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Before you plant your plant starts outside....

Before you Plant– Hardening Off Plants

Hardening off your plants prepares them for the real world of hot sun, rough winds, cold nights, and variable rain. Most perennials in our climate have already been hardened outdoors or in unheated greenhouses, they are ready for planting. In contrast, veggie starts, tomato plants, annual herbs and flowers have probably never left their heated greenhouses. Therefore, for any plants raised in a greenhouse or at home, we recommend “hardening off” before planting them.


Seedlings such as half-hardy annuals, half-hardy perennials, and many vegetables that are started indoors with heat must be gradually acclimated to direct sunlight, winds, and generally cooler night temperatures of the outdoors prior to planting out in their final locations. This conditioning is known as hardening-off. It takes anywhere from seven to fourteen days.

When seedlings have reached an appropriate size and the timing is right for the individual plants to go outdoors into their final location, start the process of hardening off.

  1. Place pots or flats outdoors for several hours a day in a location of some morning sun and with protection from winds, and severe cold.

  2. Return them to the protection of an unheated porch, garage, or greenhouse in late afternoon and overnight.

  3. Each day, for one to two weeks, increase the amount of time plants are outdoors and increase the light they receive to the appropriate light levels, eventually leaving them outdoors all night.

  4. At the end of the period, and after all risk of frost passes, plants are fully ready to go into the garden. Remember to protect them from predicted freezing winds and heavy rains which can dislodge seedlings.

  5. Protecting new plants can also involve the use of garden fabric, cloches, or plastic sheeting.





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