June 5, 2010

1 - Plants can be sun burned, but you can help avoid the problem.

Yard and Garden - June 5, 2010


I took my plants outside for the summer as I had always done in my home in Tennessee before I moved to New Mexico. Within a day the leaves on many of the plants turned white and then brown. I think I may have killed my houseplants! I know New Mexico is a lot drier than Tennessee, but I watered them well and they died so fast I think there must be another problem.


The sunlight is much more intense here in the arid Southwestern U.S. We are at high elevation and there is little moisture in the air to reduce the intensity of our light. You sunburned your plants. Some plants, especially woody plants, may be able to recover and produce new leaves. Some herbaceous (non-woody) plants may die, and others may sprout from the stems or the base. Be patient to see which can recover.

Move your plants to a shady location. Morning sun is good, but by late morning the light intensity becomes too great for many houseplants. Some trees, like mulberries and catalpa trees, cast too dense a shade for many houseplants, but for others it is perfect. Honeylocust trees cast a lighter shade that is good for houseplants that need more light. Other trees also make good shade. Some houseplants will do well in the shade on the north side of your house; others will do better on the east side. Move your plants from site to site until you find the right place. Your plants will tell you when you are there by producing healthy growth without sun burning. However, move them slowly from shadier to brighter locations, giving them time to adjust as you move them. Remember where you put them so you can put them in the same location next summer.

Plants have the ability to adapt to different light levels within limits. They produce sun leaves when grown in bright light and "shade leaves" in the shade. In the shade the leaves are more efficient to utilize the lower levels of light, but in the brighter locations the leaves adapt by increasing protection against the higher light levels, but become less efficient. Lowered efficiency does not cause problems until you take the plants indoors for the winter, then the sun leaves will often fall off and be replaced by shade leaves under the dimmer light conditions indoors.

Vegetable and flower transplants from the nursery often go through this adaptation process as well. Plants grown in humid greenhouses will often have shade leaves and should be gradually adapted to the outdoor conditions. In the garden they must adapt to increased light, drier air, wind, and sometimes to higher or lower temperatures. Plants are able to adapt, but they should gradually be acclimated to the new conditions. To do this put them in a shady, protected location when you first take them home, then gradually move them to brighter, drier, less protected locations before planting them in the garden. Or, you can build protection around the plants immediately after planting them in the garden. Cover them with old brush from shrub trimming, or place some other material on the upwind, sunny side of the plants until they can adapt. Transplanting will be less shocking to the plants if they are given time to adapt to the harsh garden 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.


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

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