Too Cool for Tomatoes

How to optimize the sweetness of your tomatoes.

October 22, 2013

Q. I planted my tomatoes in a new bed last year, and although I got a good crop, they were not sweet at all (except for the ‘Sun Gold’ fruits). I have planted these heirloom varieties before with good results. Was it the steer manure and compost I added to my clay soil or the cool summer we had this past year?

Cynthia Vena
Portland, Oregon

A. While fertility plays a role in tomato success or failure, the fact that your plants yielded well points to weather as the culprit. Sunshine and warmth both are critical to sugar development in tomatoes. Excessive soil moisture also limits tomatoes’ sweetness—watering deeply once or twice a week is preferable to frequent, shallow watering.

“It was so cool and cloudy last summer,” says Leslie Pohl, former director of Portland Community Gardens. “The ground didn’t warm. Even container tomatoes did poorly.”

“The Portland area can have spotty weather for tomato ripening, and early varieties are generally recommended,” says Weston Miller of the Community and Urban Horticulture Faculty at Oregon State University in Corvallis. “‘Early Girl’, ‘Stupice’, ‘Siletz’, and ‘Oregon Spring’ are among my favorites. Midseason-ripening tomatoes such as ‘Willamette’, as well as cherry tomatoes, are also good choices.”

“Be patient and hold off planting until soil temperatures warm up—usually after Memorial Day,” he says. Plastic mulches to warm the soil can also help provide more favorable conditions for tomatoes. For later varieties (including most heirlooms), a coldframe or greenhouse can improve the chances for a successful harvest.

Originally published in Organic Gardening Magazine, April/May 2012