Southern magnolia in New Mexico

I bought 2 Southern magnolia trees when my house was built last year. They were planted by a professional from the nursery where I purchased them. Why are the leaves brown like they are dying? The trees look good, just the leaves seem to be dying. Some leaves are green and others are green and brown? How often should they be watered?

Irene P.

Alamogordo, NM

The Southern magnolia is a broadleaf evergreen tree native to the Southeastern U.S. That region of the U.S. has acid soils and, more importantly, humid air. The Southern Magnolia is not well adapted to our dry air and shows this as their leaves turn brown. It will often survive in New Mexico but will have many brown leaves. Magnolias on the north side of a house often look pretty good until they get larger than the house, and then winds blowing over the roof begin drying the leaves.

To minimize this browning of the leaves, the magnolia does best in an area protected from wind and direct afternoon sunlight. A structure (house, garage, etc.) is useful for a while. A windbreak of taller trees is better than a house, especially when there are trees to the west to provide afternoon shade.

Watering will depend on the type of soil in which the trees are growing. Sandy soils should be watered a little more frequently with less water while clay soils require greater quantities of water, which should be applied much more slowly and less often. Loam soils are intermediate. A general guideline that you can modify slightly (depending on your soil conditions) is to irrigate newly planted trees once a week the first one or two growing seasons. Then, in subsequent growing seasons, reduce the irrigation frequency to once every two weeks. During the dormant season, water once every month. Even though the tree keeps its leaves, it uses less water during the dormant season. In all cases, change the frequency of irrigation but not the quantity of water applied. When you water, apply enough water to moisten the soil to a depth of three feet (if the soil is that deep in your location). In areas with a shallow caliche or rock layer, large raised beds may allow growing small trees; however, the Southern magnolia is not small and may not tolerate these conditions. The amount of water to moisten to that depth depends on the soil type and is best determined by trial and error. Your County Extension Service agent can help you make this determination.

Even with proper watering, the tree may suffer for a couple of years until the root system recovers from the transplant shock. However, because of our alkaline soil and dry winds, the magnolia will rarely look as good in New Mexico as those growing in the Southeastern U.S.

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.

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