Indoor Oyster Mushrooms: Big Yield, Small Spaces

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Grow pounds of oyster mushrooms right in your home with fairly little effort and just a small amount of space. All you need is 16 square feet, a few plastic buckets, an organic material to the grow the mushrooms on, like spent coffee grounds, and some spawn. Use recycled or salvaged items and this hobby becomes a low cost investment that produces delicious returns you can eat and share with friends.

In the following excerpt from Organic Mushroom Farming and Mycoremediation, mycologist and author Tradd Cotter shares his plan for a 4×4 indoor growing system. Also from Cotter’s book, learn how to grow mushrooms on your jeans, seriously!


Urban Mushroom Cultivation

No forest? No spare garage? With a little creativity, mushrooms are easier to grow in tight places than you might think. You can grow a substantial amount of mushrooms by incorporating them into community or rooftop gardens, or even by growing them indoors in closets and spare bathrooms. Of course, the amount and type of space you might have can vary considerably. The key is to evaluate your situation—with a site analysis or, if you are indoors, a walk-through—and choose the methods that will help you maximize yields for your given situation.

Indoor Small-Space Cultivation

The most common and efficient mushrooms for fruiting indoors in small spaces are oyster mushrooms (Pleurotus spp.). You’ll be surprised by how little space they take up. You can pasteurize small batches of growing medium (or substrate, which is another word for the energy source or food that mushrooms require) on your stovetop. You do not need a humidified room; an extra bathroom or closet works fine as long as you provide a simple humidity tent over the fruiting cultures, so that the primordia don’t dry out and abort.

You can house as many as thirty 5-pound bags of inoculated fruiting substrate—enough to produce 8 to 10 pounds of oyster mushrooms a week—on a five-tiered rack placed near a window, which typically takes up about 6 square feet of floor space and rises to a height of about 6 feet (which coincidentally is very close to the size of a small closet, if you have an extra one you would like to devote to fruiting). Or you can cultivate them in buckets on spent coffee grounds. Wherever and however you grow in your small space, if you’re indoors be sure to provide ventilation to allow for gas exchange, add a fluorescent light if your setup isn’t near a window, and cover the rack or containers with a humidity tent. (I would line the floor and walls with plastic if you are experiencing excessive moisture buildup. The object is to provide extra humidity to the mushrooms, but you also need to protect your structure from excess water to avoid rot.)

The 4×4 Indoor System

This 4×4 system will require about two hours of work per week to maintain, but the returns are worth the effort. You can locate your containers in a closet, spare bedroom, or bathroom, or even outside during warmer months. The system is scalable depending on the container size. I call for 5-gallon buckets here, but you could also use pails from a local restaurant or stacking plastic bins in the 5- to 13-gallon range. Just pick a size that is appropriate to the space you have available and that you can easily fill with the amount of growing medium you can prepare on your stovetop. Oyster mushrooms fruit about three weeks after spawning and can flush at least three times over the course of thirteen weeks, so to keep your operation going consistently, you’ll use as many as fifteen containers. (A flush is a periodic fruiting cycle of mushrooms.) Drill 1/2-inch holes evenly spaced around the sides, about every 6 to 8 inches. Make sure all the containers have secure lids and can be stacked several units high without any danger of tipping.

To begin, procure your growing medium. This can be spent coffee grounds or any kind of pasteurized (or partly sterilized) agricultural by-products, such as grasses and cereal straws. To pasteurize a substrate, heat a large pot of water, three-quarters full, to a near boil, then add dried plant debris such as shredded garden plants, chopped cereal straw, plant-based kitty litter, or any other organic material that can be used to grow oyster mushrooms. Push the floating medium down to submerge it, heating for one to two hours on low heat with the pot covered. Remove from the heat, drain all the water, and allow the medium to cool completely. You may have to pasteurize two separate batches to have enough substrate to fill the container completely; if you want to make it a onetime cooking event and you don’t mind having a smaller harvest, just use smaller containers, such as 2-gallon buckets. If you are having a hard time finding growing media for oyster mushrooms, try pet or livestock feed stores to see if they have any bulk shredded straw pellets (such as the Streufex type); or you can buy bags of wood pellets (for use in pellet stoves). Both shredded straw and fuel pellets are good for oyster mushroom substrate when you mix them with a little shredded alfalfa (from a pet supply store) as a nitrogen supplement.

Mix the growing medium with your spawn. You can do this right in your growing container, but to make things easier I generally mix the substrate and spawn in a larger tub and then transfer the mixture to the growing container. Fill the container, and then label it with the date, the substrate, and the type of spawn you used. (Keep a log and record what you are doing if you wish to improve your yields.) Snap the lid onto the spawned container, and move it to your growing space. Keep all your newly spawned containers under a loose layer of plastic; this forms both the humidity tent and the fruiting chamber.

Once you have a series of containers under way, you can organize them by the order in which you expect them to fruit. Oyster mushrooms will generally pin (begin forming mushrooms) in three weeks. Keep the pinning buckets in the front and any resting or colonizing buckets in the back. Once the mushrooms flush and you harvest them, you can rearrange the containers to position the buckets that will fruit next in the front. If you want to stagger the harvest, once the mushrooms are producing and harvested, let some of the buckets rest and dry out a little, which means pulling them out of the humidity tent and reducing misting for at least two weeks, then return them to the humidity tent and resume misting and watering.

The second flush will typically produce half the weight of the first, and the third will produce half of the second (5 pounds, 2.5 pounds, and 1.25 pounds, for example), so if you are making a container a week, all of the containers will have overlapping flushes producing different amounts. Weigh and add up the yields of each flush every week to see if you are producing too much or too little for your goals.

For calculating yields, after the first thirteen-week cycle, when your system is up and running and you have mushrooms in all stages of cultivation, I would use a starting estimate of 1.75 pounds of oyster mushrooms for every gallon of substrate you prepare every week. So my 5-gallon-bucket system should average 8.75 pounds a week.

The up-front costs for this system would probably run about $170: $65 for buckets, $10 for a shallow tub in which to mix the growing medium with the spawn, $20 for the growing medium, and $75 for three bags of spawn. Of course, it will be cheaper if you use secondhand or salvaged items. During your first thirteen-week cycle you will basically be paying off the cost of any purchased materials, but the return on your investment will only get better after that. Thereafter, your costs for every thirteen-week cycle will be for the spawn and the growing medium (approximately $95, or $7.31 per week).

Given potential yields of 8.75 pounds per week and a value of $10 per pound, this production system can be a good investment. Aside from preparing the growing medium and filling the weekly container, the only maintenance it needs will be to rotate the containers once a week, to mist frequently, and to harvest the wonderful, protein-rich mushrooms—enough for a family of four to enjoy year-round. What is amazing is that this entire system takes up only about a 4-foot by 4-foot space, or 16 square feet, but it can be scaled to produce as many mushrooms as you, your family, and your neighbors can use. And after the buckets are finished fruiting, you can add composting red wiggler worms to produce soil that can be used to grow greens and other vegetables on sunny balconies and rooftops!

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