Frost, Freeze and Green Tomatoes

 

From Franklin County, PA Master Gardener Facebook Notes (October 2013)

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 VS. FREEZE

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.

FROST

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.

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.

Covering plants before the sun sets may be protection from frost as this can help retain heat near the plants.

 FREEZE

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

We are closing in on the first average frost. (Check the date for your area.) Since it takes about six weeks for a tomato to go from flower blossom to ripe fruit, you should have pruned or pinched back your tomato plants in early-to-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.

Kansas State also suggests roasting them for eating warm or cold, using in side dishes or freezing in small batches to use throughout the winter.

HARVEST AND STORE TO RIPEN

Pick and store your mature green tomatoes and let them ripen up on counter top or windowsill but not in the refrigerator. 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.”

Kansas State Extension Master Gardeners note that "not all green tomatoes will ripen off the vine. They must have reached a "mature green stage." Look for full-sized tomatoes with a white, star-shaped zone on the bottom end of the green fruit. Also, on maturing green tomatoes, skin at the blossom end may be beginning to change color from green to pink or red." Use immature green tomatoes in recipes such as salsas or fried.

Ron 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.

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.

CKagan, Master Gardener

**********

Interested in herbs? Looking for Gardening Gifts?

 Check out the Herb Sampler  description on this Blog  

SPECIAL Price reduction on Amazon here

The Second Edition Herb Sampler (2019) is available through Amazon.