Sure, you probably buy mushrooms at the grocery store, but have you ever wondered how mushrooms grow? Get ready to take a trip to a bustling farm that defies traditional farm rhythms of sunshine, rainfall and wide-open spaces.

Shrouded in darkness, this farm lies primarily under roof, within the confines of a stark concrete warehouse that sprawls across seven acres. The “fields” are thousands of trays in neat rows on concrete slabs. There are no seasonal chores since farmers plant a new crop every other day and harvest all year-round. And here, fungus is actually a good thing.

Mushroom Farming

From Farm to Grocery Store

Despite its cave-like environment, the Monterey Mushrooms farm is a model of agricultural productivity, trucking out more than 600,000 pounds of mushrooms every week to grocers and food suppliers throughout the Southeast.

Located in East Tennessee, it is one of 11 farms operated by Monterey Mushrooms, a California-based grower with farms in the United States, Canada and Mexico. The Loudon plant, built in 1977 by Ralston Purina, eventually became part of Monterey Mushrooms. This farm’s 550 workers grow primarily white buttons along with some portabellas.

“Although we are producing an agricultural product, I see our operation more as a manufacturing facility, or more specifically, a food plant,” says Greg Sweet, general manager. “The majority of our operation takes place indoors, allowing us to control most of the growing variables. We focus more on growing what we can sell when we can sell it – versus selling what we grow.”

National mushroom sales are stable and solid. According to the National Agricultural Statistics Service, U.S. growers sold 817 million pounds at an average of $1.17 per pound from their 2008-2009 crop. The vast majority of mushroom farms are in Pennsylvania and California. However, farms like this one scattered across the rest of the country in strategic marketing areas.

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how mushrooms grow

Meet a Mushroom Farmer

Bob Moore, a veteran mushroom farmer who worked in Colorado and Pennsylvania, moved to Tennessee in 1981. As quality assurance manager for the Loudon farm, he helps oversee the operation.

“This isn’t a cave, but it might as well be,” Moore says of his workplace. “There are no windows, and when you’re here, you don’t know what time of day it is. You just focus on your job. Every day is the same, but every day is different, too.”

It’s the chemistry behind the finicky mushroom that makes each day unique. The mushroom is a fungus. Because it does not have chlorophyll, it is not a green plant and cannot use energy from the sun. Instead, it extracts its carbohydrates and proteins from a nutrient-rich food base. Thus, the first phase of the farm operation is making compost.

“Good compost is the key ingredient in producing a successful mushroom crop,” Sweet says. “Some growers say compost contributes as much as 80 percent to the overall production process.”

The composting takes place on the five acres outside the warehouse. The process involves bringing in tractor-trailer loads of stable bedding from Kentucky Thoroughbred farms and mixing it with wheat straw from Tennessee, chicken litter and nitrogen-rich urea. During the 22-day process, temperatures within the piles reach up to 180 degrees and spark chemical changes that transform the compost into a food source for the mushroom.

The compost “food source” is mixed with vegetable oil and water and poured into wooden trays that are 6 feet long, 4 feet wide and 8 inches deep. After a pasteurization process kills any pests present in the compost, these trays become the “gardens” where farmers plant mushroom seeds, or spawn. (Mushroom seeds are actually rye seed inoculated with the mold of a strain of mushrooms.)

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Mushrooms growing at Kitchen Pride Mushrooms in Gonzales, TexasHow Mushrooms Grow

To grow mushrooms, farmers try to create the same conditions that occasionally cause mushrooms to spring forth in your front yard in the spring and fall.

Covered with a layer of peat moss, limestone and water, the trays go from room to room – each with carefully controlled temperatures and humidity levels – as they support the crop for 31 days from planting to picking. As the ammonia level drops and the compost’s odor turns from musty to sweet, the spawn fuzzes and turns into “pins,” which eventually form “buttons.”

“A mushroom is ready when the stem starts to elongate and get thinner and the cap starts to flatten out,” says Moore. “They’re picked before the veil opens between the cap and the stem. Our pickers are trained to recognize this. We’re after about seven pounds of mushrooms per square foot of tray, and we have 1,100 trays per crop.”

“It’s very tough work,” says David Beyer, associate professor of plant pathology at Pennsylvania State University. “Growing mushrooms is 24/7 and takes a lot of attention to details. I’m impressed by the team effort in Loudon. It’s not unique to the industry, but it’s certainly a class act.”

Want to know more about mushrooms? Find mushroom selection, storage and cleaning tips here.


  1. My wife and I operate a small native plant nursery in northwest Alabama. We also operate a landscape installation company. We are interested in mushroom compost in bulk. Can you provide information to us?


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