Tree irrigation in winter and fall

I planted Arizona cypress and Lanceleaf cottonwood trees last spring and have been watering deeply twice a week. How often should they be watered through the winter? Also, I am now (fall) planting another Lanceleaf cottonwood. What water regimen should be used?

Chris
Santa Fe

The trees planted last spring should have developed a reasonable number of roots this summer and fall, so they may be watered once a month throughout the winter. If they are planted in sandy soil and there is a good layer of mulch over the roots, once a month will be sufficient. If the soil is clay, it will hold more water, but once a month should also be adequate. As you water now and in the winter, remember to irrigate the soil to the same depth as in the summer. When you reduce watering, reduce the frequency but not the quantity of water applied with each irrigation so the soil is moistened to the same depth.

Fall is a good time to plant trees, but the newly planted trees should initially be watered a little more often in sandy soil. Irrigate to the depth of the rootball once every two weeks until December, and then reduce irrigation to once a month until spring when the leaves begin to develop. Once leaves have developed, gradually increase irrigation frequency. (Remember to apply the same quantity of water with each irrigation.) By the time the temperatures begin to reach 80 degrees or more on a regular basis, you should be watering twice a month.

The reason you can water less often in the winter is because the water in the soil evaporates less rapidly during the winter, and the trees (especially the deciduous trees) use less water. An evergreen tree (your Arizona cypress) still has leaves and needs water, but even it uses less water in the winter. Mulch will help maintain more constant soil temperatures and soil moisture. It will greatly benefit your trees.

Selecting a colorful Chinese pistache tree

I saw a very beautiful Chinese pistache tree but have noticed that other Chinese pistache trees are not as pretty as the one I saw this autumn. I want one, but I want to be certain that the one I plant will have good fall color. How do I get one with good color?

The best way to increase your chances of having good fall color in any plant is to purchase it in the autumn when you can see the color. Many plants do not look as good in a container as they will once planted in the landscape, but the potential fall color should be evident. Soil conditions and irrigation may also have an effect on color, but by choosing the plant in the fall you greatly increase your chances of having the fall color you desire.

Fall is also a good time for planting many trees and shrubs. For most of them, root growth occurs in the fall after the air has cooled and the leaves have fallen. The temperatures below the soil surface remain suitable for root growth for quite a while after treetops have become dormant.

Fall is a good time to plant your tree, and you can select your fall color. In northern New Mexico the time is drawing short, but from Central New Mexico (lower elevations) and southward there is still time.

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.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

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