Hardening Off Seedlings
Technique
Hardening off is the process of gradually adjusting indoor-grown seedlings to outdoor conditions. This step reduces transplant shock from sun, wind, and temperature changes.
How to do it
Set seedlings outdoors in a protected, shaded spot for a short period the first day. Increase outdoor time a little each day, slowly exposing plants to more sun and wind over about a week or more. Bring plants in or protect them if nights are unusually cold or weather turns severe. Keep the potting mix evenly moist during the process so plants are not stressed before transplanting.
Timing
Begin hardening off shortly before your planned transplant date, usually after the main frost risk has passed for tender plants. Cool-season crops may tolerate earlier exposure, but they still need a gradual transition. Time the process so seedlings go into the garden soon after they are conditioned.
Tips
Avoid placing tender seedlings into full midday sun on the first day. Watch for wilting, bleaching, or leaf scorch and slow the process if needed. A sheltered porch, cold frame, or shaded patio can make the transition easier.
General guidance for US gardens. Timing depends on your local frost dates and hardiness zone. Page updated Aug 4, 2026.