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How to Harden Off Plants

Preparing Seedlings to be Planted Outdoors

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The Spruce / Randi Biedermann

Young, pampered seedlings that were grown either indoors or in a greenhouse will need an adjustment period to acclimate to outdoor conditions before being planted in the garden. This transition period is called “hardening off.”  

Hardening off seedlings gradually exposes the tender plants to the wind, sun, and rain. toughening them up by thickening the cuticle on the leaves so they lose less water when exposed to the elements. This helps prevent transplant shock, the term used for seedlings that languish, become stunted, or die from sudden changes in temperature and exposure to sunlight.

The length of time a seedling requires to harden off depends on the type of plants being grown as well as the outdoor temperatures. Be flexible when hardening off your seedlings and prepare to whisk them indoors or cover them if a a late spring freeze or snow is in the forecast.

Choose either of the following methods to harden off seedlings:

Learn here about the three approaches to hardening off, methods for making your seedlings adjust and acclimate to outdoor conditions.