Greens Extend High-Tunnel Season

10/5/2013 7:00 AM
By Philip Gruber Staff Writer

CHAMBERSBURG, Pa. — Many farmers are harvesting crops right now, but Myron Hess is getting ready to plant.

The Chambersburg farmer is in his second year of planting high-tunnel spinach after his tomatoes are done for the season. “It actually worked out pretty good last year,” he said.

Hess and his family are part of a small trend of growing leafy greens to extend the greenhouse season by several months and reduce the time the structure is sitting idle.

Lettuce and spinach are the most popular crops for late-season growing, and similar crops such as arugula also work, Extension educator Steve Bogash said.

These cool-weather crops tend to bolt and produce seeds too early when they are planted during the summer. In autumn, however, lettuce and spinach can handle temperatures as low as 45 degrees.

Few other greenhouse crops are grown into the winter. “This is a poor time of year for them because they don’t have the light energy” to produce fruit, he said.

The shorter days, cloudy weather and lower sun angle all help to reduce the sunlight that makes it to the plants. Tomatoes that would take 30-35 days to ripen in the summer can take 45-50 days in the late season. A crop is more likely to attract pests the longer it hangs on the vine, Bogash said.

Improvements in LED lighting could make the decreased sunlight less of a factor.

“You’re burning very little electricity” compared with the more common sodium vapor lights, but LEDs are still a new technology and are mostly found in urban greenhouses right now, he said.

Greenhouses are rarely heated, which also shortens the growing season. Heating is a lower barrier to production than sunlight is, Bogash said, because there are fuel sources, such as garbage coal, that can keep costs down.

An ideal greenhouse rotation could feature a spring green planting, a tomato and pepper planting in April and another planting of greens right about now, he said.

Selling late-season greens requires some creativity.

“The auctions really aren’t set well to take greens” because they do not refrigerate crops, Bogash said.

He mentioned one grower who opened up an alternative market for himself by supplying restaurants with his greens twice a week.

“It’s very, very small niche marketing, mainly because the volume is not very high,” he said. “If you can do it, the market is there.”

Dave Miller, farm manager at Miller Plant Farm in York, Pa., is not so sure.

“There is a real market for locally grown lettuce,” he said, partly because of contamination issues with nationally sourced vegetables, especially greens, over the past few years.

Still, until more growers start producing late-season greens, “I don’t know that there’s a market,” Miller said. “It’s not worth our chance to do it on speculation.”

Miller does grow winter greens by order, and he does sow some greenhouse tomatoes in November and December, but his business slows down and closes in January each year.

Hess, the Chambersburg grower in his second year of late-season greens, agreed that cool-season greens are not a cure-all because the greenhouse still sits empty during the early months of the year.

He aims to plant in the first two weeks of October and harvest from mid-November to early January. He could do another planting of greens after that harvest, but that round would run too late and conflict with the planting of tomatoes, which are his main hothouse crop, in February or March.

During the summer, the Hess family sells its produce wholesale and through its retail farm outlet. The winter crops go to a CSA.

Hess grows spinach in both the ground and on raised potting media benches. The two methods produced very similar results last year, he said.

Hess said he does not have to change his practices significantly for the cooler weather, though he thinks custom lighting might improve his late-season production.

“It’s still kind of in the experimental stage,” Hess said of his fall greens growing.

Grace Bender is growing mesclun, a mixture of greens sown together, at her Chambersburg farm this fall. She grows greens all year, along with a variety of other crops, for her farm stand.

Bender said she can barely keep up with the demand for greens in the summer, but this time of year most of her customers are interested in apples and pumpkins.

“It’s interesting how as soon as the melons and the sweet corn are over, they just go to the grocery store,” Bender said. “It’s like they say goodbye, we’ll see you in the spring.’ ”

The customers return around strawberry-picking time the next year.

She figures she could probably grow greens in the winter if she heated her greenhouse. Toward the end of the season, she sometimes needs to wait for the plants to thaw in the morning before cutting. She and a team of women cut individual leaves by hand to ensure customers receive a high-quality product.

Growing fall crops requires only minor adjustments from summer practices, she said.

“Don’t overwater because in the fall we have problems with powdery mildew,” she advised.

Pest management is a little different in the fall, Bogash, the Extension horticulturist, agreed. Powdery mildew, aphids and thrips are all concerns. Aphids in particular like cool weather.

Biocontrol is more difficult in cool weather, said Cathy Thomas, the Pennsylvania Department of Agriculture’s IPM coordinator.

Ladybeetles and purchased parasites are affected by the low light. They are usually introduced around February or March, so October is late in the season for them, she said.

Banded-wing whiteflies and eastern flower thrips may come into greenhouses as food sources outside disappear, but Thomas said they are likely to cause only minor damage.

“They might come in and you might see them, but they won’t attack a crop like a regular greenhouse pest would,” she said.

Even when farmers are not planting fall greens, fall and winter are still busy seasons for greenhouse owners.

John Shenk of Shenk’s Greenhouse in Lancaster does a little cold-weather planting but plans to close the business for the year around mid-October when the chrysanthemums sell out.

He has been potting some ornamentals for next year since August. “The perennials go dormant, and we keep them in a cold greenhouse, so we don’t have to do much with them,” he said.

He heats the greenhouse with oil and liquid propane, and he still has to watch for diseases like botrytis.

The Shenks will spend much of the next few months gathering the seeds, supplies and labels for next year’s crops.

“We’re doing a little transplanting work before (the new year),” he said.

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