BLACK RIVER FALLS — Season-extending structures can make a big difference for farmers growing market produce, and some options that come without an intimidating start-up cost are available, according to UW-Extension Horticulture Specialist Julie Dawson.

Structures like caterpillar tunnels, hoop houses and greenhouses can be used to extend summer growing season for heat-loving crops like tomatoes and cucumbers or to grow cold-hardy crops deeper into the winter or through the winter, Dawson said during the 2020 Fresh Market Growers educational meeting put on in February by Jackson County UW-Extension. Speakers at the meeting discussed several topics for beginning market growers, including marketing with social media, merchandising for fresh market sales and greenhouse production.

The structures allow growers to control water and humidity through irrigation and ventilation, temperature passively through the structure or actively by adding heat, and light through the use of shade cloth for some plants.

“When you’re building a season-extending structure, you’re trying to manipulate a microclimate so it’s better for your plants,” she said.

Dawson said the concepts behind season-extending structures are far from new. Small-scale farmers in Paris in the late 1800 were feeding the entire city and exporting to England producing throughout the winter in a climate that is slightly warmer than Wisconsin’s but farther north, leading to less winter daylight.

“They were able to be self-sufficient year-round,” she said. “This changed with the switch to the automobile from the horse because the horse manure was a primary source of fertility and heat in the off-season.

“A lot of this has been done before and it is possible despite feeling like we are in a very cold climate.”

Dawson said there are several factors growers must consider when deciding what type of structure is best for their farm.

Caterpillar tunnels — low structures that typically allow a user to stand up only in the middle — come at a lower cost to construct than a high tunnel, Dawson said. They are also relatively mobile, allowing crop rotation from year to year.

High tunnels, with enough structure and bracing, can also be designed to be mobile, she said.

“Mobility is something to really think about if you are putting in a new structure,” Dawson said. “It can save you a lot of headaches with the end of the honeymoon period and you start to see disease issues and soil issues.

“You don’t have as many options if you can’t move the tunnel.”

Greenhouses can get more expensive to build and are quite often heated or cooled. Dawson said some hoop houses can also be heated, but they aren’t as well insulated as greenhouses so efficiency drops.

“You can get really fancy with greenhouses really fast,” Dawson said. “On the scale that most direct-market growers are working on, you probably don’t want to get too fancy unless you have a good market for winter produce and want the possibility of giving it some heat.”

Dawson said site selection is also a key consideration for growers thinking about a structure. She recommended considering orientation relative to prevailing wind and sun as well as ease of access for watering and snow removal purposes.

“You’re going to have to baby-sit some of these structures quite a bit,” Dawson said. “If it’s off in a corner somewhere, it’s easy to forget or not be able to get to.”