King Oyster Mushrooms on Sawdust

The Fruiting Block: Growing Gourmet Mushroom on Sawdust

Many types of mushrooms , specifically oysters, will do great and fruit heavily on straw logs as was explained in this post. However, most gourmet mushrooms will actually do way better if grown on hardwood sawdust supplemented with some sort of nitrogen rich supplement. Growing gourmet mushrooms on sawdust blocks will require a little bit more initial work than straw logs, and more equipment- mainly because sawdust blocks need to be pressure sterilized- unlike straw logs which need only to be pasteurized.

However, the process is quick, less mess, has lower chances of contamination, and provides a perfect medium for the mushrooms to grow large healthy fruits.

The basic recipe we use to grow all our gourmet mushrooms uses hardwood sawdust pellets, wheat bran, and water. Hardwood pellets are used because they are readily available at local retail stores or online, and store easily. Make sure to get hardwood pellets and not softwood pellets. Mushrooms do not grow well at all on softwood. The pellets are small and only expand when soaked in water. Wheat bran is used as the nitrogen rich supplement. It can be found in small quantities at your local grocer, but can be quite expensive.

A better option is to buy some from a feed or farm store. Oat bran can also be used, but we have found wheat bran to be the most effective. As for water, the trick is to add just the right amount to get a proper moisture content. You don’t want your block to be too wet or too dry. The following recipe works great for use, but you may have to adjust it slightly to suit the specific moisture content of you pellets.

FreshCap now sells grow bags for making supplemented sawdust friting blocks!

The Fruiting Block Recipe:

For every 5 lb fruiting block:
5 cups of hardwood pellets
1.4 liters water
1-1/4 cups wheat bran

How To Grow Mushrooms on Supplemented Sawdust Fruiting Blocks

Step 1: Measure out the components

The above recipe will make a block weighing approximately 4 lb 4 oz. Your final bock should end up weighing 5 lbs after you add 12 oz of grain spawn. Its best multiple blocks at a time, as many as can fit inside your pressure sterilizer. This presto pressure canner is relatively cheap and can hold 4 large blocks, made with 20 cups pellets, 22.5 cups water and 5 cups wheat bran

Hardwood pellets for mushrooms.
Step 2: Add Water to Sawdust Pellets

Place your hardwood sawdust pellets in a large tote or suitable container for mixing. Add the correct amount of water and mix until the pellets have broken up into a loose sawdust texture. Adding warm water makes the sawdust break up much quicker but is not necessary, as cold water works just fine. It may take a while to mix up all the pellets, but you want to be sure it has all broken down because the mushrooms will have a much harder time breaking down the hardened pellets.

Step 3: Add Wheat Bran

Once the sawdust is mixed up and all the pellets are broken down, add the correct amount of bran. You can increase the amount of bran to add more nutrition into the block, but more bran will increase the chance of contamination and adding more will eventually lead to diminishing returns. Make sure to mix the bran thoroughly and evenly throughout the sawdust.

Mushroom grow bag.
Step 4: Add Mixture to Grow Bags

Weigh out the proper amount of sawdust/bran mixture and add it to a grow bag. I add 4 lbs 4 oz to each grow bag, which makes a 5 lb block once the spawn is added. Try to not get the mixture on the sides of the bag above the block, as this can lead to contamination problems later on. The bags are specially made for growing mushrooms. They are made of poly propelyne which can withstand the sterilization process. The Filter patch allows the mushrooms to breath while they are colonizing the substrate.

Step 5: Fold the Bags Down

The tops of the grow bags are gusseted and should be folded down in a specific way, with a filter fitted in between the gussets. This prevents contamination during cooldown after sterilization. When the bags cool down, air will be drawn into the bags. If there is no filter between the gussets, dirty air can sneak through and ruin your project. By slipping a filter in between the gussets you can alleviate this problem. Once the filter is slipped in, fold the top of the bags over a couple times. For the filter, you can use a cut piece of tyvek or a square cut from a painters suit.

