June 15, 2013

1 - White, water-based paint on the trunks of thin-barked trees may help them survive the winter.

Yard and Garden June 15, 2013


I need to paint some of the trunks on my ash trees as they are getting sun injury. Please tell me what kind and color I should use.

Gloria H.

Rio Rancho


Painting the trunk of a tree is an effective way to reduce heat and sun injury to the trunk. The object is to reflect sunlight to prevent heating of the bark. Trees with thin bark, young trees or trees that never develop a thick bark are those that benefit most. White paint is best for reducing injury to the trunk. Darker colors will absorb sunlight and convert it into heat that can cause even greater damage to the trunk. The paint should also be water-based, not petroleum-based, to prevent the paint from causing injury.

The injury to the trunk occurs most often in the winter when the trunk warms during the day and freezes at night. The southwest-facing portion of the trunk warms most and is most often injured. Most gardeners will paint completely around the trunk rather than just the southwest side of the tree for aesthetic reasons. They do this in the late fall. It is OK to paint the trunk of a very young tree in the summer if the branches and leaves do not provide sufficient shade to protect the trunk. However, it is more important to paint the trunk of young trees with unshaded trunks during the late fall.

Another gardening practice that helps avoid trunk injury is proper irrigation, especially in the winter. By proper irrigation I mean that the water is supplied to soil where the absorbing roots are located. In very new trees, that is the region of soil in which the original rootball is located. Older trees should not be watered at the base of the trunk; rather the soil at the drip line of the tree and outward should be targeted during irrigation. The soils should be moistened to a depth of 2 to 3 feet every 10 to 14 days in the growing season, and once a month during the dormant season. Maintaining moisture in the tissues of the trunk will help moderate temperatures.

Use of organic mulch around the base of the tree or living plant material around the tree helps reduce heat stresses experienced by the trunk. Rock mulch heats up the surrounding environment more than bark mulch. If the landscape has significant areas of rock mulch, use bark mulch at the base of trees to protect them from summer and winter heating. Rock mulches can increase winter damage to tree trunks.

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.

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

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