How to Harden Off Greenhouse Plants

Introduce greenhouse plants slowly to the outdoors.

Plants that are grown inside a greenhouse become accustomed to consistent temperature, humidity and light levels. If you move these plants outside of the greenhouse and into the ground, they often suffer from shock due to the wide fluctuations in conditions. Instead, you must harden off the greenhouse plants, or slowly introduce them to the outside elements. This increases the survival rate of the plants once they are eventually placed in the ground.

Instructions

1. Wait until all chances of frost have passed for your area to begin the hardening off process.

2. Look for outdoor location that has filtered sunlight, not direct sunlight. Place the greenhouse plants in this location and allow them to remain there for two to three hours. After this time, move them back inside the greenhouse until the next day.

3. Place the plants outdoors the following day and increase the time they are left outside to between four and six hours. Move the plants back inside the greenhouse after this time period.

4. Continue increasing the time period that the plants are left outdoors by two to three hours per day for one week.

5. Locate an area of the yard that has full shade, such as under a tree or an awning. Set the greenhouse plants on the ground in the area and leave them there for one week. During this time, add additional water to the pots if needed.

6. Plant the greenhouse plants in their permanent ground location after they have been outdoors in the shade for one week.

Tips & Warnings

• The plants will require more frequent watering once you begin placing them outside because water evaporates more quickly outdoors, especially if it is windy.

• Monitor the weather forecast diligently during the hardening off period and do not place the plants outside if temperatures are expected to drop near freezing.

• Home vegetable gardeners must complete the same hardening off process before planting seedlings outdoors.

References

• Greenhouse Growing Pricking Out, Potting and Hardening Off Greenhouse Plants
• Washington State University: Hardening off Transplants