Oyster Mushrooms

Growing Oyster Mushrooms alongside Vegetables: CRAFT United Piedmont Tour at Granite Springs Farm

On Sunday, Sept. 29th the Collaborative Alliance for Farmer Training (CRAFT), United Piedmont met at Granite Springs Farm in Pittsboro to learn from farmer Meredith Leight about growing oyster mushrooms.

Granite Springs Farm started in 2010 and currently run a 40 member CSA and sell the vegetables, eggs, and mushrooms that they grow at the Pittsboro Farmers Market, Chatham Mills Farmers Market, and several local restaurants, including a UNC sorority.

Folks came from all over the greater triangle area for the tour and potluck event – from Pittsboro, Durham, Raleigh, Hillsborough, Silk Hope, Carrboro, Chapel Hill, and some from as far away as Fayetteville! The crowd included new and beginning farmers, established farmers, farm interns, local restaurateurs, a horticultural therapist, and even folks looking to start their own farm-based non-profits or other growing businesses.  Some grew shiitake mushrooms, but wanted to learn about oyster mushroom. A few were interested in incorporating mushroom growing into their aquaponics operations.

Mushroom Beginnings

Granite Springs started growing oyster mushrooms with an $8000 grant from the Rural Advancement Foundation International (RAFI)’s Tobacco Communities Reinvestment Fund, which gives money to projects that are replicable by other farmers and focused in areas that have been adversely affected by the demise of the tobacco industry.  Granite Springs wanted to fit mushroom production into their existing vegetable operation. Their goal for the grant is to grow mushrooms in an already-existing farm building, making adjustments as needed to retrofit the space for mushrooms, and to stretch towards year-round production.

And indeed –that’s what the farm is doing. The mushrooms grow in cylindrical black plastic bags that hang from ceiling poles in their hoop house and greenhouse (Oyster mushrooms require an enclosed growing space due to pest problems – there’s a particular beetle that loves to chow down and infest them).



The farmers first learned about growing mushrooms from Tradd Cotter through a workshop at Mushroom Mountain. He’s also giving a pre-conference talk at the Carolina Farm Stewardship Association’s Sustainable Agriculture Conference this November if you’re interested in learning more from the experts first-hand!  Meredith also recommended the book Growing Gourmet and Medicinal Mushrooms by Paul Stamets as a helpful resource.

She buys spawn from Mushroom Mountain as well – they clone wild spawn found growing locally that are well adapted to our climate. Part of the challenge in growing mushrooms is that each strain prefers different temperatures at different stages of development, but can generally tolerate from 50-90 degrees Fahrenheit. To keep the mushrooms cool enough in the summer, Granite Springs’ hoop houses have screens and sides that roll up to let in cooler air and they also regularly mist the growing mushrooms. .

In terms of light, mushrooms like 10-12 hours of exposure, so when the days get shorter they use florescent lights to substitute. Elongated stems and “funky” caps are usually signs of not enough light or of too much carbon dioxide.

Mushroom Production Processes

Mushrooms need a substrate material to grow on – and Granite Springs uses a mix of wheat straw, cotton seed hulls, and wheat bran. While oyster mushrooms are some of the easiest to grow and will grow on many waste-stream mediums, the carbon-nitrogen ratio in the substrate material is important.

The first step is to prep the substrate – shredding it small enough to pack very densely into the growing bags, and mixing the different materials together in the correct ratio. They first put the substrate into a welded basket – because then the substrate must be pasteurized to create as clean a slate as possible for the mushrooms to grow on.

Meredith explains the pasteurization process

Granite Springs pasteurizes their substrate in 55 gallon barrels filled 2/3 of the way full with water that has been heated to 170 degrees using propane tanks . They lower the substrate into the heated water, weigh the substrate down so it doesn’t float to the top, and then let it cook for two hours. The same water can be used for two batches but then needs to be replaced with fresh. .

But the process isn’t done yet – then they spread the substrate out on a sanitized tarp to let it cool and inoculate the substrate with the mushroom spawn by mixing it in with a rake before stuffing it into the big (5 to 6 feet tall) cylindrical plastic bags that the mushrooms will grow in.

