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Issue: October 30, 2010

The first frost may not kill all garden plants

Q. I think I had a little frost in my garden last week. I saw a little white coating on my lawn. Leaves on some of my plants turned black, other plants show no signs of injury. Why were only some plants killed by the frost?

A. There are a couple of possible answers to your question. First is that some plants are hardier than others. Squash and pumpkins will show injury (blackened leaves) at temperatures and cold durations that do not injure tomatoes and chiles, even though these are also warm season crops. Corn and beans may also show little damage. Tomatoes may show injury before other plants. Cold season crops such as cabbage, broccoli, Brussels sprouts, carrots, and other plants that like the cold will tolerate even more cold. So, perhaps the temperature (and duration) was just enough to damage some plants and not others. Another possibility is that the temperatures were warmer in parts of your garden. Cold air is heavier than warm air and settles into low spots. Plants in these lower areas will be the first to show injury. Plant the most cold hardy plants (carrots, cabbage, etc.) in these low areas in the future. This may stretch your growing season in the higher areas with more tender crops by a week or more. However, if a strong cold front comes through your area, all warm season crops may be injured. If it is cold enough even the cold season crops may show some damage. This is when covering your plants at night may help. Remember to anchor the covering material so that the wind cannot carry it away.

Sweet gum trees will grow in New Mexico, but are not the best trees for fall color

Q. I have sweet gum trees that do not often produce good colors. I know these trees from the Southeastern U.S. where they provide good, consistent fall color. Why do my do so poorly?

Don

Albuquerque

A. Climate, soil conditions, and genetics are the most likely culprits preventing good autumn color in your sweet gum trees. Some trees, even in their native habitat, do not develop good fall color because they are not genetically programmed for these colors. Unless a fall color plant is purchased in the autumn with its color displayed, the buyer does not have any assurance that their plant can develop good color. This is true for some of our native plants that produce fall color. The three-leaf sumac that colors the mountainsides in the fall may produce strong red colors, or poor greenish-yellow colors. Buying them in the autumn helps get the ones that have the best color. However, another consideration for sweet gum and other plants is our soil. Very alkaline soils often inhibit development of good orange and red colors. Soils in the Eastern U.S. are acidic and produce the beautiful reds and oranges. Yellows are more common here in the Western U.S. Finally climate and weather have a great influence on the development of fall color. Sweet gum trees are hardy enough and will grow in Albuquerque and southern New Mexico, but the fall climate is often not conducive to good fall color development. Our dry weather and dry air are one climatic factor that differs from the Southeast. The rapid onset of cold weather can prevent good color development. With all that said, there are some trees that occasionally develop nice purples and reds. That is because; a few autumns provide the conditions that allow for color development, if soil conditions and genetics permit the development of color. There are other trees more likely to consistently produce fall color in New Mexico (Texas red oaks, some Chinkapin oaks, Chinese pistache, aspen and big tooth maple in the right locations).

For more gardening information, visit the NMSU Extension publications World Wide Web site at http://www.cahe.nmsu.edu/pubs/_h or http://aces.nmsu.edu/pubs/periodicals.html

Send your gardening questions to:

Yard and Garden, ATTN: Dr. Curtis Smith
NMSU Cooperative Extension Service
9301 Indian School Road, NE, Suite 112
Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.