Step 6: Pressure Sterilize

Load your pressure sterilizer with the bags stacked on top of each other. Make sure to use jar lids or something that will keep your grow bags from making direct contact with the bottom of the sterilizer, as this could cause the bags to burn. Fill with the water to just below the top of the bottom bag. You will need more water than when making grain jars because you will be sterilizing for much longer. Also, be sure to add a plate or something heavy to the top of the bags. If you don’t do this crucial step, you run the risk of the bag clogging the weight and the pressure relief valve on the pressure cooker. This could cause pressure inside the cooker to reach dangerous levels. Pressure sterilize your bags for 2.5 hours. This seems like a long time, but it is necessary for the heat to fully penetrate the the inside of the block and fully kill all contamination.

Sterilized fruiting block

A fruiting block post-sterilization ready to be inoculated with grain spawn. Notice how the filter patch is slipped in between the gussets and the top is folded over twice.

Step 7: Cool Down and Inoculation

Allow your fruiting blocks to cool down for at least 8 hours. I like to pressure sterilize at night and allow the pressure cooker to fully cool down over night. Anything over 38 deg C can potentially kill your mycelium. Fruiting blocks are best inoculated in front of a laminar flow hood. You can do it in a glove box or similar, but you will increase your chances of contamination. Once you have added grain spawn to your sawdust block, tie off the top of the bag with a piece of wire or zip tie and set on a shelf. Shake the bag to evenly distribute the individual grains throughout the bag. This will speed colonization of the block.

Grow bags colonizing

Grow bags colonizing on a shelf.

sawdust grow blocks

Grow bags after inoculation. Note the mixing of the grain spawn.

Step 8: Allow to colonize

Depending on the amount of spawn and type of mushroom you are trying to grow, it might take anywhere from 10-21 days for the mycelium to take over the block. There is no benefit to shaking the bag during colonization, just allow the grain spawn to take over the block naturally. Periodically look over the bag to check for any signs of contamination. Usually, it is not worth opening contaminated bags in your grow room, so it is better to just throw them out if the bags look contaminated.

Step 9: Fruit!

Once the bags have fully colonized consolidated, they are ready to fruit. Different mushrooms have different requirements from this stage, but for most gourmet mushrooms, just cut off the top of the bag and place inside your growing environment. From here, the block should start to pin from the top of the block, and eventually form mushrooms. Closely monitor humidity and temperature to see what your block needs.

yellow oyster mushroom on sawdustPink Oyster Mushroom on sawdust
Step 10: Harvest

Once you are satisfied with the size of your fruits, they are ready to be harvested and enjoyed. The best strategy is to cut the mushrooms off at the stem trying not to damage the underlying block, since it can be used to get 3-4 flushes if properly taken care of. Once harvested, simply place your block back into a fruiting environment and wait for a subsequent flush. Watch closely for contamination as your blocks gets older. Often new mycelial growth will take over the harvested portions of the block before a second flush arrives.

Thanks for reading and good luck with your grows!

-spread the spores-

Want to grow mushrooms at home? Here are a few things you’ll need to be successful.


Comments 34

  1. Would a liquid inoculation be easier via hypodermic needle, rather than opening the bag up? Just like getting a shot at the doctors office. Clean the area with alcohol, flame needle, administer LI and then tape the tiny hole up. Then you could have successful grows without a flow hood, at least for a hobbyist.

    1. Post

      Absolutely, as long has you have a clean culture, this should work just fine. Let me know how it works for you! I know some people make “self healing injection ports for this very purpose. Use a high temp silicone sealant to make them on mason jar lids. It might also work just directly through the bag as you described, but I have never tried.

  2. How bad of an idea would it be to put the premixed sawdust, bran and water in a pressure cooker without bags? I’m actually going the bucket and mason jar route to cut down on plastic usage. The only thing I worry about is the sawdust keeps expanding in the pot and could possibly clog holes, creating a potential bomb in my kitchen. I was just wondering if you may of done this or know someone who has successfully. Thanks

    1. Post

      Hi John! I am not sure about this… it may sterilize the substrate just fine, but as soon as you open the pressure cooker it will again be contaminated. The bags provide a way for the substrate to remain sterile the whole way through. The reason we can pasteurize straw and then inoculate it in the open air is because straw isn’t nearly as nutritious and won’t contaminate as fast.

