Fall 2022

Cover Story

Cranberries frozen into three stacked ice cubes.
Photos by Michael P. King


In early March of 2017, Nicole Hansen found herself kneeling in a cranberry bed, drilling into the soil to check the amount of frost in the ground. She had a tough decision to make.

A multiday heat wave hit in late February, and it melted much of the ice protecting her cranberry vines. Normally at this time of year, the plants would be covered by a one-foot-thick slab of ice, which insulates the vines from extreme cold and biting winds. But much of that ice had disappeared, and a cold front was rolling in. Hansen had to figure out what to do about the exposed vines, which were already carrying the precious buds that would flower and turn into that year’s crop of red, shiny berries.

“When everything melts early, that’s where your biggest risk is. Then you have March and April when, all of a sudden, you’re vulnerable again,” says Hansen, plant health and operations manager at Cranberry Creek Cranberries, a cranberry marsh located near Necedah, Wisconsin. “Then you have to make decisions about flooding.”

For most of the year, it’s clear what growers need to do. Guidelines for the growing season, developed by UW researchers, list low-temperature thresholds at which growers need to take action (i.e., turning on irrigation sprinklers) to protect the delicate flowers and berries. In winter, there’s the thick layer of protective ice over the vines.

However, in late fall and early spring — when growers protect their dormant vines by temporarily covering them in standing water, known as “flooding” — there’s no data-based information about how much cold the vines can handle. This gap didn’t used to be a problem. But things have changed.

“Growers have a system that worked really well for a long period of time. So it’s a fair question to ask: Why are you working on cold hardiness?” explains Amaya Atucha, an associate professor and extension fruit crop production specialist in the Department of Horticulture. “Well, climate change, climate change, climate change. The winters aren’t as consistently cold as they used to be.”

This is the research that growers asked Atucha to do when she first moved to Wisconsin, she says, to help them make better-informed decisions.

Sandy soil sticking to a hanging cranberry.
Sandy soil clings to a cranberry on a plant at the Wisconsin Cranberry Research Station.

Cranberries are native to Wisconsin, which means they’re adapted to survive the state’s harsh winters. But they are still a challenging crop to grow. Commercial operations need to protect and nurture these woody perennial plants to produce an abundant harvest of the gleaming, round, red fruits that consumers expect. In part, this is because cranberry plants are an evergreen shrub — their leaves keep their color and functionality through more than one growing season.

“I don’t know of any other evergreen fruit crop that grows in cold climate; that makes cranberries really special,” says Atucha. “It also makes cold damage a year-round threat, since growers can experience a frost event any time during the season.”

Atucha, a plant physiologist and the Gottschalk Chair for Cranberry Research, started her cold hardiness research with laboratory-based studies, looking at tissue responses to cold. She is now gearing up for field studies, the final steps that will enable her to develop a research-based computer model that growers can consult to make crop protection decisions.

It’s a fortuitous time for Atucha to shift into field research. She will be able to conduct her experiments at the state’s new Wisconsin Cranberry Research Station, a facility near Black River Falls designed to house cutting-edge cranberry field studies.

The station, which started hosting research projects in 2021, is a public/private partnership between the Wisconsin Cranberry Research and Education Foundation (WCREF), the Agricultural Research Service at the U.S. Department of Agriculture (USDA-ARS), and UW–Madison. Its work is supported by an outreach specialist from the UW Division of Extension as well as several Extension funded faculty in CALS, including Atucha.

The facility was built for UW researchers to continue their innovative studies, or even expand their programs, for the benefit of cranberry growers in the state and beyond. It’s a place where growers’ challenges will be addressed and their questions will be answered — including those about cold tolerance.

“In retrospect, we should have flooded [that spring], and we didn’t. So we had injury to the plants,” says Hansen. “Growers need good research about what’s actually happening to the plants from a physiological standpoint and what temperature tolerances they have. We need this information so we can take the actions needed to keep our plants healthy and make sure that our crop potential is being maintained to the highest level.”


Wisconsin is the top cranberry producer in the nation and accounts for more than half of the total U.S. crop each year. It’s also the top-producing region in the world. Yet Wisconsin didn’t have a research station dedicated to cranberries until relatively recently.

“The long and short of it is, our leadership looked at continuing to be a major player in cranberry growing, continuing to be able to pass farms from generation to generation, and being a leader in sustainability,” says Tom Lochner BS’77, director of the Wisconsin State Cranberry Growers Association (WSCGA). “We determined that we needed to develop a research station for cranberries here in Wisconsin, and we needed to up our game on cranberry research.”

The association established a nonprofit, the WCREF, to lead a fundraising effort and administer the station. Growers contributed $750,000 to the project, which included some large in-kind donations in the form of cranberry vines.

