How to Successfully Harden Off Plants

Kyle Barnhart

Young plants grown in a greenhouse will need a period to adjust and acclimate to outdoor conditions, prior to planting in the garden. This transition period is called "hardening off".

Young plants grown in a greenhouse will need a period to adjust and acclimate to outdoor conditions, prior to planting in the garden. This transition period is called "hardening off".

Hardening off gradually exposes the plants to the wind, the sun, and rain and toughens them up by thickening the cuticle on the leaves so that the leaves lose less water when exposed to the elements. This helps prevent transplant shock.

The length of time a plant requires to harden off depends on the type of plants you are growing and the temperature and temperature fluctuations. So be flexible when hardening off your plants and be prepared to whisk them indoors or cover them if there is a late freeze or snow.

Gradually Exposing Plants to Longer Periods of Time Outdoors

  • Begin putting your seedlings outdoors about several days before your actual plan on planting them outside
  • Place the plants in a sheltered, shady spot outdoors.  Start by leaving them outdoors for 3 - 4 hours and gradually increase the time spent outside.
  • Bring the plants back indoors, or somewhere warm like a heated garage or porch, each night.
  • A day or two before you plan on planting outside, put the plants in a more sunny location during the day.
  • If temperatures remain warm both day and night, (at least 50F.), the plants should be able to handle the sun all day and stay out at night after about 4-5 days, Keep an eye out that the soil doesn't dry in their small pots and bake the plants if the weather should suddenly turn warmer
  • By taking the time to harden your plants off you will help adapt to being outside and to their home for the summer.  Have any further questions, please contact us at guiniridge@gmail.com or (207) 877-5874.

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