Mushroom Spawn & Grow Kits


Pearl oyster mushrooms fruiting indoors from a 5 lb. grow kit made with supplemented sawdust.

Now Accepting Mushroom Spawn &
Grow Kit Orders for Summer 2020

For a limited time, we are now accepting orders for both grain and sawdust spawn as well as supplemented grow kit bags and ‘fungi pails’ that will be made available for pick-up in July. Due to popular demand and the limitations of a small business, only a select number of spawn, grow kits and ‘fungi pails’ can be produced during a single production run.

If you are not able to have your order processed this time, please join our e-mail list (sign-up form on the home page) so that you can be notified at a moment’s notice the next time mushroom products are made available. Please use the order form found below the submit your order and you will receive an e-mail response as a confirmation. Thank you for your interest and support of grass roots mycology in Manitoba!


1 lb. jars of grain spawn incubating. Tyvek filter discs are used to keep the contents inside the jars sterile.

Ready to start growing your own mushrooms? We’ve got you covered. Fresh mushroom spawn, in addition to a properly amended nutritious substrate material, is all you need to start growing beautiful and delicious mushrooms right at home. If you are unsure where to begin or how to use and care for your mushroom spawn, please consult the articles below to learn more or Contact us if you have any specific questions.

Spawn from River City Mushrooms is available in 1 pound quart size mason jars ($10) or 5 pound sealed polypropylene mushroom bags ($30, or 4 for $100). Each of these sizes is available as grain or sawdust based spawn. Grain spawn is produced using certified organic Manitoba grown rye grain and sawdust spawn is produced in part using locally sourced hardwood sawdust.

Grain spawn is best used when growing mushrooms indoors on plain sawdust, supplemented sawdust mediums or pasteurised chopped straw both indoors or outdoors. Sawdust spawn works best for inoculating hardwood logs (in addition to plug spawn) which will be incubated and allowed to fruit outdoors over the course of several years or inoculating outdoor wood chip beds which will also be perennial.

‘Ready to fruit’ grow kits are also available in limited quantities. These 5 – 6 lb. blocks are prepared using a special recipe of supplemented hardwood sawdust and unlike spawn do not need to be mixed with any additional materials. Each order will come with an electronic copy of a document containing detailed instructions that will inform you on how to care for and harvest your fresh crop of home grown mushrooms.

All orders of spawn and grow kits will be made available soon after they are inoculated with the mushroom culture of your choice. As such, an incubation period of roughly 1-3 weeks (up to 2-3 months for some species) is required after the inoculation date for the mycelium to colonise the substrate within before the spawn or grow kit can be opened up and used.


Species & Strains


  • Pearl Oyster (Pleurotus ostreatus)
  • Pathfinder Oyster (Pleurotus ostreatus)
  • Elm Oyster (Pleurotus ostreatus)
  • King Blue Oyster (Pleurotus spp.)
  • Black Pearl King Oyster (Pleurotus ostreatus x eryngii)
  • Pink Oyster (Pleurotus djamore)
  • Yellow Oyster (Pleurotus citrinopileatus)
  • Lion’s Mane (Hericium erinaceus) * heat tolerant strain
  • Almond Agaricus (Agaricus subrufescens)

Beautiful, healthy white mycelium colonizing sterilized rye berries to create grain spawn.

What is Mushroom Spawn?


Mushroom spawn is the mycelium of a fungus that has been inoculated into grains or into hardwood sawdust under sterile conditions. Cleanliness is important so as to prevent the growth of bacteria, yeast, or other fungi that may act as competitors to your desired mushroom species. Spawn is your best choice for inoculating large volumes of a suitable substrate material quickly and efficiently to yield bountiful crops of mushrooms.

Mycelium is the body of a fungus and is comprised of a vast, interconnected network of filaments that make up the structure of the fungal organism. Mycelium can be easily recognized as a fine, usually white, thread-like material growing throughout decomposing logs, branches, rotting leaves, within the soil or virtually any other dark, moist and sheltered environment.

