CORVALLIS, Ore. – Autumn frosts can turn your green tomatoes that are still on the vine to mush. But, if you pick them before frosts or heavy rain hit them, many will ripen off the vine.
"You can tell when a tomato is nearing maturity by its light green, almost translucent, appearance," said Barb Fick, horticulturist with the Oregon State University Extension Service in Benton County. "Tomatoes that are not in this 'mature green' stage won't ripen."
A green tomato is mature if its interior is yellowish and the tissues are gelatinous, or sticky, when the tomato is cut, Fick said. "Mature green tomatoes also have a pink or reddish tinge on the blossom end," she said.
To check for maturity, cut 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.
To store and ripen mature green tomatoes, put them in deep straw, wrap them individually in newspaper, 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. Storage temperature should range from 60 to 70 degrees. They will ripen over a period of three to four weeks.
"Tomatoes will ripen satisfactorily in the dark," Fick said. "Sunlight is not needed, but the temperature is important."