September 26, 2015

1 - Proper plant selection, soil preparation, mulch, and irrigation are important for establishing and growing landscape trees in New Mexico.

Yard and Garden September 26, 2015

Q.

I would like to plant an ash tree near the house for shade. I have seen them thriving in parts of town. What steps would I take to ensure the success of such a planting? I have killed a Mexican elder and an Afghan pine in the location where I want to plant the ash. I suspect I overcompensated with water when the trees were young, but it is hard to assign the right amount of water in our climate. I live on the East Mesa on 2 acres of mesquite dunes and salt bushes.

-Thomas H.

Las Cruces

A.

Ash trees can be beautiful shade trees and some species may provide autumn color in some parts of New Mexico. They require more consistent moisture than the Afghan pine and Mexican elder plants that you mentioned. Your area may be fairly challenging for ash trees. Your local NMSU County Extension Service agent can better advise you about the suitability of your area for growing specific tree species.

Another species to consider which is similar but may be better able to grow in your area is the Chinese pistache tree. It is similar in the appearance of its leaves and can tolerate drier soils. Your local Extension Service agent can be very helpful in suggesting a tree to plant.

To grow ash trees or other trees, you may find it helpful to amend the soil over a large area with well-made compost. The goal will be to provide a large area of improved soil to accommodate the large root system of a tree. Tree roots are reported to extend 2 to 4 or more times the height of the tree away from the trunk in all directions. Amending such a large area that would be utilized by the tree at maturity is usually impossible, but the larger the area amended with compost, the better the root system the tree can develop.

Organic mulch applied around the base of the tree and extending outward several feet will also be helpful as the tree becomes established. Organic mulch does not heat as much as inorganic mulch (rocks) and native soil. This protects the roots as they are developing and may also protect the developing crown of the tree.

Finally irrigation, as you mentioned, is an important aspect of establishing and growing landscape trees. Even in sandy soils, daily watering will usually result in problems. In the first growing season the tree may need irrigation twice or perhaps three times each week. Organic mulch will reduce water loss to evaporation and may reduce the frequency of irrigation required. The amount of water to apply with each irrigation is difficult to quantify since soil physical conditions and the presence or absence of organic matter change the required amount of water needed each time you irrigate. However, sufficient water to moisten the soil to a depth of 2 to 3 feet (depending on the species planted) will usually suffice. You can determine the depth to which you have moistened the soil by probing with a metal rod. The metal rod will penetrate naturally compacted soil as deeply as the soil is moist. It will stop when it reaches the dry line, a rock, root, or pipe. Probe in several locations around a tree 12 to 24 hours after watering to determine how deeply the water has penetrated. While the first growing season may require frequent irrigation, in subsequent growing seasons irrigation once every 10 days to 2 weeks will usually be adequate. Organic mulch will again be very helpful. Watch the response of your trees to adjust your irrigation frequency. Wilted leaves in the heat of the day may not indicate insufficient water, but if the leaves remain wilted until morning, irrigation is needed. Browning of leaf edges and leaf tips may indicate that more water has been needed, but this will become apparent much later than the wilting. Browning of leaf tips and edges may also indicate injury by mineral salts in the soil or water. Your local Extension Service agent is a good source of information about this problem.

During the dormant season, trees need less frequent irrigation, but they still need moisture in the soil around their roots. Irrigation once a month is usually adequate during the dormant season. If there has been abundant rainfall or snow, irrigation may be required even less often.

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.

Links:

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

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

Please copy your County Extension Agent and indicate your county of residence when you submit your question!