In the Garden:
One of my raised beds, covered with plastic, is a perfect place to harden off seedlings in preparation for their move to the garden.
Physically Fit Seedlings
Whether you start seeds indoors yourself or buy your seedlings at the garden center, all young plants benefit from two to three weeks of conditioning before they are set free in the garden. This process, called hardening off, affects every part of the plant leaf, stem, and root and results in rougher, tougher seedlings that have what it takes to thrive in the garden.
The light plants receive indoors or in a greenhouse is not nearly as intense as bona-fide outdoor sun. Making the transition requires a couple of physical changes on the part of the plants. They must thicken up their leaf cuticles, and they must rearrange their cells into more numerous layers. By gradually increasing the amount of sun your seedlings receive, you will support these two important adaptive talents. Once hardening off is under way, don't be surprised if new leaves are slightly smaller in size. This is good! It's a sign that the leaves are getting ready for life outside.
Sturdy Stems, Resilient Roots
Windless environments encourage plants to grow long cells in their stems, but this quickly changes when motion becomes an everyday part of their lives. When you jiggle your seedlings, plants respond by growing stronger stems. During hardening off, gentle winds continue this process, which affects the roots, too. You might think of movement as the factor that gives stems muscle and improves the anchor strength of roots. Yet it's important to let plants become accustomed to moving air very gradually. On very windy days, it's often best to bring the babies in and give them a day of rest.
During hardening off, let your plants learn how to adapt to short periods of dryness by watering them a little less. After the first week, start leaving them outdoors on mild nights, too -- the last step in spring training for seedlings.
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