Wednesday, October 2, 2013

Frost, Freeze and Green Tomatoes

by Carol Kagan, Franklin County Master Gardeners
Frost on the Pumpkin (WKTY-TV, Lexington, KY)
We are fast approaching the last frost free date of October 15 in Franklin County and many home gardeners, eager to either have homegrown tomatoes for Thanksgiving or loath to discard any possible foodstuff, are looking at their green tomatoes.

Frost, “killing frost,” freeze warnings, a “killing freeze” - what is the difference? In casual conversation the terms frost and freeze are often interchangeable but there is a very real difference. Frost and freeze are two distinct phenomena. These terms take on significance when they are associated with the growing season.
North Carolina State

According to the National Oceanic and Atmospheric Administration (NOAA), frost is the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth's surface and earthbound objects falls below 32°F. A frost advisory is issued when widespread frost formation is expected over an extensive area. Surface temperatures are usually in the mid-30’s. If a frost period is sufficiently severe to end the growing season (or delay its beginning), it is commonly referred to as a "killing frost."

 Dr. Katharine B. Perry, North Carolina Extension Service, has compared frost and freeze conditions for protection of horticultural crops noting frost and freeze protection methods are based on preventing or replacing radiant heat loss.
Frost on Lettuce- Gary Bachman, Mississippi State University

Because frost is primarily an event that occurs as the result of radiational cooling  - heat loss at night - it frequently occurs with a thermometer temperature in the mid-30’s. A radiation frost happens when a clear sky and calm winds (less than 5 mph) allow an inversion to develop. An inversion occurs when the heat radiating from the earth rises and causes the cooler air above to be pushed down, and temperatures near the surface drop below freezing.
North Carolina State University
Covering plants before the sun sets may be protection from frost as this can help retain heat near the plants.
Frost damaged tomatoes, squash and peppers-
Gordon Johnson, Kent County, Delaware
According to NOAA, a freeze is when the surface air temperature is expected to be 32° F or below over a widespread area for a significant period of time. Use of the term is usually restricted to advective situations or to occasions when wind or other conditions prevent frost.

Dr. Perry explains than an advective, or windborne, freeze occurs when a cold air mass moves into an area bringing freezing temperatures. Wind speeds are usually above 5 mph and clouds may be present. Attempts to protect plants are very limited under these conditions.

 A "killing freeze" may be used during the growing season when the temperature is expected to be low enough for a sufficient duration to kill all but the hardiest herbaceous crops.

According to NOAA, freeze warning are issued during the growing season when surface temperatures are expected to drop below freezing over a large area for an extended period of time, regardless whether or not frost develops.
Green tomatoes - Carol Kagan

Tomato Flower-Carol Kagan
We are less than two weeks away from the first average frost. Since it takes about six weeks for a tomato to go from flower blossom to ripe fruit, you should have pruned back your tomato plants in mid-September (cutting the growing tip off all the vines and any new blossoms to redirect the plant’s energy toward ripening up the existing fruit).

Oops! Okay, you were enjoying the weather and forgot. Now what?
There's always fried green tomatoes or you can store them to ripen up later.

Pan-Fried Green Tomatoes (From PS WPSU Local Food Journey)

   2 large green tomatoes       1/4 cup bread crumbs
   1 egg salt                            1/4 cup milk black pepper
   1/2 cup all-purpose flour    Peanut oil for frying
   1/4 cup cornmeal

Directions: Slice the tomatoes 1/4- to 1/2-inch thick.

Whisk together the egg and milk. Place the flour and a little salt and pepper into another bowl. In a third bowl combine the cornmeal, bread crumbs, salt, and pepper.

Bread the tomatoes by first dusting them with flour, then dipping them into the egg, and finally coating with the bread crumb mixture. *

Heat the oil (1-2 cups) in a large sauté pan over medium heat. Cook until the tomatoes are golden brown on both sides. Drain on paper towels.

* An online blog (Tadpole's Outdoor Blog) suggests that these can be put in a single layer, frozen and then stored in a plastic bag in the freezer to use later. Perhaps fried green tomatoes for Christmas!
Tadpole's Outdoor Blog

Pick and store your green tomatoes and let them ripen up. Ron Wolford, University of Illinois Extension horticulturist, notes that green tomatoes can be harvested before a predicted frost.

“You can tell when a tomato is nearing maturity by its light green, almost translucent, appearance,” according to Barb Fick, horticulturist with the Oregon State University Extension Service. “Tomatoes that are not in this 'mature green' stage won't ripen.”

Fick notes that a green tomato is mature if its interior is yellowish and the tissues are gelatinous, or sticky, when the tomato is cut. Mature green tomatoes also have a pink or reddish tinge on the blossom end.
Check for maturity by cutting a green tomato in half. If the pulp filling the compartments is jelly-like, it is mature green. In immature green tomatoes, seeds are easily cut through and the jelly-like pulp has not yet developed.

Checking maturity in green tomatoes - Courtesy of
Wolford recommends removing the stems, washing and drying the fruit. Wrap each tomato in newspaper and place them in a single layer on a shelf or in a box. You can also put them in deep straw or just lay them in a box so that they are not touching. Check tomatoes every few days and discard any that show signs of rot.
Wrap tomatoes in newspaper - Carol O'Meara,
Colorado State Univ. Extension Service
Tomatoes will ripen satisfactorily in the dark, according to Fick, and sunlight is not needed; however, temperature is important. Storage temperature should range from 60 to 70 degrees. They will ripen over a period of three to four weeks.
Picking and storing the mature green tomatoes in mid-October means there's a good chance you can have some tasty, home-grown tomatoes for the Thanksgiving celebration.

For more information, check these links:

Cornell Cooperative Extension, Chemung County: Understanding Frost

Mississippi State University: Winter’s frost, freeze can damage landscape

Penn State WPSU Local Food Journey: Field Notes and A Recipe for Pan-Fried Green Tomatoes

PSU Preserving Your Harvest - Tomatoes

Colorado State University Extension Service: Ripening that Huge Crop of Green Tomatoes (Carl Wilson, Colo. State Coop Extension Agent)

Cornell Cooperative Extension, Chemung County: Guidelines for Harvesting Vegetables
Compiled by Eric de Long

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