Hardening Off Vegetable Plants

I’ve gone from seeds sprouted under lights, move them to the greenhouse and gave them a little more root room by potting them up in larger containers. Now it’s time to harden them off before planting in the garden beds.

This is called cold hardening or hardening off and is done by gradually moving the flats from inside to outside and shade to sun over the course of 7 to 10 days.

To do this, move the plants to a shady area for 1 to 3 hours the first day. Move the plants back indoors at night. Increase the time outside in the shade 1 to 2 hours the next day.

On day three, move the plants to morning sun for 3 hours and then back to shade in the afternoon. Gradually increase the time in the sun by an hour a day. If you do this too quickly, the plants could sunburn. By day 7, the plants can handle full sun all day and stay out at night. If the temps dip below 40, move the plants to a sheltered area or indoors for the night.

By day 10, the plants are ready for transplanting into the garden. Watch the local weather and be prepared to protect them if a late frost is predicted. If possible, choose a cloudy day to transplant and water thoroughly after planting.

For a scientific explanation on why this is a necessary step, read here. and here. Damage to the plants can occur with temperatures below 50 if the they aren’t properly prepared.

Waiting for the sun.

Although my plants have been in the greenhouse for several weeks, they still need to transition to the cooler temps and brighter sunlight outside. Since the greenhouse is unheated, I’m pretty confident that they are through the first stages of temperature acclimation. I moved them 3 days ago to a shady location against our brick house that gets very late afternoon sun and they’ve been out left out at night. I’ll be moving them to a sunnier location gradually over the next few days and will be planted in the garden this weekend.