Preparing Mushroom Grain Spawn: A Comprehensive Guide

Hydrated Whole Oat Mushroom Spawn

Grain spawn is an essential ingredient in mushroom cultivation, as it provides the fungi with necessary nutrients and moisture to flourish. The type of grain used and the preparation process are vital aspects to ensure successful mushroom growth. This article aims to detail the process of preparing mushroom grain spawn with a particular focus on whole oats, which has been found to be quite successful and relatively easy to use.

1. Selection of Grain

The first step in preparing your mushroom grain spawn is to choose the type of grain you want to use. There are numerous options available, but for this guide, we will focus on using whole oats, due to their availability and cost-effectiveness. Whole oats have been found to be highly successful for cultivating various types of mushrooms, making them a preferred choice for many cultivators.

types of grain

  1. Whole Oats: Easy to use and widely available, whole oats are a popular choice for mushroom growers. They have a great capacity to retain water and are quite cost-effective.
  2. Millet: This small-sized grain provides a large surface area for mycelium to colonize. Despite being slightly more expensive, it's a favorite among many cultivators for its efficiency.
  3. Rye Grains: They are one of the most commonly used grains due to their nutrient content, water-holding capacity, and the ease with which mycelium colonizes them. Rye grains are especially popular in cultivating species like Psilocybe cubensis.
  4. Wheat Grains: Wheat is a fantastic medium for mycelium growth due to its nutrient-rich nature. It’s particularly popular for growing gourmet mushrooms.
  5. Barley: Barley is often chosen for its high nutrient content and its ability to retain water well.
  6. Corn (Maize): Corn is used due to its availability and affordability, though it may not have as many nutrients as some of the other grains.
  7. Sorghum: Also known as Milo, this grain is often used in birdseed mixes and is similarly viable for mushroom cultivation.
  8. Wild Bird Seed (WBS): A blend of different grains (usually millet, sunflower seeds, and other small grains), WBS is a cost-effective option that provides a diverse nutrient base for mushrooms.
  9. Brown Rice: Often ground into flour and used in the PF Tek (a popular method of mushroom cultivation), brown rice is another good option due to its nutrient content.

Each grain type has its own pros and cons, so it's beneficial to experiment and find out which works best for your specific needs.

2. Soaking the Grains

After selecting your grains, the next step is to soak them. This process helps in hydrating the grains, a crucial element for mushroom growth. Depending on the climate in your area, the soaking time may vary between 12 to 36 hours.

In cooler climates, soaking the grains for a longer period is advisable, while in warmer climates, a shorter soaking time would suffice. There's no need to fret too much over the exact duration, but it's crucial to ensure the grains are adequately hydrated before moving on to the next step.

Approximately 600g of dry grain is required to yield 1 kg of wet grain after soaking.

3. Draining the Grains

Once the grains have been soaked for the required amount of time, they must be drained. A colander is a common tool used for this purpose, but other tools, such as a mesh drawer, can be perfectly suitable as well. The key is to allow all excess water to drain off. If you prefer, you can even make a DIY straining tool that suits your needs. 

Hydrated Whole Oat Mushroom Spawn

The mesh drawer in this picture is from Bunnings.

4. Loading the Spawn

After your grains have been soaked and drained, the next step is to load your spawn into bags or jars. This is where the actual cultivation process begins. Be mindful to evenly distribute the grain spawn, ensuring that there's sufficient space for air and mycelial growth.

Mushroom spawn bag on scales

Our mushroom grow bags are designed to accommodate between 2.5 to 3 kilograms of spawn. However, we typically fill them only up to 2.2 kilograms. This practice ensures ample space within the bags for shaking the contents, which aids in evenly distributing the mycelium. 

5. Sterilization

The final step in the preparation of mushroom grain spawn is sterilization. Sterilizing your grain spawn is a critical process that eliminates any potential contaminants that could hinder the mushroom's growth. The sterilization process usually takes between 1.5 to 3 hours. The exact duration depends on the size of your bags or jars; larger containers will need a longer sterilization time.


While there is an array of techniques available for preparing grain spawn, each with varying degrees of complexity, I've found this method to be the most efficient and user-friendly. Based on my experience, this approach strikes a balance between simplicity and quality, demanding minimal time and energy without compromising the desired results. It's the optimal strategy for those seeking to prepare high-quality grain spawn in an accessible, straightforward manner.

Ofcourse, for those who might find the process of preparing grain spawn too complex or time-consuming, there's a convenient alternative. I offer high-quality, ready-to-use mushroom spawn for purchase. This allows you to focus more on the exciting part of mushroom cultivation and less on the prep work, making the journey smoother and more enjoyable.