Cranberry Farming in Wisconsin

Wisconsin is number one in the country in cranberries. My friend, and dentist, Dr. Fred Prehn, owns a cranberry operation in Tomah. Fred permitted me to photograph his operation from spring through winter and summer harvest. I viewed it all except for putting the sand down on the frozen bogs. I learned a lot. Growing, harvesting, and shipping cranberries is a big operation. The harvest is arguably the most beautiful. Thanks to Fred and Linda Prehn, along with their super staff, for letting me have free rein of the place and the chance to learn from the pros themselves.

This is an aerial photo of the Prehn Cranberry farm.

Any way you look at it, cranberry farming is a big operation. Prehn’s farm is near Tomah, in east central Monroe County.

Monroe County is the number two producer in the state, behind Wood County. It is well known for its cranberry production. In 2007, total product sales were over $2.8 million from 54 organic farms working 5,432 acres. This was a significant increase over 2002.

Monroe County is located in west central Wisconsin between the Wisconsin and Mississippi Rivers, in a section of the state known as the Driftless Area. It is the area never touched by the last great glacier, the Wisconsin Glaciation.

Cranberry bogs dominate the northeastern portion of the county, where Prehn’s farm is located.

Let’s take a quick look at the character of the cranberry as a plant.

The Wisconsin State Cranberry Growers Association (WSCGA) has an excellent description and an easy-to-understand graphic. The WSCGA describes the plant like this:

“Cranberries grow on low-trailing vines in sandy or peat marshes, but in Wisconsin, cranberry marshes are flooded with water to aid in harvesting. Because the tiny berries contain a pocket of air when the marsh is flooded, the berries float to the surface to be picked up by harvesting equipment.”

The plant, often referred to by growers as a vine, is a perennial. Its roots find their home in sandy bogs. The sand is usually acidic, with pH ranging between 4.0 and 5.5. The bog is a kind of wetland that cannot support heavy bodies. The bogs typically have a layer of peat at the bottom, formed when the dead plants fall to the bottom of the water and sit there over long periods.

Monroe County’s land is not suitable for most agriculture. Typical vegetation for farming cannot grow there because the land is so acidic and the nitrogen is so low. The cranberry vine loves it. The cranberry growers work to control the nutrients in the bog as needed.

The vines usually grow less than eight inches high with trailing, thin, wiry stems that bear small evergreen leaves. Flowers appear in late spring.

Let’s get started on the cranberry season at Prehn’s Farm. First, a broad overview of things you’ll see as we press ahead.

The plants are grown in the beds. An irrigation ditch surrounds each bed. Built-up embankments are above the beds and ditches. Gravel roads enable people and equipment to get around quickly.

In the case of the Prehn Farm, the “Ditch” connects to the Lemonweir River and brings the water supply to the farm. I observed two pumping stations there, though they have more. I have arbitrarily labeled them # 1 and #2.

Pump #1 pumps the water from the ditch into large water reservoirs. Pump #2 sends the water from the reservoir to the irrigation ditch systems. Those systems can then feed water to the beds and the plants.

Water supply is first on the agenda. It plays a huge role. There is a considerable amount of bog design and irrigation equipment involved. Water is used in several significant ways.

  • First, you must have a reliable and ample water source, a way to circulate it around the farm, and an ability to store it for later use.
  • Second, the water is a source of frost protection to shield the fragile flower blossoms from frost in Wisconsin’s unpredictable spring and do the same in the fall to protect the fruit. The warm water protects the plant from freezing even when the air temperature drops below freezing.
  • Third, as you'll see, water is essential to the harvest.
  • Finally, it is essential following the harvest during the winter, when it covers the bogs, freezes over to protect the beds, and then is covered with sand. When the ice starts melting in spring, the sand falls to the bottom and serves as a nutrition source for the vines.

Plentiful water resources bless Monroe. The county hosts 11 different watersheds, the most significant of which are the Kickapoo, La Crosse, Lemonweir Rivers, and numerous cold-water trout streams. These watersheds keep the water tables in the area reasonably close to the surface, which is suitable for growing cranberries.

This is a Google Earth shot of the artificial ditch drawing water from the nearby Lemonweir River. This photo shows the water entering the northeast portion of the farm.

The Lemonweir River, a tributary of the Wisconsin River, finds her source near Wyeville, just to the northeast of the farm.  It is part of the Central Wisconsin River Basin watershed. 