    1. Post

      Hey Bryan!

      Pretty much any kind will work! I use a mix of all different types of hardwood, usually in pellet form. Straw works really well for oysters as well!

    2. If you wanna do some outdoor Oyster Totems , Cottonwood works great !
      You can seal the Cuts between the Rounds, and between the Cardboard and the first Round with wet Clay.
      Also the Top of the Top Round seal with Clay .I just built a few more since my first Totem was an amazing success.
      Very inspired Steve

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  3. Hi Tony,
    why must sawdust be pasteurized by pressure and not temperature?
    Also, what process would you recommend when pasteurizing coffe grounds?

    1. ∗Edit…
      the coffee grounds have not been pasteurized in a coffee machine,
      but rather have been used to make cold brew,

      1. Post

        Hi Jack! It is actually the higher temperature that is required to sterilize, but the pressure is what is needed to get steam to that temperature. At 15 PSI, the steam temperature inside the cooker is 121 deg C, enough to kill off all contaminates. If you tried to do it at atmospheric pressure, the temperature would not be able to rise above 100 deg C. For coffee grounds, I would suggest full sterilization in a pressure cooker, but many people have had luck with just pasteurizing in a hot water bath for 90 minutes (65-82 Deg C). Hope that helps!

  4. I live very close to a wood shop, they have truck loads of hardwood sawdust, could I us it instead of the wood pellets?

    1. Post

      Absolutely, in fact it may be preferable! Just make sure that there is not a lot of glue or anything in the sawdust… if you can get pure hardwood sawdust (beech, elm, maple, oak ect.) then you have hit the jackpot! Hardwood Fuel Pellets work well for people who do not have easy access to pure sawdust.

  5. Hello

    I have two questions for you please:

    1. I have a small steam distillation plant for producing essential oils such as Cinnamon leaf oil. This is running at atmospheric pressure. I can direct and inject the steam deep into the middle of the saw dust bag using 2 mm bore copper tube … with a thermal lance arrangement. In addition I can expose the PP bags filled with saw dust to Ultra violet light too for sterilisation. Your comments would be highly appreciated on this sterilizer procedure.
    2. What sort of moisture level or wetness do we have to maintain in the saw dust media once the sterilizer procedure is over?

    Thank you

    1. Post

      Hey Mal!

      1. I have never tried this, but I don’t see why it couldn’t work, other than the fact that the temperature of the steam may be too low to kill all the contamination. It may be worth a try though. You may just have to steam them for a much longer time, which likely won’t be all that efficient.

      2. The sawdust substrate is contained in the bag, and the moisture level doesn’t change much.

      Hope that helps!


  6. Hi Tony,

    I’ve got a portobello liquid culture, can I use that to inoculate sawdust/rice bran/gypsum cake?
    Or I need a specific formula for portobellos spawn?

    English isn’t my first language,

    1. Post

      To be honest, I am not that well versed in growing Agaricus species (Portabello included) – but I would think they require some sort of composted substrate, such as manure in order to grow properly. Portabello is not a wood loving species like the other gourmet varieties.

  7. You mention in step 4 “Weigh out the proper amount of sawdust/bran mixture and add it to a grow bag. I add 4 lbs 4 oz to each grow bag, which makes a 5 lb block once the spawn is added.”
    But reading further you don’t mention when to add the grain spawn. Also in other recipes on your site the grain spawn is not mentioned. Is it necessary?
    I am trying to find an easy recipe to start my first batch in jars and inoculate via syringe.

    1. Post

      Hey Sorcha! Thanks for reaching out! The spawn is added to the block after the block is sterilized. Grain spawn is used as a way to “inoculate” the block with the mushroom culture. Once the spawn is added and mixed, it will start to grow through the block, eventually fully colonizing and fruiting. If you are inoculating from a syringe, you essentially have a “liquid culture” which can serve the same purpose as grain spawn. It can be added directly to the block, without the need for grain spawn, although the results might not be that great. A better option is to inoculate sterilized grain and make your own grain spawn, which can be added to the block as described above. Hope that makes sense!

