By Will Broussard
(From left to right) North Spore mushrooms grown in containers by @allisfarm, @withcarrington, and @lindsey.l.jones
Here at North Spore, we are no strangers to container growing. In fact, North Spore actually began as an urban mushroom farm that grew 100% of its mushrooms in buckets! We were able to scale the process from making 5-10 buckets per week to making hundreds of them, enough to service dozens of restaurants and multiple farmer’s markets! Mushrooms can be grown in all shapes and sizes of containers on a range of dead or decaying organic materials such as livestock manure, straw, wood chips and even coffee grounds.
In this article we’ll focus on two methods of container growing: oyster mushrooms cultivated on straw in buckets using a high pH water bath (just like North Spore used to do!), and heat treating wood chips to grow a wider range of mushrooms in other types of containers. Keep in mind that different sizes and shapes of containers can be used for both of these methods. We chose to focus on buckets because they are easily sourced, can be stacked, and are what North Spore used for years. Feel free to experiment using different types of containers!
The bucket tek, or technique, is one of the most reliable methods to grow oyster mushrooms quickly and on a predictable schedule. It’s sustainable, beginner friendly, and easy to scale up - to a point. We’ll teach you how to source and prepare buckets, pasteurize your substrate, inoculate, and incubate your buckets with mushroom spawn. Finally, we’ll cover how to best harvest your edible mushrooms. We’ll be following North Spore’s tried and true recipe which helped us scale up from a couple buckets at home to a commercial mushroom farm.
What You Will Need
- 5-gallon bucket with lid or other type of sealed plastic container
- drill with ½” bit
- chopped straw
- leaf mulcher, or straw shredder (if not using pre-chopped straw)
- large plastic tote, trash bin, or intermediate bulk container (IBC) for commercial scale
- cinder block or other weight
- mushroom spawn (either sawdust or grain)
- pH meter
- hydrated lime (calcium hydroxide)
- 10-lb mesh onion bags
- rubber gloves
- opaque trash bag or stealth grow tent
Step 1: Select and Prepare Bucket
A brand new 5-gallon bucket with lid can be purchased at your local hardware store or for free from a local business such as a restaurant or food processor, where products are often shipped in food grade 5-gallon buckets and discarded thereafter. Inspect and clean your bucket thoroughly to reduce the chance of contamination during the colonization and fruiting process. Using a ½” drill bit, drill holes in a diamond pattern around the full circumference of your bucket. This drill bit creates holes large enough for the mushrooms to fruit from but not big enough to let the substrate dry out while it is colonizing.
Step 2: Select and Pasturize Substrate
Fungi like to feed on dead or decaying organic material and will readily grow on a variety of commercially available substrates including manure, straw, sawdust, wood pellets and even coffee grounds. Straw works great for oyster mushrooms; it is inexpensive and easily purchased from farm supply and home improvement stores. For easier colonization, shred or chop the straw using a leaf mulcher or lawn mower. Some garden centers will also sell pre-chopped straw which is usually more expensive, but allows you to skip the chopping step in the process. To give the mushrooms the advantage over rival molds and bacteria, you’ll need to pasteurize the straw to kill off any contamination.
There are a variety of ways to do this, but we’ll stick to what North Spore did in the early days and use a cold-water pasteurization with hydrated lime. Begin by filling a large plastic tote, clean trash bin, or intermediate bulk container (IBC) with tap water. Once filled, slowly add the hydrated lime to the water to increase its pH from near neutral to 12.5. Use a large spoon or paddle for stirring the water, and continually check the pH with a pH meter to measure the water as you add the lime. When the water and lime mixture reaches 12.5 pH it is ready to pasteurize your straw. Separately, fill a few 10-lb onion sacks with the chopped straw and weigh each on a scale. Take note of the average weight of each of your bags filled with dry chopped straw.
Straw being cold soaked with hydrated lime
This will be useful later in the process for determining the moisture content of your straw. The use of onion bags facilitates submersion while also making it much easier to determine the end moisture content of the mushroom substrate prior to inoculation. Once the desired pH is reached, submerge the onion bags, and use a cinder block to keep them below the water. They should remain submerged overnight, for at least 12 hours to complete the pasteurization process.
