Cranberry Farming

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 got everything except  putting the sand down on the frozen bogs. I certainly learned a lot. Growing, harvesting and shipping of the 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 get some education from the pros themselves.

This is an aerial photos of the Prehn Cranberry farm.

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


As you can see from this graphic, 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, one where the last great glacier, the Wisconsin Glaciation, did not touch, but incredibly surrounded.


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


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

The Wisconsin State Cranberry Growers Association (WSCGA) has a nice description with 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 tart 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. Note that its roots find their home in sandy bogs. The sand is usually acidic, with pH ranging between 4.0 and 5.5. The bog itself is actually a kind of wetland that is not able to support heavy bodies. The bogs usually have a layer of peat at the bottom, which is formed when the dead plants fall to the bottom of the water and sit there over long periods of time. 


Agricultural experts say the soil in Monroe County is of poor quality. What they mean is that the soil is so acidic and the nitrogen in it so low that typical vegetation for farming cannot grow there. But the cranberry vine loves it. The growers work to control the nutrients in the bog as needed.

The vines grow usually less than eight inches high with trailing, thin, wiry stems that bear small evergreen leaves. Flowers appear in late spring. The green leaves might last for about two years, and then fall off. 


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.

Fundamentally, the plants are grown in the beds, each bed surrounded by an irrigation ditch, with built up embankments hosting gravel roads to get around quickly and move equipment to where it is needed. The “Ditch” is man-made and connected to the Lemonweir River, bringing the water supply into the farm. I observed two pumping stations while I was there, though they have more. I have arbitrarily labeled them # 1 and #2. Pump #1 pumps the water from the ditch into the reservoirs, and Pump #2 flows the water into the irrigation systems around a section of beds to feed the plants. 


The Prehn’s had a grass runway airport for small aircraft. I went out to it, walked to the runway, and just looked around, imagining I was in a WWII movie waiting for Memphis Belle to come in!


First on the agenda is the water supply. The water supply to a cranberry farm plays a huge role. There is a considerable amount of bog design and irrigation equipment involved. That said, the water is used in several major ways. 

  • First, you have to have a reliable and ample source of water, 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 the spring and do the same in the fall to protect the fruit. The water is actually warm and protects the plant from freezing even when the air temperature drops below freezing. 
  • Third, it is essential to the harvest, as you’ll see.
  • 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.

Monroe is blessed by plentiful water resources. It contains 11 different watersheds the most significant of which are the Kickapoo, La Crosse, and Lemonweir Rivers, the cranberry bogs, and numerous cold-water trout streams. These watersheds keep the water tables in the area fairly close to the surface, which is good for growing cranberries.


This is a Google Earth shot of the man-made ditch drawing water from the nearby Lemonweir River 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.  

The first point the water in the ditch hits on the Prehn farm is what I am calling Pump Station #1, shown below.

This is she. I wish to point out a few things here. First, note the large pipe in the lower right. She is dumping water back into the river. I believe this reflects how the overall system recirculates the water, a hallmark of many cranberry farms. Second, look at that protrusion at the bottom of the ladder at the station wall. One thing has become increasingly important to cranberry farmers is conservation, so the idea of recirculating as much water as does not evaporate fits that bill.


I took some shots of the machinery in this station for you machinery wonks. My dad would love to have seen this --- a mechanical engineer. My guess is it’s a job to keep all this humming. These pumping stations have to be ready all the time, 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. I should note here that this entire region is a wetland, so you’ll see plenty of marshland. 


It’s kind of weird driving over to this section after seeing all the well designed cranberry beds and supporting irrigation systems. You almost think you have stepped into another world. Such is the nature of marshlands.

Let’s take a look at what I am calling Pump Station #2. This is she. She is taking water from the reservoir and pumping it into another irrigation system that will surround the bogs throughout this large section of the farm.  So we have a good water supply and the farm is in a good wetland ecosystem. 

The next requirement is sand. Plenty of sand. Mega-piles of sand.


