How long should seedlings undergo hardening off?

Hardening off seedlings is timing-specific for success. Most plants should be provided with an outdoor exposure of 7 to 14 days. The actual time depends on plant type and weather conditions. A too brief period gives rise to shock; a too long period produces delayed growth. For hardening the seedlings, I adjust my timetable according to whether the daily temperature reading is high or low.

Different varieties of plants have different hardening requirements. Tough vegetables like kale can take up to seven days to harden. Tender vegetables like tomatoes require ten to fourteen days. Tender herbs like basil need the full two weeks. I group the plants by type to manage my schedule effectively. Weather changes everything and requires one to extend the hardening schedules during cold snaps.

Watch for readiness signs in plants. Hardened seedlings stand up in the wind. They are dark green without spots on the leaves, and the stems are firm, not brittle. They withstand dew without damage. Harden them longer if they droop or appear pale. For surprises, keep row covers on hand.

Longer hardening periods are needed in cloudy weather because plants receive less UV light. A week of rain may lengthen the process by 3 days. Under nice, warm, sunny spring days, the hardening may be finished quickly as well. The reactions of the plants should be the first consideration, not the calendar.

Read the full article: The Complete Guide to Hardening Off Seedlings