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The Ten Commandments of Tree Planting

By Robert Cox, Colorado State University Cooperative Extension agent, horticulture

Trees evoke all kinds of images. Arbor Day, Earth Day and the coming of spring take care of that.

But, before we dream about their beauty and the cooling shade trees supply through the summer, let's consider The Ten Commandments of tree planting.

Denver's dry climate and generally poor, alkaline soils present some difficulties for trees. Healthy, long-lived urban trees get off to a good start when we pay attention to some tree-planting fundamentals.

Here are guidelines to help ensure that the tree you buy and plant this year will be part of your landscape in the years ahead.

  • LOCATE LOGICALLY - Trees need room to develop root systems underground and branches above ground. Don't plant trees that will grow too large in small areas. Also avoid planting under power or telephone lines or too close to buildings.

Site suitability will determine which, if any trees to plant. The designated site may be in the lawn, near a patio, along a street or sidewalk, in a garden, in sun or in a shaded spot. Soils may be clay, sandy, saline, compacted, wet or dry, gravelly or even full of old building rubble. Whatever the situation, you will need to determine if the site is suitable for growing a healthy tree.

Consider planting for energy conservation. Deciduous trees will shade the west, south and east sides of the home in summer, and evergreen trees along the west and north edges of the lot will provide winter windbreaks.

  • CHOOSE CAREFULLY - For what reasons are you planting the tree? You may want privacy, increased property values, a windbreak, shade, fall color, flowers, fruit or a bird habitat. Perhaps you want to create a sound barrier. Combine this information with knowledge about the site.

This is a good time to visit your local Cooperative Extension agent. You can ask for fact sheets titled "How to plant trees and shrubs;" "Small deciduous trees for privacy and color;" and "Large deciduous trees for street and shade."

You'll want to consider that fast-growing trees often are weak and subject to storm damage. Think about the mature size and shape of trees and learn whether their roots might invade sewer lines, lift and crack sidewalks or make bumpy lawns. Learn which trees are likely to harbor insects or diseases.

  • DIG DILIGENTLY BUT CAUTIOUSLY - Before digging, contact your utility company to mark the location of any underground lines. You could be liable for damage done to such lines.

To prepare the site, mark a circle or square at least 3 times the diameter of the tree's rootball. Excavate the area with a pick and spade. In clay soil, dig to a depth 2-4 inches shallower than the height of the rootball. In sandy soil, dig to a depth equal to the rootball. Leave the bottom of the hole firm and undisturbed.

To the excavated soil, add 25 percent, by volume, of a coarse organic amendment, such as sphagnum peat, compost or aged manure. Mix it well with the excavated soil; this becomes your backfill.

  • PLANT PROPERLY - Try to plant trees when the weather is cool, cloudy and humid, but not windy. If you can't plant right away, keep the tree in a cool, shady, protected spot and keep the roots moist. It helps to soak bare root trees and shrubs in a bucket of water overnight before planting.

Remove any plastic or metal containers from the rootball. Place the tree upright in the center of the planting hole. If the tree is in a fiber pot, tear off the sides. If the roots of a containerized tree are potbound, "tease out" some of the roots and shallowly slit the rootball's sides with your finger or a knife.

For balled and burlapped trees, cut any rope tied around the trunk and pull the burlap away. Cut any reinforcement wire, removing as much as possible, but be sure the rootball stays intact.

Shovel backfill into the hole; continue until roots are covered and most of the backfill is used. Don't tamp the soil with your feet.

  • FERTILIZE FRUGALLY! - Don't put fertilizer into the planting hole; it may cause root injury. Next spring, fertilize young trees lightly.

Root stimulator solutions have negligible value. You can use them, but they aren't necessary for transplant success.

  • WATER WELL - Water the soil at relatively low pressure, using the hose or a "bubbler." Let the water, not your foot, settle the soil. If the soil settles below grade, add more backfill. When done, the planting area should be well-soaked and moist backfill should barely cover the top of the rootball. Watering frequency depends on the soil, not the calendar. Dig with a trowel on the edge of the planting area. Soil that feels moist and holds together when squeezed doesn't need water. Overwatering drives air from the soil, causing root suffocation. Frequent, light watering promotes shallow root development. Mulching will reduce watering frequency.

Send your trees into winter with a good supply of moisture by watering them thoroughly in fall. Water during extended warm, dry periods of winter to prevent drought damage to roots. This is especially important for trees planted the previous year.

  • PRUNE PRUDENTLY - A newly planted tree needs only minimal pruning. Prune out only dead, diseased or injured branches. Research shows that transplanted trees establish quicker when as much foliage as possible remains. If you do prune, don't use pruning compounds on pruning cuts.

  • STAKE SENSIBLY - Trees can be staked too tightly or for too long. Don't stake small trees or those not in the wind's path.

Large evergreen trees, planted in a windy site, will need staking. To stake,do not use garden hose and wire. Instead run wire through grommeted staking straps or use wide strips of carpeting.  This way, the straps, not the wire, passes around the trunk. A year of staking usually is sufficient.

Rigid staking of a tree is counterproductive; research shows trees don't develop normally if they're not allowed any sway.

  • MULCH MEANINGFULLY - A forest tree provides its own mulch with several inches of leaves on the ground. We can imitate this by mulching the planting area with 3 to 4 inches of wood chips, chunk bark, straw, pine needles or shredded leaves. Don't use plastic beneath the mulch; water or air can't penetrate it. Fabric-type weed-barriers are preferable.

One thing you won't see in the forest is manicured lawns around a tree. Research shows that newly planted trees are at a disadvantage when they must compete with grass for water, air and nutrients. Keep grass from the planting area for at least one year. If you mulch around trees, instead of planting grass, you also prevent possible trunk damage by lawn mowers or string trimmers.

  • WRAP IN WINTER - Use crepe paper or other wraps on your deciduous tree trunks about Thanksgiving time; remove the wraps around Easter. Do this for the first 2 to 3 seasons. This protects young trees from winter sunscald. If you've purchased a tree with the trunk wrapped, remove the material now; otherwise the wrap could harbor insects and diseases over the summer.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010