Iowa’s unseasonably cool nights this August may be perfect for sleeping, but temperatures are among the factors that play a role in our gardens.
I’ve heard from several gardeners whose tomatoes are slow to ripen this year, and Linn County Master Gardeners who take calls at the “Hortline” for Iowa State University Extension, are hearing the same.
“We’ve had numerous calls about tomatoes,” said Linn County Master Gardener, Devon Dietz. “I think this cool weather hasn’t helped it a lot.”
Dietz attributed the still-green tomatoes to a combination of factors: the wet June, followed by a dry July and August, along with nights with temperatures in the low 60s, 50s and even 40s.
“We had so much rain in June, they got used to a lot of water and it just kind of turned off,” he said. Normally, tomatoes thrive when temperatures are in the 80s during the day, with 70s at night, Dietz added.
Those conditions have similarly affected vine crops, he said, such as zucchini.
Dietz said calls also have been coming in regarding leaves of tomato plants that are yellowing and falling off, usually from the bottom of the plant, on up.
That condition can be attributed to soil-borne pathogens, particularly when tomato plants have not been mulched. Dietz recommended using straw or dried grass clippings to mulch the plants (best to let the clippings dry a few days, especially from treated lawns.)
Also, remember to rotate your tomatoes, so they are not planted in the same area more than once every three years. This gives those pathogens less opportunity to build up in the soil, he said.
The same is true for tomatoes grown in containers. Dietz advised changing the soil in the planters every year.
What to do about those green tomatoes, especially in case of an early frost?
The tomatoes can be harvested green, before the frost, and will gradually ripen indoors. Dietz said recommendations call for individually wrapping the tomatoes in newspaper, though I’ve had luck just placing them in flats on the countertop.
If you have other gardening-related questions, the Hortline takes calls from 9 a.m. to noon and 1-4 p.m., Monday through Thursday, and Fridays, from 9 a.m. to noon, at (319) 447-0647.