Hardening Off Plants and Seedlings

Reader Contribution by Rebecca Martin
Published on July 13, 2016
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Planting the seedlings you’ve raised carefully indoors is a proud moment. But be sure to acclimatize them to their new outdoor home first, or you’ll risk losing your plants and wasting all that hard work. This is a process known to gardeners as hardening off plants.

Start hardening off your seedlings about a week before the final frost date for your area. Our Garden Planner uses data from your nearest weather station to give an indication of when it’s safe to plant outside.

Choose a sheltered spot to harden off plants, and start hardening off on a still, cloudy day when temperatures are fairly steady. Water the seedlings before they go outside so there’s less risk of them drying out. Avoid placing plants on the ground where they can easily be knocked over by birds or nibbled on by slugs.

An unheated greenhouse or cold frame is a great tool for hardening off transplants. Place seedlings and plants into the structure for a couple of hours on the first day, then gradually increase the length of time they’re in place by two or more hours per day. After a week they can then be left there overnight, as long as there’s no danger of frost.

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