Five mushroom substrates and why we chose hardwood pellets

Growing mushrooms indoors requires safety, efficiency, and quality. The ideal substrate – the mycelium's food source – should meet those criteria to better the chances of harvesting a large cluster of healthy gourmet mushrooms.

Mushroom cultivators have many types of substrate to choose from – some work best with specific types of mushrooms and all types have their fruits and fallbacks. Time to act like mycelium and branch out to look at five options: hardwood pellets, straw, logs, manure, and coffee grounds.

Bags of hardwood pellet substrate on a cart

Hardwood pellets

Ideal for: Oyster mushrooms, Lion’s Mane, Chestnut mushrooms, Pioppino mushrooms, Shiitake, Reishi, and other mushrooms found on hardwood trees in the wild.

We at JCB Gourmet Mushrooms chose hardwood pellets as our main substrate because they are clean and a natural fit for the fungi we grow. We want to replicate the growing process for our mushrooms as if they were out in the wild. These mushrooms are saprophytic mushrooms that feed on and decompose hardwood trees.

We purchase hardwood sawdust in pelletized form. The pellets are easy to store and handle compared to straw; more on that later. We can simply scoop or pour the hardwood in the bags, promoting efficiency in the bagging process. Pelletizing the sawdust sterilizes the hardwood as well, partially reducing the likelihood of contamination. Bad bacteria and contaminants will have a harder time penetrating the pellet.

It is also easier to mix other supplemental substrates with the hardwood, such as soybean hull pellets or wheat bran. Oyster mushrooms love the added protein from soybean hulls; they sometimes turn to eat nematodes in the wild for the same supplements because of how quickly they grow.

Since the hardwood pellets are dense and packed together in a growing bag, we must be careful with how tightly we compress the bag when sterilizing and adding spawn to it. If the mix is too tight, the steam in the sterilizer will not be able to reach all the parts of the substrate to kill any contaminants. Likewise, it will be more difficult for spawn and mushroom mycelium to feed on the nutrients.

Mushrooms growing out of a bag with straw substrate.

"Awaiting harvest" by Wendell Smith is licensed under CC BY 2.0

Straw

Ideal for: Oyster mushrooms

Co-owner John Bakker first tried using pasteurized straw as a substrate before turning to hardwood pellets. It is a cheap option to grow mushrooms quickly, making the speedy Oyster mushrooms a good fit. Straw is the most common substrate for Oyster mushroom cultivators, according to the North American Mycological Association.

Straw bags are essentially another way to simulate a log, where the Oyster mushroom mycelium scavenge for nutrients and grow fruitbodies. The Oyster mushrooms can break down the straw’s fibres despite not being native to it in the wild, according to mycologist Paul Stamets in his book, Mycelium Running.

However, straw is messy, more difficult to handle, and not as versatile to our variety of mushrooms as the hardwood pellets.

The straw must be chopped up to become easier to pasteurize. Even still, the straw can be tougher to clean than the pellets. It must also be hydrated so it contains enough moisture for fungi to survive. Sure, we also add water to our hardwood pellet mixes and sterilize them, so the battle for efficiency comes down to how easy it is to store and add to bags.

The light straw can catch drafts and blow away when trying to stick the substrate into bags. It is also less dense, and therefore more difficult to store as much in a small space.

That all being said, mushroom growers may find straw more ideal for growing in larger plastic bags and either sitting the bag upwards or hanging them. The oxygen will easily make its way through the straw and allow the mushrooms more space to grow.

Shiitake mushrooms grow on a log.

"Our Shiitake Mushroom Log" by FreeWine is licensed under CC BY 2.0

Logs

Ideal for: Any mushroom that you can find on a tree.

There is nothing like simulating growing mushrooms on dead trees than literally growing mushrooms on a dead tree log.

Growers drill holes into the logs and either hammer in plug spawn or fill them with sawdust spawn. The holes are then sealed with wax.

Just like in the wild and like other substrates, the spawn will release hyphae, which will branch together to form mycelium, which will eat food in the log and grow outwards.

Unlike the other substrates, this format takes much longer to grow before getting your first harvest. In hardwood pellets or straw substrates, oyster mushrooms can take two to four weeks to go from spawn to fruitbodies. With logs, they will take at least one year. Afterwards, you can harvest roughly the same amount of mushrooms from a log per year as you would from a mushroom bag using pellets or straw.

While the logs are good for quality and safety, they simply are not nearly as efficient as other substrates.

Composted Manure

Ideal for: Button mushrooms

JCB Gourmet Mushrooms is located inside a former elementary school. Each classroom hosts a business. While composted manure loses most of its smell, we don’t want to take any chances!

Nevertheless, composted manure is the best way to grow the common Button mushrooms found in grocery stores. It is rich in nitrogen and is sometimes mixed with 20 per cent wet straw as a supplement.

The button mushroom spawn is mixed into the substrate and left in a wooden box as a bed. It takes about one month before harvesting the first flush, but the bed will produce mushrooms for up to half a year afterwards.

It is not recommended to grow Oyster mushrooms in manure since they achieve larger and better-looking yields in hardwood pellets and straw.

Oyster mushrooms grow on coffee grounds.

"Tree Oyster Mushrooms" by siraf72 is licensed under CC BY 2.0

Coffee Grounds

Ideal for: Oyster mushrooms

Saving coffee grounds for a substrate is an effective way to reduce waste and grow healthy food at once. They are usually too acidic for most garden plants, so growing Oyster mushrooms can be a fun alternative.

The consensus in academic research is that coffee grounds have earned consideration as mushroom substrate. Researchers in Romania found the Oyster mushrooms achieved positive and efficient results on substrate containing only coffee grounds. Another study concluded the coffee grounds are better suited as a supplement to straw substrate – the lower proportion, the better.

Like the pellets and straw, the coffee grounds are prone to contamination and must be sterilized by autoclaving, a method using high-pressure steam.

While Oyster mushrooms tend to do fine on coffee ground substrate, there is not enough evidence saying our other mushroom varieties, including the Lion’s Mane, Pioppino and Chestnut mushrooms, would fare as well.

Our hardwood pellet mix does the trick for all our mushrooms. It is packed with nutrients to grow healthy and strong mushrooms under the ideal conditions.

See for yourself with our mushroom grow kits. It does not take too much space or time to care for your mushrooms, and you can have your first harvest ready to cook in just over a week!

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