Step 3: Remove and Drain Substrate, Determine Moisture Content
Straw drip drying
Allow the substrate to soak overnight or longer so that it can get sufficiently hydrated and pasteurized. Remove the bags from the water and place them somewhere to drip dry for another 12 to 24 hours. If indoors, a simple frame made from 2x4s with hooks and a drip tray will suffice. Oyster mushrooms like their substrates to have a moisture level of at least 50%. If the substrate is too wet you are likely to get anaerobic bacteria growth, but if it is too dry the mushrooms won’t grow well. Once the scale reads twice the dry weight you have reached a good moisture level and it's time for inoculation.
Step 4: Add Spawn to Substrate
Inoculating your bucket involves simply combining your substrate with grain or sawdust spawn. The amount of spawn you should add to your substrate to maximize yield is known as the spawn rate, and a single, 5-pound bag of grain or sawdust spawn for each 5-gallon bucket chopped straw is more than sufficient. You can get away with 2.5 pounds of spawn for each bucket if you wish. There is a direct relationship between the spawn rate and the speed and reliability of colonization.
It is best for beginners to err on the side of too much spawn instead of too little! Before filling your buckets be sure to sanitize them with 70% isopropyl or by dunking them in water treated with a little bleach. Combine your spawn and straw manually on a sanitized tabletop or by building up alternating layers of substrate and spawn in a bucket until the bucket is full. If creating alternating layers, use 1.5 inches of straw followed by a thin layer of spawn.
Note: If you have any leftover spawned straw that would be insufficient for filling an additional bucket, try experimenting and putting it into a smaller alternative container like a tupperware bin, milk carton, or tin-can (we’ve even seen old bird cages filled with inoculated straw!) You’re likely to get another healthy flush of mushrooms. It’s a great excuse to experiment!
Spawn and hydrated straw being mixed
Step 5: Let Bucket Colonize in a Cool, Dark Place
Once the bucket is inoculated, cap it, and place it out of direct sunlight, preferably somewhere cool (between 30 – 75 degrees F) such as a basement or cool garage. Pink oysters require colonization temperatures above 60 degrees F while some cold tolerant blue oysters prefer temperatures closer to freezing. Confirm the specific requirements for your particular mushroom spawn. During the colonization process, it is important that the bucket doesn’t dry out. An easy way to avoid this is to drape a trash bag over the bucket while it’s colonizing or place the bucket in a stealth grow tent like the ones used by covert marijuana growers. This will allow the mushrooms to breathe while helping to retain humidity inside the bucket. Depending on temperatures, spawn rate, and species, your bucket should be fully colonized in 10-21 days, or about 2 weeks.
Feel free to check in on your bucket to ensure it is colonizing well. Note the heat that the buckets should be putting off, as colonizing buckets are often warm to the touch. If multiple buckets are stacked too close together, the heat can actually cook and kill off the growing mycelium so proper spacing during colonization should be considered. Oyster mushroom mycelium has a sweet smell that's reminiscent of anise, so an incubation chamber with that scent is a good sign.
You may notice fungus gnats, which look like fruit flies, buzzing around your buckets. They won't kill your mushrooms but can be a nuisance and can spread contamination so feel free to dispatch them as necessary. Micropore tape can be placed over the holes of your buckets if the gnat issue persists. Dig a little under the straw, looking for the classic white cobweb-like mycelium of the oyster mushroom making its way through. If no mycelium is found, or if the bucket itself smells funky, it could be that the bucket has become contaminated. This could be from contamination, improper moisture content of your substrate, or poor environmental conditions. If that is the case, not to worry, you can always try again! That said, container growing is a very forgiving cultivation method!
If the colonization process is successful, you should see pins, or small clusters of mushroom-shaped structures poking through some of the holes in the bucket. Fruiting has begun!
Mushroom mycelium colonizing hydrated straw in a plastic bin
Step 6: Mushroom Fruiting
Golden oysters fruiting in straw by @mynexthobby
Now that fruiting has begun, it’s time to decide where to place your bucket for this important step. For outdoor fruiting, place your bucket outside in a well shaded area that does not receive much wind, such as a shady corner of your deck or inside a shed or garage. During this step it is important to make sure the mushroom pins do not dry out. If they get too dry, they will “abort” and fail to grow into full sized mushrooms. If the location you chose is too windy, you can drape a plastic bag loosely over the bucket. It could help to have a spray bottle during this step so that you can spray the mushrooms a few times daily to maintain humidity. Once pinning begins, you can expect to see full sized mushrooms in less than ten days. For best results place your buckets or containers in an area with naturally high humidity and plenty of shade.
