Spring is the season that brings the most unpredictable weather. Summer settles into heat. Autumn’s air slowly cools the earth. Winter snuggles down for its long nap, but spring’s warming trend is often reminiscent of a roller coaster! Warm days followed by cool nights followed by cold days and warm nights. The promise of sun teases the daffodils. From one day to the next, in spring it is difficult to foresee tomorrow’s climatic condition.
Professional growers are well aware of the uncertain temperatures and take few risks for their livelihood depends upon selling their crop rather than losing it to a freeze. You, the home gardener, may not have as much to lose, but no gardener wants to see their baby tomatoes or peppers succumb to a frosty night.
The process of slowly allowing a plant to adapt to fluctuating temperature is known as hardening off. It is simple enough, usually consisting of bringing a flat of seedlings out in the morning and inside come evening. Multiple flats may be hardened off by opening a window or door to create a cool draft on the plants.
Seedlings are fragile. Allow a young plant to develop its first or second true leaves before beginning this process. (The “foliage” that appears when a seed first sprouts is not its true leaves.) Increase the plants’ exposure to temperature change gradually as the plants grow in size. An extra warm, sunny day can be just as deadly to a seedling as a cold night.
Strengthen a seedling by gently brushing your hand over the foliage. This movement (an imitation of wind) will help bring essential strength to the main stalk. A tomato seedling with a weak stem does not show the same vigor or growth as the same variety with a stout stalk.
Be aware of some plant tolerances where cold is concerned. For instance, a tomato is slowed but not deterred by a 38- or 40-degree night. That same temperature will probably stunt a pepper, taking it longer to recover and resume growth. Often young plants set out at a later date will surpass an early planting for their growth can begin and continues without interruption.
A good rule of thumb is to find out the origin of the plants you want to grow. Tomatoes and peppers originated in South America and were domesticated in Mexico; they like warm weather. Celery comes from Britain, broccoli from northern Europe and cabbage from Germany; all three are cool weather crops. With all the marvels of science, temperature adaptation is still found in the genetic make-up of a plant.
LeeAnn Barton has worked with nurseries for more than 20 years. She digs in the dirt in Stillwater. Direct any questions to her, especially about tree selection, by emailing firstname.lastname@example.org.