To harden off seedlings effectively, follow these key steps:
- Start 1-2 weeks before transplanting : Begin the hardening off process about one to two weeks before you plan to move seedlings permanently outdoors
- Gradual outdoor exposure : On warm days (above 45°F), place seedlings outside in a shaded, protected spot for a short time initially—about 1 hour on the first day
. Avoid windy days and temperatures below 45°F to prevent damage
- Increase sunlight and time gradually : Each day, increase the amount of sunlight and time the seedlings spend outside by about one hour, moving from shade to morning sun, then to more direct sunlight
. This helps seedlings adjust from soft, indoor growth to firmer, outdoor growth.
- Bring seedlings indoors at night : To protect them from cold or harsh conditions, bring seedlings inside or into a protected area overnight until they are fully hardened
- Reduce watering and fertilizing before starting : About a week before hardening off, stop fertilizing and reduce watering to slow growth and encourage stronger root development
- Use protection if needed : If temperatures stay above 50°F at night, seedlings can eventually be left outside overnight. Using shade cloth or a cold frame can help protect seedlings during the transition
- Transplant after 7-14 days : After about one to two weeks of gradually increasing outdoor exposure, seedlings should be ready to plant in the garden
A simple example schedule might be:
- Day 1: 1 hour outside in shade
- Day 2: 2 hours outside, some morning sun
- Day 3: 3-4 hours outside, more sun exposure
- Continue increasing time and sun exposure daily until seedlings can stay outdoors all day and overnight
This process reduces transplant shock by toughening seedlings to wind, sun, and temperature changes, helping them thrive once planted outdoors
