Hardening off means acclimating soft and tender growth-which has been protected from wind, cold, and strong sun-to outdoor conditions. Start the process of hardening off about 2 weeks before you intend to plant the seedlings outside. Water your seedlings well, then set them outdoors in a partially shaded spot. Leave the seedlings out for about an hour the first time. Repeat this process daily, gradually working up to a full day by the time they are scheduled to be transplanted into the garden. There's no rush to set your plants out. If they're frost-tender, be sure that all danger of frost has passed. Transplant on a cloudy day, so strong sun won't wilt your seedlings.