October 20, 2012

1 - Silver maple trees often suffer from New Mexico's environment, but proper addition of acidifying agents and iron to the soil can help them look better.

Yard and Garden October 20, 2012


I have a problem with a silver maple tree. In the spring, this tree is the first to leaf out. It is really green and produces quite a bit of new growth. About early to mid-June it starts looking kind of sorry. By mid-July many of the leaves are yellow and turning brown (pictures sent were taken in July). It just keeps getting worse as the summer progresses.

In the fall I apply 16-8-8 fertilizer at the rates recommended on the bag. I also apply 1 pound of ironite ®.

Can you recommend something that I can do to keep this tree looking nice and green through the summer?

Gustavo M.

Deming, NM


Thank you for sending pictures, they help me see exactly what you have described and allow me to make a more confident diagnosis.

Silver maples and box elders are the maple trees most tolerant of maple trees the difficult environmental conditions in New Mexico. Even though they tolerate our conditions somewhat, they suffer from the heat, dry winds, and high pH soils. These conditions result in damage to the leaves during the summer. Even so, they are worthwhile trees to have in the landscape and we can take some measures to help them look better in our difficult environment.

Windbreaks (such as your row of Arizona cypress trees on the windward, west side) help reduce wind burn. Adequate watering and fertilization as you are providing also help. One other thing you can try is to help the tree obtain the iron it needs from the soil.

The high pH of Southwestern soils, due to high levels of calcium and other alkaline minerals, causes the soil to chemically bind iron in the soil so that plants cannot extract it in sufficiently quantities. Your application of an iron product is a good start, but in a phone conversation you mentioned that you apply the iron under the canopy of the tree. A method that may more effectively supply iron to the tree is to apply it beyond the dripline of the tree, where there are more small, absorbing roots to receive the iron.

You can effectively apply the iron product to the tree roots by augering into the soil beyond the ends of the branches. Make holes 2 inches in diameter and 2 feet deep using an auger or by using water from the end of a garden hose to excavate the hole. Fill the hole with a mixture of compost (80%), iron sulfate, or other iron source (10%), and agricultural sulfur (10%). The compost provides bulk so that you will not twist your ankle in holes in the lawn, provides increased water-holding capacity, and as it decomposes it helps acidify the soil around the hole. This acidification helps maintain the iron in a form that is available to the tree roots. The iron sulfate (or ironite ®) acidifies, and provides iron. The sulfur, under the action of soil organisms, forms sulfuric acid, also acidifying the soil and maintaining the availability of the iron.

You can also use an iron chelate product which effectively maintains the availability of iron. Iron chelate with NADDHA as the chelating agent (find this in the ingredients on the bag) is the most effective chelating agent for use in our high pH soils.

You can apply this product at any time of the year, but fall and spring are good times for this treatment. The holes into which you place the iron and compost mixture helps get the water to the tree roots. It is important that you do not make the holes deeper than 2 feet since most absorbing roots for the tree are in the upper levels of the soil. Tree roots will proliferate in the soil near the holes because of increased moisture and the increased water holding by the compost. Increased roots in this area will increase the uptake of iron into the tree. Repeating this process every year or so will increase the zone of good soil and good root growth, which should result in your tree performing better in the challenging New Mexico environment.

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.


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