Watering trees

I planted a variety of young trees and have surrounded them with grass. I am using an impulse sprinkler to water. The hard water seems to damage the leaves of the trees; the smaller trees are really struggling. The grass requires a lot of water. Could I be overwatering the trees, or is the hard water damaging to the leaves? - Barry S. Hobbs, NM

There could be several factors to consider regarding the growth of your trees.

Some grasses use a lot of water and are more efficient at extracting it from the soil than trees. Unless you are watering deeply enough, the tree may not be getting enough water. You should water to moisten the soil to a depth of 3 feet (for new trees at least to the depth of the root ball). This may require irrigating longer (about twice a month). Then, in the intervening time, water deeply enough to keep the grass growing (moisten to a depth of about a foot).

It is possible to overwater. If the soil is staying soggy, you can waterlog the root system of the tree. Water the grass just enough to moisten the soil to a depth of one foot, with deeper watering for the tree as described above. If you are overwatering, the grass should be having problems too.

The various salts in the water (calcium, sodium, etc.) can coat the leaves of the tree and cause some problems. In this case there will be a white, chalky coating on the tree leaves. Using a low-angle sprinkler can help keep the salts off the leaves.

Newly planted trees take a while to establish. They must first develop an extensive root system. While the trees are growing roots, you may not see much growth in the upper portion of the tree.

Trees and grasses are competitive. Some grasses produce allelopathic compounds (chemicals to inhibit the growth of other plants) to slow the growth of trees. It is better to not grow trees and grasses in close proximity to each other for this reason. In time, when the trees have established, they intercept sunlight and the grass ceases to grow. By separating trees from grasses (using mulch material under the trees), you can avoid the chemical warfare that slows tree growth and the later thinning of grasses under the trees.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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