Harden Off Seedlings Before Transplanting Outdoors

Gradually acclimate indoor-grown seedlings to outdoor conditions over 7 to 14 days before planting them in the garden. Start by placing them in a shaded, sheltered spot for two to three hours on the first day, then increase sun exposure and duration each day until they spend a full day and night outside.

Why It Works

Indoor seedlings have thin cuticles and have never experienced direct sun, wind, or temperature swings. Sudden exposure causes sunburn, wilting, and transplant shock that can stunt or kill plants. Gradual hardening triggers the plant to thicken its cell walls and produce protective compounds, resulting in a resilient transplant.

Tips

• Bring seedlings inside if frost, heavy rain, or strong winds are forecast during the hardening period
• Water seedlings well before each outdoor session to reduce wilting stress
• A cold frame makes hardening off easier by providing a controlled transition environment