species to plant, choose trees that are locally native to provide the most benefit to wildlife. Also consider light, moisture and soil conditions, as well as topography (since certain species are better at controlling erosion than others). If the area is difficult to water, choose drought tolerant species. Also consider the amount of space you have: Don’t plant too close to property lines (I recommend at least 10 feet from property lines) and check with utility companies if electric lines or gas or water lines are an issue.

• Before planting a sapling, remove any lawn or other plants (especially invasive species) in a circular area, 4 to 8 feet in diameter or out to the drip line (the circular area directly under the outer edges of the tree’s branches), whichever is larger. Dig a hole twice as wide and slightly deeper than the root system; the roots should fit into the hole without being cramped. Rough up the sides and bottom of the hole with a spade or similar tool. Trim off any dead or damaged roots and branches with clean pruning shears. For bare-rooted trees, mound a cone of soil at the base of the hole and drape the roots over it, gently untangling roots if necessary. For potted trees, massage the root ball to loosen and unfurl roots that are tightly wound; otherwise they may be difficult to establish. Note: when transporting non-bare-root trees, always support the heavy root mass from below; never lift or carry them by their stems.

• Place a straight stick across the top of the hole to help judge the depth at which to plant. Since the number one cause of tree mortality is planting too deep, be sure to place it slightly above the level grown at the nursery. Straighten the tree, judging its posture from several angles. Replace the original, native soil around the roots until the hole is filled halfway, lightly firming to avoid large air pockets, then water. Once it’s drained, adjust the depth of the tree if necessary, and backfill with more soil, firmly tamping it down to prevent air pockets. Water again thoroughly. Apply about 3 inches of organic mulch to the area, keeping it at least 6 inches away from the trunk, but slightly thicker on the outer edge to prevent erosion. Don’t use fine bark mulch or gravel or rocks.

• When saplings are planted, they’re often staked, regardless of whether or not they need it. Staking is actually only helpful if they are planted in very windy areas, if they are bare-rooted, or if they have little root mass. Plants need to experience movement — just as we do — to become strong and healthy, and improper staking can cause irreversible damage. Staked trees often have weaker trunks and less developed root systems than trees that are not staked. To test whether or not a newly planted tree needs staking, grab its trunk and move it back and forth after planting; if movement causes shifting soil, stakes will stabilize it. If necessary, small trees can be supported with two 5- to 6-foot-long stakes (on either side) driven 1 to 2 feet deep (depending on soil conditions) outside the root zone. To stake a very large tree, space two to four stakes equally around the hole, placed several inches away from the root ball of a containerized plant and 2-3 feet from the trunk of bare-root trees, preferably before planting—if afterwards, stakes should be placed just outside the planting hole to prevent damage to roots. The stakes and ties should be situated perpendicular to the prevailing wind when space allows. After planting, tie the trunk loosely to the stakes, about 3 feet from the ground, with a soft tie (never use wire) in a figure-eight loop, so that the tree is not completely immobilized and can move a bit with the wind. Very small trees can be loosely tied to a single stake. Check ties periodically to be sure they’re not too tight or causing abrasion. Remove ties as soon as the tree is stable in the ground, usually within about one year.

• Immediately after planting a tree, always remove any sticks or rods that are taped to the trunk, since failing to remove them can lead to girdling, as shown in this photo. They are only meant to prevent damage to the trunk during transport; they are not meant to be taped on indefinitely.

Tree irrigation (“gator”) bags have limited benefit and often cause more problems than they’re worth! On my winter walks I often see young trees with their lower trunks covered in such plastic, and I unzip them whenever possible to allow air to reach the damp bark.

The problem is this: Eventually, the plastic (or almost anything that covers a tree trunk) will lead to a moist, dark, low oxygen environment that damages the bark and allows pathogens to invade. These bags are not meant to be left on year round, especially during the rainy season, so please remove any that you have, inform neighbors, or unzip those that you see (guerrilla unzipping, anyone?) In addition, these bags are only meant to be used for about one year, since following that period a tree’s root spread will generally be directly below the drip line (the circular area located directly under the outer circumference of a tree’s branches). Most water absorption occurs by feeder roots at the drip line (or in some species, such as oaks, quite far beyond it), so watering close to the trunk does no good (the vast majority of trees do not have tap roots) and can even cause roots to grow in a circular or spiral pattern around the trunk at or beneath the soil line, which can lead to a gradual girdling or strangling the trunk. What’s the alternative? Old-fashioned watering with a hose or watering can. Researchers who looked into artificial watering devices found no evidence that watering devices benefit tree growth and health, compared to direct watering. One possible advantage of using watering devices is less surface runoff due to their slow release, but the hazards of using bags more than a year or two (at most) is not worth the risks. Bags have to be filled with a hose or watering can, so why not just use those? Doughnut-shaped devices (or “ring bags”) don’t keep bark as moist (although they can keep the base of the trunk wet), but like gator bags, they also only apply water at the base of a tree’s trunk, so should definitely not be used for more than a year or so. Here are some good tips on watering trees from OSU.

© 2025 Eileen M. Stark