“There are [quite a few] research questions that growers want the answers to, and they’re willing to support the station in order to get that work done,” says Lochner, who has shepherded the project through its various stages.

Associate professor Amaya Atucha speaking in a group of field day attendees.
Amaya Atucha, associate professor of horticulture and extension specialist, talks with field day attendees at the Wisconsin Cranberry Research Station.

The new Wisconsin Cranberry Research Station sits on 140 acres of sandy soil in Jackson County, in the heart of the state’s cranberry-producing region. The property has the kind of fine sand that’s perfect for growing cranberries, and it sits alongside Robinson Creek, a picturesque and reliable source of water for the operation. It’s dotted with fresh structures — a research and education building with meeting, lab, and office space; a water control structure on the creek; and a large pollinator garden.

In 2017, the property was purchased from — and, in part, donated by — the Bible family, who grew cranberries for Ocean Spray. Major renovations to the property’s beds took place in 2018, bringing them up to modern industry standards. Vines were planted in the new commercial production beds in 2019 and 2020, and the station now has 27 acres in commercial production.”

Once you plant the vines, it takes two to three years before you get a first crop, and then probably three to five before they get in full production,” Lochner says. “We harvested our first crop off the new plantings last year, and we’re hoping to see the yields improve [this year]. It looks like we should get a good crop.”

Revenue from the crop helps support facility operations, including the work that takes place in the station’s designated research beds. One large research bed hosts thousands of genetically unique plants produced via a plant genetics and plant breeding program.

There’s also a set of four small-scale beds — each just two-fifths of an acre — with individual impermeable membrane liners beneath the beds, making them hydrologically insulated from each other and the surrounding groundwater. These mini-beds are ideal for water quality and quantity studies as well as replicated trials. They are the designated places for research that may involve significant vine damage or crop loss. Before the station was established, all the field research in Wisconsin had been performed on grower-volunteer marshes, limiting some areas of investigation.

“The great thing about the station is that we can do [so many types of experiments], especially things where we know the vines are going to get damaged and there will be less crop, like my flooding studies,” says Atucha. “Or like when a researcher would want to introduce a disease. You’re never going to introduce a disease at a grower’s marsh, but you can potentially do that at the research station.”

The station was built to support the programs run by UW’s fruit team, a group of four cross-disciplinary faculty members with expertise in weeds, entomology, plant pathology, and plant physiology. In recent years, more research power has been added in the form of three new USDA-ARS staff members, focused specifically on cranberries, who have research affiliations with CALS. A fourth hire is in the works.

“I want to understand [how to] treat everything around me the way it should be treated, whether that’s the plant, the soil, the water, everything.”

Nicole Hansen

“Through our partnership with ARS, we advocated for USDA-ARS positions specific to cranberry,” says Lochner. “Now that we have the station, we can start getting more people working on cranberry to build momentum in research and innovation.”

Cranberry grower Nicole Hansen chats with Jed Colquhoun, professor of horticulture, during a field day at the Wisconsin Cranberry Research Station.

There’s a clear theme to the research taking place at the station: sustainability. Projects tend to focus on using less (or better) inputs and sprays and conserving water and energy, all while maintaining or improving fruit yield and quality.

“Research is the key to helping us be sustainable long-term and helping us to understand best management practices and just being good stewards,” says Hansen. “I want to understand [how to] treat everything around me the way it should be treated, whether that’s the plant, the soil, the water, everything.”

This sustainability theme also encompasses Atucha’s cold-hardiness research, which, at its core, is about conserving resources.

“When you have to be flooding, flooding, flooding repeatedly, the amount of water that needs to be moved on the entire property is huge,” explains Atucha. “And the amount of time and energy that is needed to pump that water is huge.”


When water freezes, it forms crystals that grow and grow.

“Those crystals, they’re just like little knives,” explains Atucha. “They can penetrate inside the [plant] tissue, rupturing the entire tissue. Then, when the plant thaws, all the contents inside of those cells leak out, and then the tissue dies because it cannot recover.”

Fortunately, plants have a number of strategies for surviving frigid temperatures, and that’s what Atucha first sought to discover when she launched her cold-hardiness research program. Her research question: How does cranberry protect itself — especially its precious buds — from cold? The goal: to leverage the answer to provide practical guidance for growers. A series of experiments revealed the plant’s approach, a phenomenon called freeze-induced dehydration.

A group of people walking through a field trial, through patches of crops.
Field day attendees walk through a field trial at the Wisconsin Cranberry Research Station. The breeding trial is directed by professor of horticulture Juan Zalapa, right.

“We figured out that those little buds, in order to withstand those really cold temperatures, they dehydrate,” says Atucha. “The less water the tissues have, the lower their freezing point.”

One of the key experiments involved peering inside the plant, and that required the development of a special imaging approach. It was no easy feat, considering the buds of a cranberry plant are smaller than a grain of rice.