Granite Springs is primarily a vegetable grower who is growing mushrooms to supplement their other crops. They usually dedicate 1 day a week to stuffing these bags and using this process they can stuff about 8 bags a day.

There are many ways to do this process, and Granite Springs is constantly tweaking it as they go. For example, other mushroom producers like Growing Power use lime to pasteurize the substrate instead of hot water.

For each batch of mushrooms they stuff in the grow bags, Meredith also creates a small, clear plastic “test bag” so that they can monitor how the mycelium is growing, whether it’s getting moldy, etc. Each bag is labeled with the type of mushroom, the date the bag was filled, and a batch letter.

Finally, they hang the bags and poke holes in them for the mushrooms to grow out of and to allow oxygen in. This process is best done in as sanitary an environment as possible – or in the environment they’ll be growing in – as the bags suck in air when the holes are punched.

The mycelium “run” throughout the bag until it is fully colonized, eating the substrate for nutrients. Then, when the bag is fully colonized, the mycelium realizes they need to replicate – or die! Good old evolutionary survival instincts at work. That’s when they begin fruiting – sending out super strong mushroom fruits through holes in the bags

Harvesting and Storage

The mushrooms need to be misted each day throughout the growing process to keep moist up until right before harvesting. If they are wet when they are harvested the mushrooms can turn to mush, so the timing of the misting schedule is very important

The mushrooms should be harvested before they start to drop their spores (you’ll be able to tell because they change shape). A warning: when mushrooms release their spores into the air, it can be harmful for those with asthma or other lung issues – so it’s important to set up careful air exchanges in growing spaces, as well.

Harvesting usually involves just pulling and twisting the mushroom lightly, but some are stronger than others: Meredith recounted a tale of a time when she pulled with all her might and couldn’t get the mushroom stem to break off!

After harvesting, the mushrooms should then ideally be stored at 35 degrees. Meredith uses a CoolBot, which overrides an AC system allowing it to maintain a cooler temperature (actually usually 39-40 degrees) without freezing over.

Granite Springs stores the mushrooms in labeled paper bags and will keep 4-5 days before sale – but fresh is best, which is why mushrooms are a great local product to sell to local restaurants! The quality will be much better than anything shipped in from the Northwest.  You can also store the mushrooms in cardboard boxes covered with film and with holes punched in them – they need to breathe and not gather moisture, so they don’t like wax boxes!

After harvest, the spent substrate can be composted!  The already once waste-stream material can become yet again useful in another cycle. Granite Springs will soon be borrowing the vermicomposter from Piedmont Biofarm and is determining the best ratio of green matter needed to compliment the straw material.

Marketing  Mushrooms

Why grow mushrooms? In addition to being super tasty, the economics are great for farmers. According to Meredith, it costs about $15 per column to grow, and each column yields about 10 lbs of mushrooms. Meredith then sells the mushrooms at $12/lb (blue oyster) and $16/lb (gold, pin, and phoenix oysters). She sells between 35 and 40 pints of mushroom per week.

At markets, she’ll bring a grill and offer samples for customers – and with one taste, they’re hooked. Then she’ll launch into the nutritional and health benefits of mushrooms. Did you know oyster mushrooms are colon and breast cancer tumor inhibitors? They’re also high in Vitamin C, are a great non-animal source of Vitamin D,  can lower cholesterol, and contain two times the amount of protein as an egg by weight. Oyster mushrooms are also amazing filters. They can break down toxins and clean up a multitude of petroleum spills through a process called mycoremediation.

Looking into the Future

Granite Springs Farm is also in the process of starting an intentional agrarian community on their land.  They’re holding open meetings every 3rd Monday of the month with a potluck and discussion topic if you’re interested in learning more!

They also hold many workshops and other events on the farm – check out their website or Facebook page to stay in the loop!

You can register now for the next CRAFT United Piedmont tour happening October 20th at Everlaughter Farm in Hillsborough. The special topic will be tool-sharing and fall/winter season extension!