Hardy is a term used to describe a plant’s ability to survive in a specific climate zone—even through the cold of winter. Commonly gardeners use the term “hardy” to describe a plant that can survive a freeze, frost, or cold snap.
Half-hardy is a term used to describe plants that can survive only limited or light frost—meaning just an hour or two of frost or near-freezing temperatures. Half-hardy plants must be protected from anything more than a touch of frost.
Tender is a word used to describe plants that are injured by frost or cold weather. Tender plants must be protected from temperatures near freezing.
Hardy, half-hardy, and tender vegetable crops:
- Hardy vegetables: broccoli, Brussels sprouts, cabbage, collard, kale, kohlrabi, leek, onion, and spinach.
- Half-hardy vegetables: cauliflower, celery, chard, chicory, Chinese cabbage, endive, and lettuce.
- Tender vegetables: cucumber, eggplant, muskmelon, okra, pepper, pumpkin, squash, tomato, and watermelon.
Hardening off young plants
Hardening describes the process of preparing young plants (starting from seed indoors) for outside weather conditions. Young plants can be acclimatized to lower temperatures and exposure in several ways:
- Young plants can be moved from a greenhouse or indoors to a cold frame and exposed to lower temperatures gradually.
- Plants in a cold frame can be set outside during the day and covered with a floating row cover then returned to the cold frame at night.
- Plants in the garden can be protected by cloches or movable fabric or plastic tunnels at night and exposed to the elements during the day.
- During hardening off, protect plants not only from the cold but also from full sun and wind—all of which can cause young plants distress. Use shade cloth a tunnel covered with garden fabric or a lean-to made of lath to buffer wind and sun.
Hardening off is commonly done over a period of three to five days before transplanting. Harden off young plants for a few hours the first day, and add more hours each day until the plant is exposed to the outdoors for six to eight hours.
Cloches and tunnels to protect young plants
Protective coverings can raise the temperature around young plants and half-hardy and tender plants by 5 to 20 degrees Fahrenheit or more. Temporary and easily movable coverings are useful where the weather warms up, then is hit by a quick frost, and then warms up again. Place protective coverings over young plants that are hardening off and over tender and half-hardy plants when nighttime temperatures may dip.
Here are two simple and easy-to-move and store plant coverings:
Cloche. Cloche is any covering that allows sunlight to reach a plant but keeps cool temperatures and winds away. A simple cloche is made by removing the bottom from a plastic jug and setting it over a plant. A cloche traps heat and warm the soil and air under it.
Plastic or fabric tunnel. Tunnels made from sheet plastic or garden fabric stretched across arched construction or chicken wire, wire wickets, or over hoops of PVC tubing can cover rows of young seedlings or new transplants. Portable tunnels can be 1 to 3 feet wide and 10 to even 15 feet long. Plastic tunnels can be as much as 10 to 20 degrees warmer than the outside temperature and give half-hardy and tender plants a one to two-week head start on the season.