Seeing green through winter's whiteness

Growing root crops and leafy greens during winter’s whiteness could be the ticket to putting a little more green in your pocket over the winter months. However, there is a learning curve to growing a crop in a hoophouse after the snow begins to fall.

“There are unique problems in winter growing situations,” says Zachary Grant, extension educator with the University of Illinois Extension. “Even if you’re a farmer [who has been] growing for decades, if you have never had the experience of growing in a high tunnel in the winter it can be a whole new learning curve in terms of planting dates, how you’re direct seeding or transplanting.” For example, he says irrigation is “totally different,” as is ventilation, the latter of which has to be done more carefully to allow for fresh air exchange while not freezing out your plants.

With that said, growing produce in the winter has the obvious advantage of being able to provide fresh vegetables to markets over the winter.

Growers are using various types of structures to grow crops under cover, including high tunnels and low tunnels. Both are interchangeably referred to as “hoophouses.” Call them what you want, the main point is to consider shape, location and the quality of the covering.

Grant says gothic and gable-style hoophouses are a safer bet in areas that get a lot of snowfall. With Quonset-style hoophouses, the snow will fall down the sides and build up, causing the structure to cave in. This is different from gothic and gable-style hoophouses, where the snow falls off. He says for a walk-in style hoophouse, the sides should be angled at 45 degrees to shed snow. Snow melt can also be an issue.

“Snow load is definitely a potential problem,” Grant says. “You need to clear the perimeter of snow buildup. If you allow snow accumulation on the sides and it melts, you’re dealing with rainwater — you need to have good drainage.”

Locate with winter in mind

Wind can certainly be a factor, but Grant is not worried about winter winds where he’s located, about 30 miles south of Chicago. However, he does stress the importance of locating the structures away from trees and buildings that could shade your crop, especially with the sun at such a low angle in the winter.

“You can put it up in June and say, ‘Hey, no problem,’ but then here you are in the middle of winter and a building or tree could be casting shadows,” Grant says. “You can run into some unique problems in site location and design if you’re not careful.”

Grant suggests growers reach out to their county extension agents for information on how to locate and set up these structures. He says you should also weigh the pros and cons of setting up a large structure yourself or hiring someone to do it for you. Hire someone and it could go up in a day, he says, as opposed to three to four weekends if you’re doing it yourself.

Winter cover

Grant recommends standard greenhouse film or woven fabric to cover any type of winter growing structure. There is also a need for another protective layer inside. He says some growers use another layer of poly inside, however, there can be issues with poly.

“The problem is it doesn’t breathe, and it can heat up pretty quickly,” Grant says. “If you can’t get out there to ventilate, it can cause problems.” He says what a lot of growers are turning to is a 20 percent fabric row cover. He says it works as well as poly in terms of providing protection, but it’s breathable, adding that this fabric is one step up in thickness from the row covers growers use as an insect barrier during the summer months. Too thick of a fabric will inhibit light too much.

“Managing that inner layer is really important,” he says. “If you have a week where the sun doesn’t come out at all it is still critical that you remove that inner layer and allow circulation.”

No rest from the wicked

Just because it’s cold enough outside to numb your hands doesn’t mean there isn’t disease pressure and even weeds inside these structures. Grant says downy mildew on lettuce and spinach can be an issue in a winter hoophouse, and he’s even seen chickweed that had to be plucked. Good ventilation is the key to preventing fungus problems, he says, as are organic-based fungicides.

Feeding the student population

The University of Illinois has a production and learning facility for produce growing and marketing on campus. Matt Turino manages the Sustainable Student Farm at the University of Illinois Urbana-Champaign. The facility consists of three 30-foot-by-96-foot greenhouses run by students, workers and volunteers. Turino says they can produce fresh greens and tomatoes for nine to 10 months out of the year. Winter growing can be a challenge, but it’s worth it as it means fresh produce for students in the dining hall on campus.

“Growing in winter can be significantly more challenging than growing in the season they like to grow,” Turino says. “There is more labor per product, but you can get a better price during winter, and if you’ve got workers you want to keep year-round, it’s a good way to dial in your winter production.”

The farm starts winter greens, including spinach, baby bok choy, baby lettuces and kale in the fall and are able to bring several harvests of the greens into the dining hall over the winter months. Turino says they don’t start greens during the winter months mostly because they don’t have a frost-free water line close to the houses. The winter crop is over in March, at which time they start tomatoes and other spring crops.

“A good place to start is with spinach [because] it’s the most hardy,” Turino says. “It’s a little bit harder to establish, doesn’t compete against weeds as well, but if you can take care of it, it will keep chugging. That and baby kale are the true workhouses.”

Like Grant, Turino emphasizes the importance and challenge of timing winter crops, something that is a little tricky when there still might be summer crops in the greenhouses in late fall or you need to get ready for spring and need to move a winter crop out.

The routine at the farm is to start a different crop in each of the three greenhouses: one in the late fall for winter harvest, one devoted entirely to hardy spinach and one with a mix of greens.

Instead of using organic matter, such as compost that many hoophouse growers use, they rely solely on cover crops to provide nutrients and replenish the soil. Having moveable greenhouses allows this system to work reasonably well.  

“I really like the moveable aspect of the greenhouses,” Turino says. With this method they’re able to start a crop on one side, and plant a cover crop consisting of oats, buckwheat and sorghum sudangrass, on the other. If they can time it right, they’ll sow rye and vetch in the fall for a winter cover. They do this on a yearly basis starting in the late fall. Turino says he thinks being able to move the structures back and forth mainly helps with disease control, but also allows them to flush out salts with rainwater on the uncovered growing plots.

Their biggest challenge to a successful crop, however, is ventilation. It’s finding a balance between controlling moisture buildup and freezing out a crop.

“The big thing is balancing so there is enough air flow for moisture reduction and making sure the plants stay warm enough, which is often counter to each other,” Turnino says. “Putting fans in tunnels helps. Don’t leave anything covered too long — provide good air flow and keep the plants warm.”

Keeping the plants warm and cozy over a long Midwest winter is helping to provide fresh produce to the students at the University of Illinois while teaching the student body how to grow under cover.

Neil is a horticulturist and owner of Green Industry Marketing.