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January 14, 2012

Cold frame gardening can be fun and extend the New Mexico gardening season

Yard and Garden
January 14, 2012

Q.
I am getting as a gift, a cold frame that is 6' x 2' with an approximate 28" height. I have gardened for some time, but do not have any experience with extending the season via cold frames. Can you suggest good vegetables to try both in early spring and in the fall?

Mary M. P.
Albuquerque NE heights


A.
Congratulations! I am envious. Since my retirement , I have wanted to build a cold frame, but have stayed too busy to get it done. It will happen someday.

Through even the coldest months of the year you can probably grow kale, cabbage, collards, carrots, radishes, onions, and even lettuce in the cold frame. Many herbs will also grow through the winter in a cold frame. The best plants to grow in the cold frame depend on the location of the cold frame, the amount of sunlight it receives, the heat it generates during the day, and how much heat it can store in the cold frame at night.

Night temperatures in a cold frame are important, but somewhat manageable. Milk jugs, pop bottles, etc. painted black and filled with water, placed near plants in the cold frame will help moderate temperatures inside the cold frame. Many of the plants I mentioned above can tolerate temperatures to about 20 and perhaps colder for short periods of time. Lettuce should stay above 25 to 28 degrees. All of the plants listed above, except carrots and radishes, should be started indoors and transplanted to the cold frame for quicker growth and development. Soil heating cables (available at many horticultural supply websites and nurseries) can be used around tender plants during critical times. These often have thermostats built into them to turn on at about 60 degrees and off at about 70-75 degrees. If you use these, your cold frame becomes a hot bed. A 100 watt incandescent light bulb may also be used to provide nighttime heating in emergencies.

As the season progresses and temperatures begin warming, you can plant tomatoes and chiles in the cold frame. You can use the cold frame as a growing space to let the plants get larger before planting them into the garden, this extends the season and results in tomatoes and chiles earlier. Or, you can plant into the soil in the cold frame and remove the cold frame (or its top) after freezing ends so that the plants can continue to grow in that location. This will allow you to plant 1 to 2 months earlier and begin harvesting much earlier.

A cold frame is a useful “houseplant hospital” during the warmer days in the winter. Plants suffering indoors from low light and dry air can recuperate in the cold frame. Plants can be rotated from the house to the cold frame and back throughout the winter, at least during times when the temperatures in the cold frame are appropriate. You may need to provide some shade for houseplants when they are first brought from the house to the cold frame since they will not be adapted to the full sunlight intensity in the cold fame.

In addition to appropriate watering and fertilizing for the plants in the cold frame, day temperatures can be an issue to watch closely. Cold frames can become too hot very quickly in our intense New Mexico sunlight, so daytime ventilation (and/or shading) becomes important. The bottles of water storing heat in the cold frame are also “sinks” for that heat and slow the heating of the cold frame during the day. This gives you a little more time before venting the cold frame becomes essential.

If insects and diseases build up in the cold frame, you can “purify” the cold frame by removing all plants, closing the cold frame and allowing the temperatures to climb to at least 130 degrees for an hour or so. That should kill most insects and diseases. Higher temperatures (to 160 degrees) or longer durations will pasteurize the soil surface even more thoroughly, but may cause warping of the cold frame structure (check your instructions about this). You can also cleanse surfaces with 10 percent chlorine bleach solution (unless the cold frame directions advise against bleach).

Cold frame gardening will be a lot of fun and I wish you the best gardening in your new cold frame garden.

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW, Los Lunas, NM 87031

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist emeritus with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.