The Greeks and Romans were fond of eating mushrooms collected in meadows and woods but it was not until about 1650, in Paris, that one particular species, the White Mushroom (Agaricus bisporus), was actually domesticated, or cultivated. (Other species had been cultivated in China many years earlier.) These cultivated mushrooms thrived on horse manure, but not that of other animals. About 1800, Parisians found that mushrooms could be grown in the dark, in the subterranean stone quarries that honeycombed their city, which provided even temperature year round. Mushroom cultivation did not reach the United States until 1865. Kennett Square, near Philadelphia, was an early leader.
At St. Paul, Minnesota, mushroom farming lasted a century, from the 1880s to the 1980s. Mushroom Valley was the informal name for a stretch of the Mississippi River gorge in downtown St. Paul, containing about 50 caves, originally dug in the St Peter Sandstone for sand, but later mostly used for mushroom growing.
In the early days it was often necessary to abandon a cave after growing mushrooms in it for just a few years due to the accumulation of diseases and insects. About 1890, however, a method for the germination of mushroom spores was developed at the Pasteur Institute in France. A pure spawn industry evolved, providing disease-free inoculum, grown in milk bottles, to mushroom farmers.
An article in the St. Paul Pioneer Press, May 27, 1923, titled “St. Paul’s Caves Eclipse Backlot for Gardening, Except for Crop Foes,” by Jay W. Ludden, offers us a unique glimpse of mushroom pathology at the St. Paul caves. Ludden was clearly awed by the sheer size of St. Paul’s mushroom caves: “These caverns have cathedral-like arches, and looking into them through the dusk that conceals details and accentuates the big lines, one is reminded of etchings of the interiors of medieval temples. This impression is strengthened when at the distant end of the cave the workmen’s lamps give light as from an altar.”
“As with all gardening,” Ludden mused, “the more one goes into it, the more one is disillusioned as regards its simplicity. Pests and blights and molds confront one, and remedies are more or less difficult to apply.” By 1923, the pure spawn technique had been adopted by local growers: “Spawn culture is a big industry of one St. Paul company, which has had at one time on the racks used for the purpose, 125,000 milk bottles containing spawn.”
But Ludden reported that “Terrific battles are carried on in the dark depths of the caverns, victory going sometimes to the gardeners, and again to the bugs, which, microscopically, are appalling and ferocious.” The newspaper article contains an incredible image, reproduced here, showing a man, dagger drawn, battling an enormous manure fly inside a cave carpeted with the “ghostly blossoms” of mushrooms. “The artist has depicted a terrific battle between a mushroom grower and one of the enemies that attack his crop,” the caption explains.
One of the standard authorities on mushroom pests, USDA Circular 457, published in 1941, describes the manure fly (Aphiochaeta albidihalteris) as having “a hump-backed appearance. They are quite active, moving about constantly in a series of jerky runs.” While there were several control measures, such as light traps, dusts, and fumigation, the best strategy was to prevent infestation of beds in the first place. Horse manure compost was placed in the caves, allowed to “pasteurize”—also called “sweating out”—during which the temperature of the compost spontaneously rose to 145 degrees Fahrenheit, which killed or drove off most of the pests. After letting the temperature return to normal, the beds were inoculated with spawn, and the mushrooms began to grow.
The adult flies themselves did not attack the mushrooms. Instead, the maggots, if pasteurization failed to kill them, ate the spawn and tunneled into the stems and caps. And the manure fly was not the only kind of fly attacking the crop. While manure flies (“little flies”) were the first to appear, they were replaced later in the growing cycle by fungus gnats (“big flies”).
Ludden listed other mushroom pests according to their scientific names—often badly misspelled. “Mites, wood lice, springtails” are included. Springtails are tiny wingless insects, but they sometimes covered the floor of the cave in such great numbers as to resemble gunpowder. Also mentioned are fungal diseases of mushrooms, such as damping-off, and a “spottiness” that may be due to mold. Just as significant is that other devastating mushroom diseases of the day, such as “bubbles” and “mummy,” are not mentioned by Ludden, so perhaps they were not important at St. Paul.
Another of the “crop foes” not found was weeds—at least those of the photosynthetic kind. “For the weeds grow to a height of only four or five inches,” Ludden continued mawkishly, “pale and frail, like the heroines in the old time volumes of Select Reading for Young Ladies, then droop and die, like one of those heroines distraught by the idea that her mother suspects her of having told her first untruth.”
Further technological changes after 1923 improved the lot of the mushroom grower. The adoption of the “tray system” in the 1930s, and the consequent disappearance of the old floor beds, was a big step forward in controlling mushroom pests. No longer could the pests seek refuge in the underlying soil during pasteurization, only to later reinfest the beds. Indeed, remains of these wooden trays form the chief diagnostic artifact of former mushroom caves at the present time.
A more recent newspaper article, “Mushroom Farming is Family Tradition,” in the St. Paul Pioneer Press, March 28, 1976, paints a portrait of Mushroom Valley in its final days. “Mushroom growing,” the farmers pointed out, “remains hard and backbreaking work because some things simply cannot be mechanized—including the picking of mushrooms.” Few members of the younger generation seemed willing to adopt the manure-based lifestyle involved. By contrast, Lehmann, the “Mushroom King,” had already moved his operation to “the world-renowned cement-block caves of Lake Elmo” in 1965. Specially designed aboveground facilities like the latter, while initially more expensive than caves, allowed for much finer tuning of environmental conditions, including the control of pests and diseases.
Excerpted from SUBTERRANEAN TWIN CITIES.