“In order to see the freezing events in an intact bud, we needed to use a technology that gives you a different contrast for water and ice. MRI does that,” explains Camilo Villouta PhD’21, who conducted these experiments as a doctoral student in Atucha’s lab. “We found a small animal imaging center in the [UW Carbone Cancer Center]. They had an MRI for rats, with a tiny opening.”

Villouta ended up partnering with the Fab Lab at the Morgridge Institute for Research to develop a novel device that could fit inside the mini-MRI and keep the plant samples frozen without damaging the machine.

“The device needed to have this circulating system [of coolant inside it],” he says. “And everything had to be MRI-friendly. You cannot use metals.”

After a year and a half of iterative tinkering, the team perfected the device and published a technical paper on its fabrication. For Villouta, now a postdoc at Harvard University, it was a lot of fun — and a lot of work.

Group of attendees touring a dam.
Field day attendees tour the rebuilt Robinson Creek Dam at the Wisconsin Cranberry Research Station.

“It had moments of intense effort, because every two months or so we would have an [updated version of the device] to test,” Villouta says. “I had to drive out to the marsh and get vines and then come back to campus and run the samples. It took a whole day. Ultimately, we were able to visualize the liquid water leaving the internal parts of the bud.”

A series of studies funded by the USDA, the Cranberry Institute, Ocean Spray, and the Wisconsin Cranberry Board showed that a plant’s cold hardiness from fall to spring follows a classic U shape. Right after the fall harvest, the plants are very sensitive to the cold. As they dehydrate over the course of the fall, the plants become more and more cold hardy. Come spring, as they begin to rehydrate, the plants slowly turn sensitive again.

This work set the stage for the next big step: a tool for growers. This year, Atucha received a Specialty Crop Block Grant from the USDA to build a cold-hardiness prediction model. It will use local weather data to forecast the cold hardiness of the buds.

“Now, when growers ask me, ‘My ice is gone because it melted [earlier] and it’s going to get cold [again], should I flood or not?’ I can tell them, ‘Well, run the model. With the temperatures that your vines have experienced at the location where you are, run it, and see what the model tells you,'” says Atucha, who was named Researcher of the Year by the WSCGA in 2022, in part for her cold-hardiness work.

The field studies for her new project, which will take place in the replicated research trial beds at the Wisconsin Cranberry Research Station, will test how much cold the plants can take in the late fall and early spring before they need to be protected by flooding — and how long the beds can remain flooded before it causes plant damage.

“This is an example of a project where we really had to start from the basement, building up very basic knowledge about the plants to understand how weather impacts them,” says Atucha. “The model is definitely something that has been a dream of mine, always, because it’s a tool that I can give the growers.”


In addition to being a site for knowledge creation, the Wisconsin Cranberry Research Station will be a place for knowledge sharing. The station started hosting events this spring; and, moving forward, it will be the primary site for many outreach events and trainings for the state’s cranberry growers. Each year, the station will host mini-clinics in the spring, lunch-and-learn webinars during the growing season, and a fall field day — all involving UW researchers. It will also be the place for the annual end-of-season research roundtable, an important gathering to discuss the year’s experimental findings and set new priorities.

Group of attendees walking through a field.
Field day attendees walk through a field trial featuring 3,700 different selections at the Wisconsin Cranberry Research Station.

“After the growing season, we bring in 25 to 30 growers and industry people and all of the research faculty,” explains Lochner. “We sit down and talk about the season and what the researchers are working on. Then we break into small groups and [work on developing] priorities and future directions for the research programs.”

All of these station-hosted events help establish and reinforce the vital two-way relationships between growers and researchers.

“It’s key that UW researchers are in touch with what’s happening with the industry,” says Hansen. “They need to get out into the cranberry beds and engage [with growers] so they can get our input on what we are seeing — the trends and our theories — and utilize that information to set their research priorities.” Even with the station up and running, UW researchers will still be visiting growers on their marshes, notes Atucha. Research needs to be replicated on growers’ marshes as much as possible so the findings represent what’s happening on the state’s commercial operations.

Cranberry Creek Cranberries, notes Hansen, has been hosting 10 or more UW research projects per year in recent years. And she looks forward to the ongoing connections with UW researchers — and how the new station can support the good work being done.

“We’re blessed to have the research crew that we do at UW,” says Hansen. “We have an amazing team there, and I truly appreciate the work that we do together because it does take a team, and it needs to be cooperative. They’re here to help us, and we’re here to help them in whatever way we can to move forward together. That’s the beauty of it, just continuing to work together and now utilizing this wonderful station.”

⊕ Cover Story Sidebar: Beyond Cold-Hardiness Research

The Wisconsin Cranberry Research Station host studies on many aspects of cranberries. Read more.

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