PHOTO: Danielle Scott/Flickr
Frank Hyman
September 25, 2018

Think of oyster mushrooms as the first step for farmers who want to cultivate fungi for fun and profit. Prices for oysters (Pleurotus ostreatus) remain around $10 to $12 a pound at farmers markets because of interest from chefs and home cooks.

In nature, oyster mushrooms grow on dead and dying trees in the woods, so you could spend a lot of time searching to find enough to sell. But with the right production system, a farmer could grow as much as a ton of oyster mushrooms every year in a few hundred square feet of indoor space: That could be as much as $20,000 a year at retail prices once everything is running smoothly.

You needn’t fill your space with dead trees to grow them either. Oysters are easy to grow on almost any cheap, available plant waste: peanut hulls, cottonseed hulls, sawdust and wheat straw. Mycologist Tradd Cotter, author of Organic Mushroom Farming and Mycoremediation (2014), even grows them on spent coffee grounds, cardboard and tattered cotton blue jeans, on his Mushroom Mountain farm in Easley, South Carolina.


Get Growing

I learned the ease of growing oysters by filling a 5-gallon bucket with spent coffee grounds in our kitchen. By sprinkling a bit of mushroom spawn—you can start your own or buy the spawn online—as I added coffee grounds, I created a miniature garden of growing mushrooms. I merely left the bucket lid ajar for ventilation and let a little light in. It took less than a month to harvest a couple of pounds of mushrooms without leaving the house or doing anything that resembled work.

Making coffee essentially pasteurizes the grounds with wet heat—an important first step in mushroom cultivation. When organic matter is wet, it becomes an attractive food source for any fungi spores floating in the air.

By using wet heat to pasteurize your mushroom’s food source—also called substrate—you give your chosen mushroom spawn a head start in the race to colonize your coffee grounds or other materials.

To grow a marketable quantity of oyster mushrooms, you can use more readily available materials either from your own farm or from local agricultural processors. A commonly used substrate is wheat straw, and you might want to begin your education with that. Even if you don’t grow grains, you can easily buy bales of straw. Be sure to shred the straw into shorter bits. A string trimmer can do the job if you drop some straw into a big garbage can and insert the trimmer like a kitchen mixer whipping up some batter.

“Oyster mushrooms are some of the fastest-fruiting fungi on the planet, making them perfect for educational projects and disaster relief,” Tradd writes in his ’shroom book.

Tradd shares additional techniques for growing various mushrooms on wood chips, logs, stumps, sawdust and, yes, even fresh coffee grounds and old blue jeans. One chapter covers suitable fast-acting classroom projects for school children.

oyster mushrooms
wendellsmith/Flickr

Mushroom Musts

The key things when growing oysters are:

  1. Start with a pasteurized substrate to give your spawn a head start.
  2. Inoculate the substrate with good, fresh mushroom spawn immediately after the substrate has cooled to keep out weed fungi.
  3. Maintain a growing environment of fresh air, appropriate humidity, optimal temperature and indirect light (as found in the woods).
  4. Use an opaque container. Oyster mushrooms will start to fruit wherever they are exposed to light. In a transparent container, such as a clear plastic bag, tiny mushrooms will start to fruit over every square inch of the bag. They will be too diffuse and too tiny to be worth harvesting. In an opaque container, mushrooms will fruit only through openings that allow light to enter.
  5. Use a container with the optimal amount of openings so that you get the optimal number and size of mushrooms sprouting. For example, if growing in a sausage-shaped plastic bag big enough to produce 10 pounds of mushrooms, cutting only one hole would probably yield one 10-pound mushroom too large to sell. But 50 holes would yield too many tiny mushrooms and could dry out the substrate. But eight holes would probably yield an equal number of clumps, each a little over a pound in weight—the perfect size for market.
  6. Harvest at maturity, as the curled-down edges of the caps start to flatten out.

You can pasteurize your substrate with several low-tech methods described by Tradd in his book, such as using solar heat or even a solution of wood ash that can pasteurize at room temperature. Tradd prefers pasteurizing a batch of wheat straw by dunking it into 55-gallon, food-grade metal drums with tight-fitting lids. He stands his drums on bricks or cinderblocks to make room for a propane burner and then heats the drums to about 170 degrees F for one to two hours. That’s enough time to pasteurize the straw.

The wet straw is heavy, so Tradd uses an electric hoist and a simple aluminum cage to raise and lower each batch of straw in and out of the drum. A winch on a vehicle or a set of pulleys—and a set of muscles—will work in place of an electric hoist.

Final Prep

After adequate heating, the straw is dumped out onto a stainless steel table wiped down with rubbing alcohol to eliminate weed fungi.

Once the substrate has cooled enough to handle, Tradd puts it in his containers, which might be long plastic bags, poly tubing, PVC pipes or even repurposed nursery pots soaked in a 1:10 solution of bleach to water to eliminate weed fungi. When two-thirds full of substrate, the nursery pots are easy to stack. The drainage holes make perfect escape hatches for the mature stalks of oyster mushrooms.

Some species can be grown outdoors on fresh logs and stumps with assistance from overhead sprinklers during dry spells. Find best results growing them in enclosed structures that let you manage humidity and temperature. This is especially true for oyster mushrooms from tropical regions; these include pink, golden and Florida oysters. But even temperate varieties such as king, tree, blue and phoenix produce more under controlled conditions. Some farmers even adjust the oxygen and carbon dioxide levels indoors to a small degree to promote growth and fruiting.

The time from inoculation of the substrate with spawn to harvest might be three to five weeks. Later flushes should arrive several weeks apart. Harvest singles or clusters by hand, twisting them to remove the base of the stalk. Trim the end to keep your harvest clean; you can also use the trimmed ends to start another batch of spawn. Arrange the mushrooms facing the same way in boxes to save space, reduce damage and to make them look more appealing.

You can store them in a refrigerator for one to two weeks. Given their flavor and the demands of the market, I bet they won’t stick around that long.

This story originally appeared in the March/April 2018 issue of Hobby Farms.

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