  8. Hi Tony, Love your site, Could you suggest more information on how to fold the bags in step 5. I think everything else was expertly explained.

    1. Post

      Sure thing! Basically, the idea is to fold the top of the bags over twice with the filter slipped in between the gussets. BUT- I have also been experimenting with simply folding the top of the bag over once, without the filter- and so far it has been working just fine. As long as you use the bag relatively quickly after cool down, you should be OK with a simple fold over. Hope that helps!

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  9. Hi Tony,

    Thanks for the wonderful information. I am trying to start a mushroom farm in central himalayas in 2018, so am lapping up what all you put down on your site.
    Is there any alternative to disposable plastic bags? They have already created a lot of pollution in India and I want to avoid them if possible. For oysters, I did read around a lot and think that reusable plastic buckets with holes punched in them is a good idea. I will be trying some sample runs next week. However, is there any way for growing shiitakes on any reusable containers?

    1. Post

      Hi Prashant, thanks for reaching out! I haven’t tried to grow Shiitake’s in anything but plastic grow bags, but I don’t see why you couldn’t. Try experimenting with buckets and see what you can come up with! The nice thing about grow bags is that they are autoclavable, meaning that you can sterilize the bags and the substrate at the same time, ensuring a sterile grow. All the best!

  10. Hey Tony,

    I’ve heard of some folks hydrating their Hardwood Fuel Pellets, and then inoculating them without sterilizing them before inoculation. Also, I’ve heard of other people pasteurizing the Hardwood Fuel Pellets, and then inoculating them. However, in your instructions you sterilized before inoculating.

    How did you go about deciding sterilizing your pellets before inoculation was the best move? Can you achieve similar results by either pasteurizing, or by skipping the sterilization/pasteurization process all together?

    1. Post

      Hey Ben,

      Thanks for reaching out! Yes, the reason I need to sterilize the blocks is because I add supplementation, namely oat bran or wheat bran. Without sterilizing, this would contaminate quickly. However, if you don’t use supplementation, you can likely get away with a simple pasteurization. I will do a post on this soon!

  11. Hello Tony,

    I plan to grow lion’s mane soon and wonder if I absolutely need to use grain spawn in the filter-patch bags of hardwood sawdust? May I instead use pieces of bought colonized sawdust block?

    I’ve never handled sawdust block before. I have though in the past (with other kinds of mushroom) started from spore prints and done the whole nine yards, from isolation etc. all the way through to grain spawn or lc and fruiting- this took quite some time but was always successful. This is for a parent who had a stroke, and time isn’t a luxury, also I want to grow a lot continually for a while. Cost why I’m considering this method.
    Second question that just occurred to me: In general, is bought sawdust spawn typically sterile?
    Thanks and sorry for the long questions.

    1. Post

      Hey David!

      Thanks for reaching out! Yes, sawdust blocks should typically be sterile. You should be good to go, sounds like you have the experience and passion to make it work!

  12. Hi Tony,
    I have a block of coffee grounds colonized with oyster mushrooms (from a grow kit). It is ready to fruit, but I was thinking I might use part of it to start some new sawdust blocks. Do you think it would be effective to add small pieces of the coffee ground block to the sterilized grow bag in place of grain spawn?
    Thank you for sharing your growing process. It’s really good information!

    1. Post

      Hey JR! Thanks for reaching out! Yes, I think this is a great idea, as long as you keep everything sterile. Is the fruiting block still in sterile condition or has it been opened up? I am thinking you should be OK, as this is a great way to get more out of your fruiting kit.

  13. Hi, Tony!

    In some of the pictures in the Growing on Sawdust section, casing soil has been added to the top of the bag. What are your recommendations on making and using casing soil? I am playing with winecaps right now and I hear that casing soil makes a big difference.

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