Too cold, too hot, too bad for tomatoes

  • Article by: MARY JANE SMETANKA , Star Tribune
  • Updated: August 8, 2011 - 9:17 AM

The fickle summer weather has left many tomatoes green and rock-hard.

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Photo: Mary Jane Smetanka, Star Tribune

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This is what gardeners dream of in January.

On a steamy Friday afternoon, Dowling Community Garden in south Minneapolis smells of dill and onions. Beans climb, bugs buzz, birds sing. The rainbow stems of Swiss chard shine as brightly as the hollyhocks and zinnias, and someone is already composting overripe squash.

But many of the lovingly caged tomatoes -- warty heirlooms, tiny cherries and perfectly round hybrids -- barely show a blush on their green skins.

It's been a rough year for tomatoes, the most precious prize of a Minnesota garden. Gardeners have been venting about rock-hard, green tomatoes -- in August! -- at National Night Out parties, at work and in online garden groups.

Julie Weisenhorn, state director of Minnesota's Master Gardener Program, understands the frustration.

"We suffer all winter with those things that taste like nothing," she said. "To grow a really awesome tomato in Minnesota, what could be better."

While some tomatoes seem to be doing OK -- a few plants at Dowling had bright red fruit at their base -- gardeners have complained that this year, tomatoes just don't look right. They're lanky, with sparse foliage and fruit. And what's there is very late to ripen.

Vince Fritz, a University of Minnesota horticultural science professor at the Southern Research and Outreach Center in Waseca, says gardeners can blame Mother Nature and perhaps themselves.

Early in the growing season, it was cold, rainy and dark. Tomatoes don't like that. "One thing that happens then is that plants that like sun tend to get leggy," Fritz said.

Then the weather flipped to searing. Tomatoes don't like that, either. The plants drop their flowers when temperatures soar above 90 degrees, reducing yield.

Fritz recommends that gardeners prune tomato plants when they're small. He likes to have plants with just two leaders, or main branches.

"You need to do pruning early in the season with tomatoes," he said. "Remove all those side shoots. Pruning hastens fruit set and ripening."

Tomatoes like regular watering, but Fritz said they should not be fertilized now. Fertilizer contains nitrogen that promotes leafy growth, not fruit. To hasten ripening, Fritz suggests cutting off new flowers and, on plants that bear large tomatoes, taking an especially painful step: nipping off green fruit that's the size of a quarter or smaller.

"The chances of those ripening are close to zero," he said.

Tomatoes aren't the only vegetables suffering. Fritz said pea yields are down by 50 to 60 percent because seed simply didn't sprout in cold, sodden soils. Sweet corn is affected, too, in certain areas.

But squash seems to be doing well. Chard, eggplant and herbs like basil are loving the heat and the rain, Weisenhorn said. Her strawberries are flowering again, she said, "and my raspberries are kicking butt. The blueberries are too."

She is bracing for the State Fair, where the master gardeners answer questions from fairgoers. The most-asked about topics?

Apples, raspberries, turf -- and tomatoes.

Mary Jane Smetanka • 612-673-7380

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