How to "Harden Off" Seedlings before Transplanting

If you're going seedlings indoors, they've been pampered all winter/spring.  Aside from the random cat attack or possibly too much watering, they have been relatively safe compared to the dangers that await them in the great outdoors.

Hardening off gradually exposes the tender plants to wind, sun and rain and toughens them up by thickening the cuticle on the leaves so that the leaves lose less water. This helps prevent transplant shock; seedlings that languish, become stunted or die from sudden changes in temperature.  

Hardening off times depend on the type of plants you are growing and the temperature and temperature fluctuations. So be flexible when hardening off your seedlings and be prepared to whisk them indoors if there's a late freeze and snow.

Not everyone grows seedlings indoors.  Even some of my seedlings that were grown outside needed to be acclimated to their new are before being transplanted.

From VegetableGardener.com,

One Way to Harden Off Seedlings

Through your own experimentation in your specific zone you'll come up with your personal technique for hardening off seedlings, but until then here's what I do:

1. Take my little ones outdoors under a protected/covered area for a couple of hours to start a 7 to 14 day hardening off process. 
Remember that this is under cover, not in a sunny spot in the yard. My preference is to get the seedlings used to the temperatures and breezes before I introduce the sun. After 2-3 hours, I bring them back inside.
2. After a couple of days vacationing in a shaded area, I place them out in the light for 1 hour (usually be morning sun because it's a gentler light than the afternoons sun). After their daily dose of sun, I pull them back into the shaded area until evening -- then I bring them back into the house.

3. Day after day, I increase the time that they spend in the sun. After about a week, I let them spend the night outdoors in the covered or protected area.

4. The time they spend in the sun becomes longer and longer until I hit about two weeks after I first began the process. At this point I'm confident that they're ready to take on the world in their garden bed.

HELPFUL LINKS:

Growing Heirloom Tomatoes from Seed to Harvest

The Importance of Soil

Using Coconut Coir in the Garden

MAY Seed Planting Guide for the US (by region)

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