Hardening Off Greenhouse Plants

In northern climates, cool spring temperatures, strong winds and bright sun can be very stressful to plants that have been grown in a greenhouse.

To minimize these risks to tender plants a process known as “hardening off” is required.

Steps to Hardening Off Plants

• • Set outdoors in a sheltered area a couple of hours on nice mild day and return indoors at night.
    • Indoors could be the garage or garden shed if it’s a mild night.
    • It’s important to protect the plants from strong sun, wind, cool temperatures, and heavy rains.
  • Each day the plants can be exposed to one more hour of direct light.
    • Each night, move the plants back to a sheltered enclosed environment.
  • The process can take 7 to 14 days depending on weather conditions and the variety of plant.
  • During the hardening off process, carefully watch the weather forecast, especially the first few days; if strong storms or low temperatures are forecast, keep the plants inside.
  • Plants that are perennial but forced in a greenhouse will handle temperature down to 33°F but will benefit with a plant cover, like a cardboard box or an old nursery pot.
  • After the hardening off process is completed, your plants will be able to tolerate most of spring’s unpredictable weather but continue to take steps to lessen their exposure to extreme conditions.