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Watering Trees and Shrubs

Excessively dry soils kill small roots and reduce a tree’s capacity to absorb water, even after the soil is re-moistened. The resulting drought stress increases a tree’s susceptibility to certain diseases and insects. Precious energy reserves must be used to replace the lost roots. Keep your trees and shrubs adequately watered by following the guidelines listed below.

Checking Soil Moisture

There is no way to look at the soil from above and tell how much moisture is in it. The only way to be sure of how much moisture is in the soil is to probe or dig. A trowel, metal rod, or soil sampling tool can be used. Low-cost soil moisture meters are not very accurate. A metal rod, such as the end of a root feeder (without the water running), may be the most convenient tool for the homeowner to obtain and use. Very dry soil will resist penetration of the rod and indicate the need for watering. After a little bit of practice, anyone can learn to use this simple tool.

Newly Planted Trees

Proper watering is the single most important maintenance factor in the care of transplanted trees. Too much or too little water can result in tree injury. Newly planted trees and shrubs may need to be watered regularly for two to three years until their root systems become established. Large trees may take longer. For the first few months of the growing season after a tree is planted, the tree draws most of its moisture from the root ball. The root ball can dry out in only a day or two, while the surrounding soil remains moist. To water the root ball and surrounding area, let the hose run slowly at the base of the tree or use a root-watering needle under low pressure for 5 to 10 minutes.

Established Trees

The top 8 to 12 inches of soil should be kept moist around trees during periods of drought, at least as far as the branches spread (dripline). It is impossible to give a formula on how much or how often to water a tree to keep the soil moist 8 to12 inches deep. The amount of water required will vary with local site conditions, but without adequate rainfall, established trees may need to be watered as often as every 10 to 14 days. Don’t wait until your plants show signs of stress, such as wilting or yellowing. Any of several methods of watering work well as long as you are focusing the water at the roots.

If the ground is level, simply let an open hose run on the ground and move it around occasionally to get good distribution. If the ground slopes a little, water may easily run off the surface, and a sprinkler or soaker hose would distribute the water more slowly.

If the ground slopes severely, a root-watering needle may be necessary. Insert the needle no more than 6 inches into the ground, and move it around frequently since it moistens a small area around the insertion point.

No matter which watering method is chosen, it is important that you don’t saturate the trunk and that you keep the top 8 to12 inches of soil evenly moist throughout dry periods.

Helpful tips for successful tree planting.

A Wide Hole, Not Too Deep

A tree needs a wide, shallow hole so it can spread out new roots. Trees that are balled and burlapped lose between 70 and 90 percent of their root mass when they are dug up for transplanting.

Ways to Buy Trees

Trees from nurseries come one of three ways: bare-root, balled and burlapped (B&B), or potted (containerized).

• Bare-root trees have exposed roots without any soil on them. The roots must be kept moist and covered because they can dry out quickly. Bare-root trees are usually small—less than 2-inch caliper— and should be planted when dormant (late fall or early spring). Bare root trees are uncommon in northern Illinois.
• Balled and burlapped trees are dug up with some roots in a ball of soil that is then wrapped in burlap. The soil helps keep the roots moist.
• Potted trees are becoming widely available. They can become rootbound, so remove the pot and carefully unwrap or even cut back circling roots when planting.

Mulch is an important part of tree care.

Mulch helps keep tree roots cool in the summer and holds moisture in the soil. It keeps lawn mowers and string trimmers safely away so they do not damage the tree’s bark. Mulch also deters weeds and improves the soil as it breaks down.

Mulch should be made of plant material that will decompose over time. The best material is chipped or shredded wood, although leaves and grass clippings can be used. Do not use gravel or stone.

Spread mulch in a wide saucer shape around the tree’s trunk. Mulching imitates the way trees grow in nature. In the wild, the forest floor is covered with a layer of twigs, decomposing leaves, branches, and other dead plant matter. In urban areas, trees do not have this natural mulch layer and often have to compete with turfgrass for nutrients and water. Even in mature trees, most roots are just below the soil surface. Typically, 90 percent of roots are no deeper than 18 inches.

Replacing grass with mulch protects trees and helps them grow. Maintaining a mulch layer over a tree’s root zone is one of the most important and effective ways to help trees live long, healthy lives. However, piling mulch (or soil) against the tree promotes trunk encircling root development and can shorten the life of the tree. The goal is to mulch the soil, not the tree!