As you drive around the cranberry growing regions of the state, you will see large piles of sand. This a typical pile. You will see them all around the region. Remember, the growers are looking for acidic soil with pHs between 4.0-5.5. How does one read pH levels? The pH scale ranges from 0 - 14, with 7 being neutral. The lower the pH the more acidic the soil. 


Water with a pH of 7 is distilled water. Battery acid has a pH level of 0, while household lye has a pH of 14. Lye is often used to reduce the acidity of soil. Vinegar has a pH of 3.  So cranberries like acidity levels a bit on the high side, but not battery acid! Growers are also interested in the levels of phosphate and boron. Cranberries like phosphate as it helps many aspects of growth, especially root growth. Boron is wanted in very small quantities, but 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.

This is a look at a bed at the Prehn Farm with the plants breaking their way through the sand. During bed construction, you might see the growers lay down 4-6 inches of sand. This becomes the planting substrate. A substrate is the material on which the plant grows and obtains its nourishment.


Interestingly, when first setting up these beds, growers will scrape away the overlying topsoil and save it for later. 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. It is important that they level the beds as well as they can with a small crown so water cannot accumulate.


A lot of that excavated soil is used to build up the embankments such as 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 talk about the rest of the irrigation system. Note the corrugated aluminum vertical system component. The bottom line to the entire system is that the water has to flow in and the water has to flow out. The entire exercise is to control the volume, frequency and application rate of irrigation water as efficiently as possible. The water is recycled in the cranberry growth system passing from bog to bog and grower to grower through a series of canals, lines transporting water into the bogs, flume gates, holding ponds, sprinklers, and switches and transformers used exclusively for the pumps.

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


A sprinkler system is employed that uses the pumps, mainlines and laterals with sprinkler heads connected to the feeders from the reservoirs.  The sprinkler system is used during the growing season to replace water lost through evaporation. Most of us 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, but only during the harvest and post-harvest seasons. During the growing season, they look dry like most other crop fields.


The sprinkler system uses the overall irrigation system as its source for water. I have tried to find a good overview of how the irrigation system works, and came up empty. So I’ll have to wing it with some photos I took. 


Earlier I showed you the ditch of water bringing water in from the Lemonweir River, then being pumped into a reservoir, and then being pumped out of the reservoir into the irrigation system.


Cranberry growers have to be able to 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 even if they get hit with an especially hot, dry spell. They’ve got to get enough water to the sprinkler system fast enough so the sprinklers can spray the plants to protect them from the frost. 


Furthermore, they have to be able to clear and drain the bogs with dispatch once the frost threat is gone. 


Here we have a major station. I suspect it has formal nomenclature, but do not know what that is. You see a ditch coming to it. This ditch originated at what I had earlier labeled as Pump #2, which you will recall, is moving water from the reservoir into the irrigation system, in this instance, through this ditch. 


Some are inside the embankment with the bed. This one is located outside the embankment next to a main irrigation ditch. I hope I have not confused you. There are what I refer to as major irrigation ditches getting their water from the reservoirs and located outside the embankments that hold the beds. There are also ditches inside the embankment surrounding the beds. 


Note the corrugated aluminum pieces standing vertically, outside the embankment, and outside the bed of planted crop. I do not know what to call them officially. Also note the small stack of wood on top. They are used to regulate the amount of water that will flow from this ditch into the ditch surrounding the beds. The workers slide the pieces of wood down the front to regulate the height the water must reach in the ditch to flow under the embankment-road to the ditch surrounding the bed on the other side.

This is an example of a similar mechanism on the other side feeding the ditch that surrounds the cranberry bed. Here again, you can see how the wood can be inserted and stacked to the desired height of water in this ditch.

Here you see the wooden slats in there 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 very broad view of the irrigation system. Let’s switch gears and look at the beds and the plants.

It does not matter where you are, when dealing with plants of any kind you have to contend with pests and weeds. I won’t address the pests except to say that they are there and have to be handled. In this photo you see weeds in the midst of the growing cranberry vines. They can be a huge problem for growers, because the vines are low growing 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, of times killing them. There are also chemical approaches. 