The material that the mycelium of a fungus lives within is known as substrate. Substrates are nutritious, organic materials such as wood, soil, manure or compost which the fungus breaks down by releasing digestive enzymes. Substrate materials can vary greatly depending on the individual requirements of the species or strain being cultivated.

Mushroom spawn, when mixed or ‘planted’ into a nutritious medium such as wheat straw or sawdust, produces new threads of mycelium and begins to break down and digest this material. Only when the mycelium has completely encased or colonized the substrate will the fungus begin to shift from vegetative growth to reproduction and can then be encouraged to produce mushrooms, which are the reproductive structures of the fungus.

When certain environmental conditions are present (usually elevated oxygen levels, high humidity and a change in temperature), this stimulates the mycelium to ‘fruit’ and produce mushrooms which can then be harvested and enjoyed fresh or preserved for later use. Fungi are fundamentally different from both plants and animals, yet there are parallels that can be drawn between gardening with both plants and fungi.

A thorough understanding of the environmental requirements necessary for proper mushroom development such as light levels, fresh air exchange and humidity in addition to learning to formulate, prepare and handle substrate materials properly is necessary in order to successfully grow mushrooms using spawn.

Please be sure that you have educated yourself before choosing to work with mushroom spawn. We cannot be held responsible for failure if the mushroom spawn was not stored properly, handled incorrectly or grown under detrimental conditions. Just like vegetable gardening, mushrooms require certain environments if they are to flourish and reward you with a harvest for you diligence and patience.

If you would like to learn more, attending a public program or interactive workshop specifically discussing mushroom cultivation is the best way to gain first hand knowledge from a skilled cultivator and have your concerns addressed in person. Websites, online forums, field guides, instructional videos and cultivation manuals are all excellent sources of detailed instructions, varied perspectives and useful techniques to help guide you to make the decisions that are right for you.

You can find a detailed list of reputable literature websites and more on the Resources page. This section of the website is being constantly updated in order to provide you with the most relevant and up to date information possible. As always, please reach out and Contact Us if you have any specific or urgent questions or concerns that you are having trouble finding answers to elsewhere.


How do I Store Mushroom Spawn?


Do not open the jar or bag
until you are ready to use it

It is generally accepted that mushroom spawn is best opened up and mixed with a suitable, nutritious substrate material immediately after the contents have been completely colonized by the mycelium within. This allows the cultivator to take advantage of the continuous, vigorous growth of the mycelium and helps to ensure rapid, thorough growth once introduced to your chosen substrate medium.

However, mushroom spawn is a fairly stable product that can be safely stored for several months if it is not possible to use immediately. If the spawn has not yet been fully encased in healthy white mycelium, then more time most be provided for full colonization to occur so as to limit the chance that mold, bacteria or other microorganisms could compete with your desired mushroom species or strain and potentially contaminate and ruin your project.

If this is the case, then mushroom spawn can be placed in a spot in your home that has decent ventilation, is away from cold drafts and direct sunlight, and ideally off of the floor to finish growing. Room temperature is often ideal for more species and strains of edible and medicinal fungi, although slightly cooler temperatures (~ 5 – 15°C) are much better than too warm (~ 25 – 35°C). Temperatures in excess of 30°C can be harmful, as can direct sunlight for any length of time.

Temperatures below 10°C can cause the mycelium to grow much slower and refrigerated temperatures (~ 1 – 4°C) often cause the mycelium to enter a state similar to hibernation and hardly grow at all or very slowly. Freezing temperatures are lethal to most species if stored as grain or sawdust based spawn, so never put spawn in your freezer or or store outdoors during the winter months.

Indirect light is beneficial to the growing mycelium as they grow and develop, so avoid storing them away in dark cupboards or pantries which also tend to have poor or virtually nonexistent airflow. Places in the home where ambient temperatures fluctuate wildly are not necessarily detrimental but will likely affect the rate at which the mycelium can acclimatize to the surrounding environment and should therefore be avoided in order to produce consistent growth.

On top of the fridge, on a shelf in the living room, on the counter in a kitchen or on a bedside table or desk are all good places to store your mushroom spawn, as long as direct light is avoided but indirect light is available and the room has good ventilation. Also avoid storing your spawn near sources of possible sources of mold or bacterial contamination such as compost buckets, trash cans, or in or near washrooms.

