MILLSTON — The marshes of eastern Jackson County — remnants of a prehistoric inland sea called Glacial Lake Wisconsin — are home to one of the state’s most unusual crops. From late spring until late fall, harvest of long-fibered sphagnum moss takes place in Jackson County, the largest producer of the horticulture product in the United States.

“My dad called it ‘Wisconsin’s silent industry,’” said David Epstein, owner of Mosser Lee of Millston, Wisconsin.

Epstein’s grandfather William, his father, Lewis, and uncle Max began the company in 1932. This year the company will ship an estimated 50,000 3.5-cubic-foot bales of moss — worth between $1 million and $2 million — to horticultural businesses all over the country and to Europe. Chile and New Zealand are the two other main producers of long-fibered sphagnum moss; they primarily serve the Asian market.

When the glaciers from the last ice age melted some 14,000 years ago, they left behind swamps and marshland in eastern Jackson County — plus parts of Monroe, Clark and Juneau counties — where long-fibered sphagnum moss grew and flourished. Its ability to retain water at 20 times its weight and its antibacterial qualities were well-known to Native Americans.

The moss also regenerates itself. Marshes are carefully harvested every seven to 10 years. Epstein said his company has never had a marsh go fallow in 85 years. Most of them are on public land and are regulated by the Jackson County Forestry and Parks, which oversees the bidding process that harvesters go through.

Marshes are complicated ecosystems; moss helps sustain them. Mossers rake moss by hand or by machine, breaking it off at the soil line. That allows the perennial plant to continue to propagate through sporing.

Jim Zahasky, Jackson County Forestry director, said the county opened 61 acres of marshes for moss harvesting this year, although the average is about 50 acres. Most bids go to Mosser Lee’s parent company, Deli Inc., and to Hancock Brothers, a family business in nearby Warrens, Wisconsin.

“Once in a while we will have a small producer purchase a marsh that still pulls by hand,” Zahasky said.

Epstein and company president Guy Huus recently took me to a harvest in process at Marsh 50 in the town of City Point, Wis. Dozens of boats — basically flat sleds built with oak — were loaded with moss. The boats are pulled across the marsh by old tractors equipped with wooden tracks that allow them to travel across the spongy surface without damaging the marsh.

Mosser Lee has a custom-built pulling machine that it uses to harvest the moss, but on this day it was in the shop for repairs. But the show goes on, so mossers still have their forks to harvest by hand, which is necessary near the edge of the marsh where the machines can’t reach.

The marsh was surprisingly solid, and my muck boots sank in only a few inches. Underfoot was layer upon layer of decomposed sphagnum moss that had formed peat. Along with the moss the marsh was also thick with wild cranberries, which are separated along with any weeds from the final product.

The loaded boats are emptied on dry land and trucked to the drying plant, which is a large sandy field. Similar to hay, the moss is spread out in windrows, allowed to dry under the hot sun and then taken into a shed, where it is compressed into bales — all done by hand. Huus said the company’s employments peaks at about 40 during harvest season.

In charge of the harvest at Marsh 50 is Mark Zillmer, who has mossed for about 35 years. Zillmer left the businesses for a few years to run a resort in South Dakota but came back when the Great Recession hit.

“This is where I belong,” Zillmer said, sloshing barefoot through the marsh.

While his co-workers wear boots, Zillmer said he quit wearing them a few years ago. Using a fork with curved tines, Zillmer smoothly worked his way through a patch of moss, neatly dropping it on the boat. It’s back-breaking work, especially under the hot summer sun with biting flies. Even with the harvesting machine, it’s still hard to find mossers, Epstein said.

“The best people to hire are from farms, who understand hard work,” he said.

Workers start at about $10 an hour; Epstein said his company usually loses employees to the nearby cranberry industry when its fall harvest begins. About 75 percent of the company’s moss comes from its own workers, but there are still a few individuals who can make $20,000 to $25,000 a year by hand-pulling moss. A proficient hand-puller can do about 100 bales a day.

Epstein said they once mossed marshes owned by the state, but the Wisconsin Department of Natural Resources stopped the practice in the 1990s. He said some of those marshes are now overgrown with invasive weeds and tamarack.

Long-fibered sphagnum moss has been used for bandages and for purifying water, but most of its use today is in the horticulture industry for seed germination, orchid propagation and hanging baskets. Epstein said his moss lines decorative flower baskets in Chicago. Home Depot and Lowes are two of his larger customers.

Epstein said moss is used as a natural scrubber in coal-fired electrical plants, removing mercury emissions. He said it’s also ground up and mixed with iron as a supplement for baby pigs born anemic.

No one can predict the future, but Epstein said business is growing and research continues. We may yet find new uses for a prehistoric product that has grown for millions of years.

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