Prehn’s beds that I viewed were already planted, so I have not seen how the beds are planted other than through photos. 

I mentioned earlier that the cranberry flower blooms. I took this photo on July 25, and most of the 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, and that is best done by bees. Bees are the main pollinators of cranberry. Pollination is the transfer of pollen grains from the male part off 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 is 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, and perhaps one to three to mature into berries. 


A short story. So there I was at Prehn’s farm in June, a month before the photo of the flower I just showed, and I saw these guys out there with their bees. They had a massive bunch of bees, I can tell you. Of course, being dumb and new to all this, I exited my Jeep and walked over. The guys were yelling at me to get back. I soon found out why. The bees were swarming all around me. I slowly but deliberately returned to my jeep and got in. Incredibly I did not get stung and no bees got in the Jeep, though they were all over it. I quietly drove on! I hate to think what those guys were saying about me!

I wanted to show you this July 25 photo as well. It shows the drainage ditch around the bed inside the embankment with water in it. The crop of berries is really starting to take form.

It’s now October 6, and there has been a remarkable and uplifting change. The fields now have a rusty-reddish hue as the berries turn red.

Remarkable, that Mother Nature. Note the berries are on vines. Magnifico! Having watched the cranberry planting from the beginning, I acknowledge I went whacko over seeing these berries. I then went crazy over the harvest!


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


First things first. Using that irrigation system I described earlier, they flood the bed(s) they want to harvest. The berries have some oxygen in them so they rise to the top, leaving their vines below water.

In goes the harvester. Note the metal planks he uses to get down the embankment and into the bog.  He’s going in front-first.


Let’s take a quick close-up look at this bad-boy. The red horizontal rail on the front will ride on the surface of the water while the yellow hook rails in front will lift up the vines and the attached cranberries almost to a vertical position. Then the blades in back will shake the berries so they fall off their vines. The berries will rise to the top and most of the vines will submerge under the water. This second photo shows him backing in.

So he’s in there and lining up the track he wants to take, after which he lowers his front and rear equipment into 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, I believe called the thrasher. It has shaken the berries off the vines, 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 up the vines in front, and spit out the berries to the rear. The berries rise to the surface while the vines settle down under the water.

The next task is to corral the berries. Here is the yellow boom and the boom operator. The operation here is much like you have seen such booms used to corral oil spills. Except in this operation, the workers get into the bog and pull one end of the boom around the berries while others are raking them into the area being encircled by the boom.

Here most of the berries harvested from this bed have been caught up in the boom. The idea is to locate the corralled berries close to where the next steps are to be taken. I understand these corralled berries are often called a cranberry raft.

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

This is a better look at the washer at work. You see the gray tubing to the right 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.

And a helicopter with cameraman shootin’ the works. It was all great fun.

This is quite an operation to watch. Everyone was busy so I did not ask a lot of questions. But let me see if I can explain what is happening here. Fundamentally, the berries are being pulled up into that large bin on top the yellow apparatus and dumped on to a conveyer belt that in turn dumps the berries into the truck. The part I wish I would have paid more attention to is what is happening with the truck on the left. To address this, I’ll show three photos, first a blow-up of the pipe serving the truck and then two photos from the other side of the truck. It turns out, when the berries are sucked into the bin, a lot of water is sucked in with them. They have to separate the berries from the water.

The berries and water are flowing up the grey tube in the lower left up through the elbow (yellow arrow) and into the bin. But what is that pipe highlighted by the red arrow? The water is being separated from the berries inside that bin. The berries go off to the right onto the conveyor belt, which I’ll show you in a moment, and the water is sent into the pipe marked by the red arrow. 

I took this photo from the other side of the truck you were just looking at. Note the two blue tubes, one on each side, and the water hole in the inside the cranberry raft. 

The water from the truck through the blue tube is “gushing” into the raft. Here is an example of the water being recirculated back into the system.

Let’s return to the berries and the conveyor belt. Up they go. 

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


following the harvest, the growers keep the bogs flooded and wait for the water cover to freeze, 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.