If you’ve started some plants from seed or purchased some from your garden center, you’re probably eager to get them in the ground. If you want to get them off to the best start possible, however, it pays to take a few days to get them ready.
What is Hardening Off
Hardening off is the process of acclimating your plants to the outside environment before you put them in their permanent home.
The indoor environment is a much gentler environment than they will be exposed to outdoors, even if they were raised in a window or a greenhouse. A gradual introduction to the new environment will reduce damage from wind and sunscald and lower the risk of transplant shock. Think of it as a base tan.
The Hardening Off Process
Plants are placed in a sheltered outdoor situation that gradually increases their exposure to the elements. First, we expose the plants to just a few hours of sunlight and fresh air. Each day we increase the amount of exposure they receive by an hour or two until they’ve been out for a full day and night. Then they are ready for transplanting.
Tips for Hardening Off Success
Ensure your plants are ready for transplanting. They should have several true leaves and be reasonably healthy. If they are looking leggy, weak, or damaged, give them some tender loving care before putting them outdoors.
When the outdoor temperatures are suitable for your plants, choose an outdoor spot where they can rest for a few days. It should get partial sunlight and be sheltered from severe winds.
Remember also that critters are interested in your plants so keep them off the ground and protect them as best you can.
Place your plants in direct sunlight for no more than three hours a day and increase by 2-3 hour increments each day. Starting on an overcast day will make it easier for your plants.
If at any time your plants start to look crispy or otherwise unhealthy, don’t increase their stress right away. Give them the same amount of exposure or a little less than they had yesterday to give them a chance to catch up.
If you don’t have time or energy to haul all of your plants in and out every day, place your plants in a sheltered area that gets shaded part of the day. The morning sun is gentler than the afternoon and evening sun, so starting near the Eastern side (Western in the Southern Hemisphere) of the house is ideal.
If you put your plants in a wagon, you can start them off in a sheltered, shady spot and then just move them a little bit further out of the shade each day.
If you place your plants in a dog crate, they are protected from critters and you can use a tarp to protect them from severe rain and wind and control the amount of sunlight they get.
If temperatures drop below 40 degrees Fahrenheit on your cold-hardy annuals (cabbage, onions, lettuce) or 65 degrees on your heat-loving cold-tender annuals (peppers, tomatoes, squash), bring them back inside until it warms up.