For year-round fruiting, North Spore’s own BoomRoom Complete Kit is a great solution with a self-contained, fully automated mushroom fruiting and incubation chamber controlling humidity, CO2 levels, fresh air exchange, and spore filtration. Alternatively, you can fruit your mushrooms outside depending on the time of year and the specific mushroom you are working with, or in a homemade fruiting room with humidity control. For most oysters, optimum fruiting occurs when ambient temperatures are between 50 – 80 degrees F.
Step 7: Harvesting Your Mushrooms
Your bucket has pinned and the mushrooms have expanded to the point where it looks like the edge of their caps are beginning to curl upwards. This is when the mushrooms are about to release their spores, and is the best time to harvest them if not just before this point. If fruiting them outside, harvesting them early reduces the chance of bugs getting into them. Harvest the oysters in whole clusters by slicing them off at the back, against the bucket, with a sharp knife. Once harvest is complete you should cook them right away or store them in the fridge for 5 to 7 days in a paper bag. The earlier you use them the better!
Following harvest, you may get a second or even third flush of mushrooms through the summer and fall if you leave your bucket in a suitable (shady, humid) location or bury the entire block of straw in a vegetable garden or shady part of your yard.
Blue oysters fruiting at North Spore in 2015
Alternative Bucket Method:
Using Hardwood Pellets Instead of Straw
For species other than oyster mushrooms, North Spore developed a similar process to the one listed out above, but using hardwood pellets instead of chopped straw. In a large mixing tub, like the ones used to mix concrete that are widely available at hardware stores, pour 1 bag of 100% hardwood pellets and slowly add lime water with a pH of 12.5 to the pellets.
The pellets will start to fall apart and become a loose and moist sawdust mixture. Wear gloves and mix by hand and continue to add the lime water until all the pellets have broken down and the sawdust contains just enough water that by taking a handful of it in your hands you can just barely squeeze out a drop or two of water. This is called reaching the ‘field capacity’ of your substrate.
Mix sawdust or grain spawn into the bin with the hydrated pellets, and pack into sanitized buckets.
Follow the same incubation/fruiting instructions as above.
Growing in Containers Using Hardwood Chips
You can adapt the process above and choose to use hardwood chips and a hot water pasteurization instead of straw and a high pH bath. This will allow you to grow a wider variety of mushroom species, but will present different challenges. First, make sure the wood chips you source are not treated with any chemicals or antifungal agents. Tree services that routinely chip felled trees can be a good resource in areas with an abundance of hardwood tree species. Chips may also be sourced from pet stores or online retailers. Prefer a ready-made option? Our WoodLovr bags are a pre-sterilized and hydrated hardwood chip substrate if you want to skip the hard work and jump right to inoculation!
For this method you can use any type of growing container including but not limited to buckets, plastic tupperware bins, or monotubs. You can either create holes in the sides of your container from which mushrooms will grow, or remove the lid of your container to have mushrooms sprout from the top.
Nameko fruiting in a bucket with wood chips
Step 1: Heat Treat and Hydrate Your Chips
Place the hardwood chips in a large bin or tote, and fill with hot water. Your chips will float, so you might need to place something heavy on top to keep them submerged. You’ll want to bring the water temperature to between 65-85 deg C (149F- 185F). If you can’t achieve that with tap water, add boiling water to bring the temperature up. Let your chips sit in the hot water for 8+ hours, or until they have completely cooled off. The hot water partially pasteurizes the wood chips, killing some of the rival molds and bacteria, and hydrates and softens the chips making them more easily colonized by the mushroom mycelium.
Step 2: Cool and Drain Substrate
Once your chips have soaked and are sufficiently softened, pasteurized, and have had a chance to completely cool off you may drain off the water and inoculate them with your preferred mushroom spawn. We recommend using sawdust spawn for this method. Adding your mushroom spawn to piping-hot chips will likely kill off the mycelium, so ensure it is cool to the touch before inoculation. Chips should be fully hydrated, but not dripping wet. You can also drain the chips by just squeezing them out as you add handfuls to your container.
Inoculating your container involves simply building up alternating layers of wood chips and spawn until the container is full. Each layer of wood chips should be around 1.5” thick, topped off with a thin layer of spawn. You can wear sterile gloves if you are handling the spawn directly, but it is not necessary if you wash your hands prior to inoculating. The amount of grain spawn you should add to your substrate to maximize yield is known as the Spawn Rate, and a single, 5.5 pound bag of sawdust spawn can inoculate the equivalent of two 5-gallon buckets worth of substrate.
Step 3: Fruiting and Harvesting
Follow steps 6 and 7 from the Bucket Cultivation technique above for ideal fruiting location and harvest tips!