Under ideal conditions, mycelium should be visible growing within the spawn at around 1-2 weeks after the inoculation date found on the jar lid or bag label. If the spawn was inoculated recently and the grain or sawdust inside is around only 20-30% covered by mycelium, giving the jar or bag a vigorous shake or gentle massage, respectively, for around 20 seconds or so helps to break up the growing mycelium and redistribute hyphal fragments, helping the remaining substrate to colonize faster.

Once the mycelium has completely covered the grain or hardwood sawdust and has had a chance to briefly consolidate for a couple of days, it is ready to be used. If you are not yet ready to use your mature spawn, simply place the spawn in your fridge or a cold cellar between 1 – 4°C until you are ready to incorporate it into a prepared substrate mixture of your choice.

If the mushroom spawn is fully colonized and not chilled within a few days, the mycelium may enter a state of senescence or prolonged rest which may result in a noticeable decline in vigour once opened up and mixed with substrate material. Storing the recently colonized spawn under cooler temperatures prevents it from become over-mature and stalling once it is time to grow again. Spawn that has been chilled is best allowed to warm back up to room temperature for a day or so before being opened up and used.


How Do I Use My Spawn?


When the grain or sawdust medium within your jar or bag of mushroom spawn is completely covered in healthy, white mycelium and you have prepared (and sufficiently hydrated) your chosen substrate medium, it is time to bring the two together and begin the process of growing your own mushrooms. Before you open up your jar or bag of spawn, it is necessary to break up the individual particles of consolidated mycelium within.

Doing this allows for a more thoroughly mixed substrate preparation after the spawn has been introduced and allows the mycelium to begin growing within your substrate from many hundreds if not thousands of individual inoculation points. These isolated islands of hyphal growth will eventually merge and consolidate once again into a fully colonized substrate that then begin to support the growth and development of mushrooms.

In order to achieve this, jars of mushroom spawn can be opened up and a spoon or other small utensil can be used to break apart and loosen up the media within below applying it to your substrate. Bags of spawn, since they are pliable, can be gently massaged, rolled or smacked to break apart the individual grains or sawdust particles before being opened.

Mushroom spawn can be added to your substrate mixture of choice at a ratio of 1 part spawn to 3 or 4 parts substrate by volume. This will result in the spawn making up 25-33% of the total volume of your new fruiting material. We recommend using a 1:3 or 1:4 ratio of spawn to substrate for beginning and novice mushroom cultivators since this allows for a higher volume of spawn in the final fruiting material. This often results in faster colonization which will discourage contaminates from proliferating as well as potentially higher yields.

Commercial mushroom growers, working under mostly if not entirely sterile conditions, often inoculate at ratios of 1:5, 1:8 or even as low as 1:10 or even 1:20. When you are working in the open air and not under sterile conditions, working with higher amounts of spawn to substrate results in a greater chance of success while you are still developing your own techniques for handling and mixing spawn and substrate.

As you continue to work with mushrooms, diversify the species and varieties that you work with and refine your techniques, you can begin to work with smaller ratios of spawn to substrate and still experience adequate colonization and yields. Oyster mushrooms (Pleurotus spp.) and wine cap stropharia (Stropharia rugosoannulata), the first choices for many inexperienced and new mushroom growers, are particularly adaptable and aggressive enough to handle less than ideal conditions and still perform well.

For more information on the specific substrate formulations that different species and strains of mushrooms require in order to perform at their best, consult the Resources page for lists of recommended, books, websites, online forums and videos that will help you to make the most informed decision possible.

River City Mushrooms also offers interactive, hands on workshops and programs throughout the growing season illustrating how to successfully implement and design several different cultivation procedures suitable for the species and strains of mushroom spawn available through the website. To learn more, be sure to follow us on Facebook or Instagram and check back to the home page often for when upcoming programs and courses are advertised.

Thank you for your interest
in fungi & mushroom cultivation!
Happy Growing