Recent frost advisories are relevant for late-season vegetables.
Posted on October 13, 2014 by Ben Phillips, Michigan State University Extension
A "water-soaked" appearance is a common identifier of freeze damage on fruiting vegetables. These decorative gourds will still harden off, but the discoloration is permanent. Photo by Ben Phillips, MSU Extension
Plant hardiness
Depending on crop tolerance, a killing frost can result from canopy temperatures dropping 2-5 degrees below freezing for 5-10 minutes, or from a sustained temperature 31.5–32 degrees Fahrenheit lasting 3-5 hours. Fall vegetables have a range of temperature tolerances, reflecting their origin of domestication. Vegetables that come from flowers, such as vine and solanaceous crops, okra, sweet corn and beans, have largely been cultivated and bred from tropical and subtropical plants, and are easily damaged by a light frost (28-32 F).
When freezing occurs, water expands and can burst cell walls. However, leaf and root vegetables are generally more capable of withstanding hard frosts (less than 28 F), and have more room to spare in their tissues for water expansion and internal ice-formation.
Hard frost hardy (less than 28 F)
- Collards
- Endive/escarole
- Kale
- Kohlrabi
- Lettuce
- Mustard
- Onion (sets and seeds)
- Pea
- Potato
- Rhubarb
- Rutabaga
- Spinach
- Turnip
Light frost hardy (28–32 F)
- Beet
- Broccoli
- Cabbage
- Carrot
- Cauliflower
- Celeriac
- Celery
- Chard
- Onion (plants)
- Parsnip
- Radish
Light frost susceptible (28–32 F)
- Cucumber
- Edible beans
- Eggplant
- Muskmelon
- Okra
- Pepper
- Pumpkin
- Squash, summer/winter
- Sweet corn
- Sweet potato
- Tomato
- Watermelon
How to tell if you have frost-damaged vegetables
Freeze-killed leaves will at first turn brown and look somewhat transparent as they thaw, a term generally referred to as "water-soaked.' Once dry, they may curl up and become brittle. The marketable part of the plant may also show signs of damage.
The list below is adapted from Purdue Extension Bulletin HO-203, "Effects of Cold Weather on Horticultural Plants in Indiana,' and describes what to look for in freeze-damaged vegetables. For positive identification of suspected freeze damage, find an expert regional Michigan State University Extension educator.
- Beet: External and internal water-soaking; sometimes blackening of conducting tissue.
- Broccoli: The youngest florets in the center of the curd are most sensitive to freezing injury. They turn brown and give off strong odors upon thawing.
- Cabbage: Leaves become water-soaked, translucent and limp upon thawing; epidermis separates.
- Carrot: Blistered appearance, jagged, length-wise cracks. Interior becomes water-soaked and darkened upon thawing.
- Cauliflower: Curds turn brown and have a strong off-odor when cooked.
- Celery: Leaves and petioles appear wilted and water-soaked upon thawing. Petioles freeze more readily than leaves.
- Cucumber: Transparent, water-soaked appearance in cross section, just under the skin.
- Garlic: Thawed cloves appear grayish-yellow and water-soaked.
- Lettuce: Blistering; dead cells of the separated epidermis on outer leaves become tan; increased susceptibility to physical damage and decay.
- Onion: Thawed bulbs are soft, grayish-yellow and water-soaked in cross section; often limited to individual scales.
- Pepper: Dead, water-soaked tissue in part or all of pericarp surface; pitting, shriveling and decay follow thawing.
- Potato: Freezing injury may not be externally evident, but shows as gray or bluish-gray patches beneath the skin. Thawed tubers become soft and watery.
- Pumpkin: Water-soaked spots on upper surface of fruit which soften the rind. Badly damaged fruit will eventually collapse in on itself.
- Radish: Thawed tissues appear translucent; roots soften and shrivel.
- Squash: Water-soaked spots on upper surface of fruit. Ornamental and winter squashes may still harden, but others will soften and rot.
- Sweet corn: Reduced ear size and weight with shriveled kernels. Ears can take a "bar-bell' shape if they are still developing.
- Sweet potato: A yellowish-brown discoloration of the vascular ring and a yellowish-green, water-soaked appearance of other tissues. Roots soften and become very susceptible to decay.
- Tomato: Water-soaked and soft upon thawing. In partially frozen fruits, the margin between healthy and dead tissue is distinct, especially in green fruits.
- Turnip: Small, water-soaked spots or pitting on the surface. Injured tissues appear tan or gray and give off an objectionable odor.
This article was published by Michigan State University Extension. .