Updated: May 2, 2022
You have so carefully planted and cared for your seedlings indoors and now you want to prepare them for surviving the transition to outdoors. How do we go about moving them from inside, into our garden without them dying? They need to be carefully hardened off (climatized) to sun, wind and cool temperatures. Skipping this step all too often ends in disaster.
What Does Hardening Off Plants Mean?
The phrase "Hardening Off Plants" means slowly transitioning plants to adjust to the cooler temperatures during the night and the strength of the sun and the wind so that they can be moved from in a house or in a greenhouse to outdoors without shocking the plants.
The hardening off process should take approximately a week. To move plants directly from your house into your garden would likely give your plants a shock that will either kill them or stunt them and cause the plants to stop growing for a few weeks, thus losing all that hard work of getting ahead by starting seedlings early in your house.
Following are methods for hardening off your plants with no greenhouse as well as hardening off plants using different types of greenhouses. Take care not to break your plants when moving them in and out of the house during the hardening off phase. If you notice the leaves begin to get white or yellow spots on them, take a break from the direct sunlight and back up two days in your hardening off schedule. If at anytime the temperature is expected to fall below freezing or if high winds develop, bring plants indoors.
After completing the week of transition your plants are ready to be permanently planted in your garden. This does not mean they will survive a frost. If there is a late forecasted frost, cover your plants with a blanket, towel or plastic for the duration of the freezing temperatures. These are guidelines and may be adjusted as needed. (Find tips for covering your plants here.)
How to Harden off Plants Without a Greenhouse
If you are not using a greenhouse to harden off your plants, follow this schedule.
Day 1 - 4 hours in the shade outdoors and then bring plants back inside.
Day 2 - 1 hour in the sun and 3 hours in the shade outdoors and then bring plants back inside.
Day 3 - 2 hours in the sun and 4 hours in the shade outdoors and then bring plants back inside.