Issue: December 30, 2006

Starting transplants indoors


Last year I tried to start tomato and chile plants in my home. By the time it was warm enough to plant them outside, they were tall and skinny. Only a few tomato plants survived. What did I do wrong?


The plants did not receive enough light. Once the seeds have germinated the plants need light to develop into healthy transplants. A small window will not provide enough light. The young plants will need at least 4 hours of bright light each day. A south-facing window will be the best location, but it should be a large window. Direct exposure to sunlight does not provide the best light. Light that is slightly filtered (through lace or sheer curtains) will be better.

The room temperature should be fairly low. Night temperatures as low as 60 degrees F. are excellent and day temperatures should not exceed 80 degrees. These temperatures will allow development of stout plants that will transplant more easily.

Your transplants should be started about 6 weeks before you will plant them outside. You can start them earlier if you have room to transplant them into fairly large pots while they are growing indoors. As the time to transplant these plants into the garden approaches, you should begin to “harden” the plants to the conditions outside. That means place them outside into gradually increasing light intensities and durations in direct sunlight. The plants must also become adapted to the dry air and temperatures outside. If a frost is predicted, don’t leave them outside; otherwise, leave them outside as much as possible.

The tomatoes have a useful ability to develop roots along their stems if they are planted deeply. If the plants are tall and skinny, just plant them deeply and allow them to root along the length of the buried stems. Chiles and many other vegetables do not have this ability, so only do this with the tomatoes.

If you did not have a chance to sufficiently adapt your plants to the outside environment before planting them in the garden, you can use branches pruned from shrubs and trees to create shade over the new transplants for the first few weeks they are in the garden. Just stick the stems pruned from the trees and shrubs into the ground near the tomatoes and chiles so that they are firmly supported and will shade the new transplants. This also works well for nursery grown transplants that have been produced in a protected greenhouse environment.

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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:, office: 505-865-7340, ext. 113.


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

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