This is what I am calling Pump Station #1. It is the first point at which the water in the ditch enters Prehn's farm. The pump then drives the water from the river into a reservoir. The large pipe in the lower right and the protrusion at the bottom of the ladder at the station wall enable the growers to recirculate water back to the river.

This photo gives you a closer look at Pump #1.

These photos give you a closer look at the equipment. These pumps must be well maintained.  The grower’s team must keep the pumps humming. The pumping stations must always be ready, especially as climate conditions change quickly.

You’re now looking beyond this pumping station. Those bodies of water are parts of the reservoir.

Here are some shots of the reservoir areas. This entire region is a wetland, so you’ll see plenty of marshland should you visit this area.

Let’s look at what I call Pump Station #2. It takes water from the reservoir and pumps it into an irrigation system that feeds the cranberry bogs. 

The next requirement is sand. Plenty of sand. Here you see large piles of sand. As you drive around the cranberry-growing regions of the state, you will see large piles of sand—this is a typical pile.

The growers are looking for acidic soil with a pH between 4.0-5.5. The pH scale ranges from 0 - 14. Seven is neutral—the lower the pH, the more acidic the soil.

The ideal pH for cranberries is 4.2-5.5, which is quite acidic compared to other crops.

Growers are also interested in the levels of phosphate and boron. Cranberries like phosphate. It helps many aspects of growth, especially root growth. Boron is desired in very small quantities. It is needed for pollination.

The growers are constantly adding nutrients of various sorts to the beds throughout the season to achieve the balance they want.

Here you see the plants breaking their way through the sand. You might see the growers lay down 4-6 inches of sand during bed construction. This forms the planting substrate. The plant grows and is nourished by the substrate material.

Growers will scrape away the overlying topsoil and save it for later when first setting up these beds. They might excavate the subsoil to about 18 inches above the water table and form rectangular beds, perhaps 150 ft. wide by 600 ft. or more long. They must level the beds a with a small crown so water cannot accumulate.

Much of that excavated soil is used to build up embankments like the one you see here. It is also used for dikes and other water control structures. It is useful for installing gravel roads to create irrigation ditches such as you see to the side of this bed, and it will eventually hold the water when the beds are filled for harvest.

This is a good time to discuss the rest of the irrigation system. Note the corrugated aluminum vertical system component. The system is designed to enable water to flow in and flow out. The growers seek to control irrigation water's volume, frequency, and application rate as efficiently as possible. The water passes from bog to bog and grower to grower through a series of canals, water lines, flume gates, holding ponds, sprinklers, and switches.

All cranberry bogs I have seen in Wisconsin have sprinkler systems. They are installed before the vines are planted. Keep in mind that Cranberries do not grow in standing water.

A sprinkler system uses the pumps, mainlines, and laterals with sprinkler heads connected to the reservoir feeders.  The sprinkler system is used during the growing season to replace water lost through evaporation.

You might have seen photos of the beds flooded. Such photos are the most common ones used to describe cranberry farming. However, the beds are not flooded during the growing season. They are flooded only during the harvest and post-harvest seasons. I will show you that later. During the growing season, they look dry like most other crop fields.

The sprinkler system uses the overall irrigation system as its source of water. Cranberry growers must move large amounts of water to the sprinkler systems, often with very short notice. That is especially true when frost is still a threat or if they get hit with a scorching, dry spell.

Recall that Pump #2 moves water from the reservoir into the irrigation system through ditches. Some ditches, like this one, are outside the embankment. 

Others are inside the embankment surrounding the beds.  Note the corrugated aluminum pieces standing vertically. Also, note the small stack of wood on top. They regulate the amount of water that will flow into the ditch.

The workers slide the pieces of wood down the front to regulate the water flow. Here you see the wooden slats are at a very high level. I took this shot in October when the beds were being flooded for harvest. But I wanted you to get an idea of how the water system can be controlled with these fairly rudimentary pieces of equipment.

Well, that’s a rookie’s broad view of the irrigation system. Let’s switch gears and look at the beds and the plants.

When dealing with plants, you have to contend with pests and weeds. In this photo, you see weeds amid the growing cranberry vines. They can be a huge problem for growers because the vines grow low while the weeds pop up higher, steal water and nutrients, and hide some of the vines from the sun. Downstream they can get tangled up in the harvesting equipment as well. One trick is to cut them back so the cranberry vines can create a kind of low-growing “jungle canopy” over them and deny them sunlight, oft times killing them. There are also chemical approaches.

