What is considered in hardening off:
There are 3 approaches to hardening off:
Gradually Longer periods of Time Outdoors
Place in a Cold Frame
Withholding Water
Allowing seedlings to wilt has the same effect as gradually exposing them to the elements.
Tips
- Sun – a plant just out of a greenhouse will sunburn if not hardened off first. (Think of sitting on the beach all day after a winter in the office.)
- Wind – a plant will wilt in the wind if not hardened off; foliage can become wind burned; breakage can also occur. Do not start to harden off plants on a very windy day or a very windy location.
- Cold – a plant grown in a warm greenhouse or house will not tolerate cold as well as a plant that has gotten used to the cold slowly. (You feel cold at 45 degrees in July, but 45 degrees in January may feel warm!) Get your plants used to cooler/colder temps before planting out. A “winter hardy plant” can die in a frost if it hasn’t been acclimated to cold temperatures.
- Start the hardening off process on a mild day that is neither too windy nor too cold.
- Put the plants out in the spot that they will eventually reside, but just for an hour or two; then move them into a shady and less windy spot.
- The next day, double the time out in the sun and wind before putting them back in a sheltered spot.
- The third day, double the time again.
- By the 4th day they are usually tough enough to be planted in the ground.
There are 3 approaches to hardening off:
- Gradually Longer periods of Time Outdoors
- Place in a Cold Frame
- Withholding Water
Gradually Longer periods of Time Outdoors
- Begin 7 - 10 days before your transplant date.
- Place plants in a sheltered, shady spot outdoors. Under a tree or even on your back porch is fine. Leave them for 3-4 hours and gradually increase the time spent outside by 1-2 hours per day.
- Bring plants back indoors each night.
- After 2-3 days, move the plants from their shady spot into morning sun, return them to the shade in the afternoon.
- After 7 days, the plants should be able to handle sun all day and stay out at night, if temperatures stay around 50 degrees F. Keep an eye out that the soil doesn't dry and bake the plants, if the weather is warm.
- After 7 -10 days your plants are ready to transplant. Try to do so on a cloudy day and be sure to water well after planting.
Place in a Cold Frame
- Begin 7 - 10 days before your transplant date.
- Indoor grown plants can be moved and left in a cold frame, for hardening off.
- Turn off heating cables and/or open the cold frame cover for gradually longer periods of time. Start with 3-4 hours and gradually increase the exposure time by 1-2 hours per day.
- Close the cover and resume heating at night, if temperatures dip below about 40 degrees F.
- Plants should be ready to transplant in 7 - 10 days. Try to do so on a cloudy day and be sure to water well after planting.
Withholding Water
Allowing seedlings to wilt has the same effect as gradually exposing them to the elements.
- Starting about 2 weeks before your transplant date, don't water your seedlings until they start to wilt.
- At this point, water normally, then wait for them to wilt again.
- After 2 weeks of this process, seedlings should be ready to transplant. Try to do so on a cloudy day and be sure to water well after planting.
Tips
- The moving in and out process can be made easier by putting your plants on a wagon or wheelbarrow and simply wheeling them into the garage for the night.
- Protect your young seedlings from animals and snails or slugs.
