How to Harden Plants for the Garden

Harden off seedlings before planting outside.

Hardening off seedlings is done in the early spring just before it's time to transplant into the garden or into a container. The term "hardening off" means to give transplants a head start before being planted. The seedlings have been growing in a comfortable atmosphere for six to eight weeks and it will shock them if they are suddenly placed outside. This method will help sensitive seedlings adapt to their new environments a little bit at a time over the period of one week to 10 days.

Things You'll Need

• Seedlings in flats or seedling trays
• Garden gloves
• Trowel

Instructions

1. Run a knife down to the bottom of the flat in between the plants to root prune one week before starting to harden off. This is done only for seedlings that have been planted in flats and will help separate the plants when transplanting is done. If you have planted seedlings in six packs or other seedling trays, this step isn't necessary.

2. Take seedlings outside and set in a semi-shady area on the first day of hardening off. They should be left outside only for a few hours.

3. Increase the amount of sun exposure and time outdoors for your seedlings every day. Reduce watering but do not let the seedlings wilt.

4. After seedlings have been acclimated outside for a week to 10 days, use your garden gloves and trowel and plant them into your garden where they'll be for the growing season.

Tips & Warnings

• Keep an eye on the weather forecast for low temperatures. If a frost is predicted and the seedlings haven't been planted in the ground yet, bring them back inside for the night.

References

• Washington State University: Hardening Off Transplants
• Colorado State University: Hardening Off Isn't Hard