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

by Curtis Smith, PhD, NMSU Extension Specialist

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. (continued at SW Yard and Garden column January 2, 2010)