I mentioned earlier that the cranberry flower blooms. I took this photo on July 25. Most flowers were gone. I should have been there earlier in the spring. This is the best shot I have. You can see the berries have already taken form. Had I gotten there earlier, you would have seen that the flowers resemble the head of a Sandhill crane, or so they say. In any event, that’s how the cranberry got its name!

The cranberry fruit does not simply grow on its own. It requires pollination. Bees are the primary pollinators of cranberry. Pollination is the transfer of pollen grains from the male part of the flower (anthers) to the female part (the stigma). Both the anther and stigma are contained in the same flower. The bees move the pollen from the anthers in one flower to the stigma in another. Four pollen grains stuck together are known as a tetrad. A cranberry flower needs at least two tetrads to set fruit, while eight or more tetrads per flower will lead to the largest berries.

It is worth noting that most of the flowers do not produce berries. A vine “upright” might hold two to seven flowers. Perhaps one to three matures into berries.

This photo shows the drainage ditch around the bed inside the embankment with water in it.

I zoomed in on that photo. The crop of berries is starting to take form.

It’s now October 6, and a remarkable and uplifting change has occurred. The fields now have a rusty-reddish hue as the berries turn red. Mother Nature is amazing.

It turned out that October 6 was the day the workers were in the harvest. This is arguably the best part. Fred Prehn made it quite a day, inviting the press and anyone interested. We even had helicopter coverage!

The workers flood the bed(s) they want to harvest using the irrigation system I described earlier; the berries have some oxygen in them, so they rise to the top, leaving their vines below water. The harvester goes in, down the embankment, and into the bog.  He’s going in front-first.

The red horizontal rail on the front rides on the water's surface. The yellow hook rails in front lift the vines and the attached cranberries almost to a vertical position. Then the blades in the back shake the berries, so they fall off their vines. The berries will rise to the top, and most vines will submerge under the water.

Here you see the forward mechanism pushing her way through the flooded bog, cranberries attached to their vines and mostly below water. The berries you see on the surface have already been shaken off their vines from an earlier track through.

Now you see the rear mechanism, called the thrasher. It has shaken the berries off the vine. The berries pop to the surface and are ready for the next step.

As you can see, it almost looks like he’s laying carpet. Lift the vines in front, and spit out the berries to the rear. The berries rise to the surface while the vines settle under water.

The next task is to corral the berries. This is the yellow boom and the boom operator. The booms are frequently used to corral oil spills.

In this operation, the workers get into the bog and pull one end of the boom around the berries while others rake them into the area encircled by the boom.

Most of the berries harvested from this bed have been caught up in the boom. I understand these corralled berries are often called cranberry rafts.

A truck pulled up alongside a cranberry raft, and a system is applied to wash the berries and suck them into a tube that will take them to a loading truck. A worker moves the cranberries along.

Note the gray tubing to the right. It is carrying the berries upward. Oh good, help is on her way. This is one of the news broadcasters there to tape the event and interview—the workers and owner.

A helicopter came along with a cameraman to film the events below. It was all great fun.

This is quite an operation to watch. Everyone was busy, so I did not ask a lot of questions. The berries are being pulled up into that large bin on top of the yellow apparatus. They are then dumped onto a conveyer belt that dumps the berries into a truck standing to the right.

The berries and water flow up the grey tube in the lower left through the elbow (yellow arrow) and into the large bin. The system separates the water from the berries. The berries go off to the right onto the conveyor belt, which I’ll show you in a moment. The water is sent into the pipe marked by the red arrow.

The water is then sent back into the bed. I took this photo from the other side of the truck you were looking at. Note the blue tube passing the water back into the cranberry raft.

The water recirculates back into the raft. It conserves the water and freshens it up through recirculation. After the berries are separated, they go up the conveyor belt and into a truck standing by.

Once the truck is loaded up, it departs for the distribution point. Another car pulls up, and work continues.

Following the harvest, the growers keep the bogs flooded and wait for the water cover to freeze hard enough to hold heavy equipment laden with sand.

The growers then cover the ice with sand.

When the ice starts to melt in the spring, the sand will sink to the bottom and refresh the nutrients in the substrate.