NMSU branding

Issue: January 2, 2010

Some warm season vegetable seed need a little extra warmth to germinate early in a cool home.

Q. I want to start my vegetable transplants early, but some seeds (especially tomatoes and chiles) are not germinating. They are in my house on top of the refrigerator like some garden books recommend. I keep my house cool to save energy. Could the fact that my house is quite cool have anything to do with the slow germination of the seeds? Is there anything I can do to make these seeds germinate?

Jason R.

A. A cool home may indeed slow the germination of some garden seeds. Some vegetable and flower seeds will germinate at cool temperatures, but others need to be quite warm to germinate quickly. Many years ago, the top of a refrigerator was recommended as a good place to germinate seeds but modern refrigerators are better insulated and rarely radiate heat from the top, so this may not be the best place to start seeds.

Even in the garden, tomato and especially chile seeds are slow to germinate until the soil has warmed. Research at NMSU has shown that the best conditions for chile seed germination is a day temperature of 86 degrees alternating with a night temperature of 59 degrees under conditions of 16 hours of (artificial) light and 8 hours of darkness. However, other research has shown good germination of chile seeds at a constant temperature of 68 degrees. Germination was poorer at lower temperatures. These same temperatures will be adequate for germinating tomato seeds as well.

A horticultural electric heating pad will effectively provide warm germination temperatures. Such pads can be purchased from several garden and greenhouse supply sources. These small heating pads use relatively little electricity because they are only heating a very small area. The gentle heat provided by the heating pad can greatly speed the germination of seeds of warm season vegetables such as chile and tomato plants. Some people have recommended using heating pads that may be bought at a pharmacy or an electric blanket, but such heating pads are not meant for use in the presence of water and soil. Since electricity is involved and water is needed for germinating seeds, it is best to purchase a heating pad meant for the moist horticultural environment. The proper heating pads are much safer for you and your home.

Bottom heat as provided by horticultural heating pads can be use to facilitate the starting of plants from cuttings and to speed the growth of seedlings in addition to increasing the speed of seed germination. Serious gardeners may consider horticultural heating pads to provide bottom heat a desirable addition to their set of garden tools.

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

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.