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Hardy, Half-hardy, and Tender Vegetable Crops

Crop protection with fabric tunnels1
Portable tunnels protect crops
Portable tunnels protect crops

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 a cold snap.

Half-hardy is a term used describes 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 (started 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 coldframe and exposed to lower temperatures gradually.
  • Plants in a coldframe can be set outside during the day and covered with a floating row cover then returned to the coldframe 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 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 a few hours the first day, 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 wind 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 warms 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.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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    • Bush beans and pole beans are tender crops. Peas are a cool-season crop but cannot withstand freezing temperatures. Carrots, turnips,rutabagas, beets, and radishes are half-hardy early in life; seedlings should be protected from temperatures lower than 40F; these crops can withstand a light freeze once mature but should be harvested before the soil freezes in late autumn or winter.

  1. So does it equally means that hardy plants can not survive very hot temperature, let’s say 40 degree centigrade? But tenders can?

    • Hardy is a relative term for a plant’s ability to survive cold or hot temperatures–though the term usually applies to cold–thus you often see “cold hardy”. Some warm-season vegetables can survive 40F (104F); however, they will be severely stressed. Most warm-weather vegetables quit growing and slip into a sort of dormancy once temperatures hit the mid-90sF.

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