Cannabis growers have been working with organic nutrients and soil amendments for decades while dialing in their growth. There are hundreds of recipes for working with certain composts as a top dressing for beneficial bacteria and some avid growers have been experimenting with using these as substrates for growing.

Mushroom compost is often used as a soil amendment to provide organic matter for the microbes to break down to make into bioavailable nutrients for your plant. However, would it be beneficial to use it as a growing medium in itself? Would growing cannabis in mushroom compost be a good or bad thing?

You can use mushroom compost to grow cannabis plants but you’ll want to mix it with something else as it can be high in salts and other compounds depending on how it was made and mixed.

Mushroom compost generally works better as a soil rejuvenator rather than a substrate.

Do your due diligence and research the mushroom compost you are using to be sure that your plant is getting the right nutrients and that everything is balanced. The best way to accomplish this is to make your own mushroom compost.

What Is Mushroom Compost?

The interesting thing is that mushroom compost is actually more than one product. Some mushroom compost is the result of decomposing mushrooms while another is the compost that is actually used to grow mushrooms and then reused as compost for other plants.

Knowing the different types of mushroom compost will help you learn which type to choose for cannabis.

Mushroom Substrate

This type of mushroom compost is the substrate that commercial farmers grow mushrooms in. Mushroom compost is exceptionally good at, well, growing mushrooms and is used extensively in the farming process.

It is often mixed with materials like gypsum, straw, and various animal manures. This substrate is then pasteurized for sterilization to kill off bad bacteria and create a perfectly clean material.

Used Mushroom Compost

Alternatively, this is also a type of mushroom compost that you can buy on the market. Once farmers have used the mushroom substrate for a few crops it will be too low in nutritional value to grow more mushrooms so it is then recycled and resold as compost for other plants.

Using this as a soil amendment for denser soils is great as it’ll break it down over time. It is used extensively in organic cannabis grows to increase growth and resilience. It is also a slow releaser of nutrients so that your plants are fed over a longer period.

When you purchase it in the store it will be re-pasteurized again to make it inert; although some companies don’t. You can easily tell if it wasn’t sterilized if mushrooms start growing in your soil, which is never a bad thing.

Sterilization is done by injecting hot steam into the compost mass, successfully killing any errant seeds from weeds and unwanted plants. This process also eliminates all bad bacteria ensuring that no pathogens are lying in wait to attack your cannabis.

Is Mushroom Compost Good For Cannabis?

Mushroom compost is very balanced in terms of your NPK (Nitrogen, potassium, phosphorus) and with the addition of the organic matter for your microbes to break down, makes for a very good sustainable fertilizer.

It can be quite dense itself so if you were to use it as soil for your plants it’ll have poor drainage which could suffocate your roots. This is why it’s generally used to mix with another type of medium like coco or soil.

Can Mushroom Compost Burn Plants?

You generally won’t get a nutrient burn from using mushroom compost as for the most part a lot of the nutrients have already been used by the mushrooms they were grown in. However, due to the slow release characteristics of the compost itself, the plant will only get what it needs for nutrients.

There is always a chance of your cannabis getting burned as mushroom compost can burn sensitive plants. As long as you mix it with another grow medium you shouldn’t have any issues. Cannabis seems to handle mushroom compost just fine but a lot of other plants have a sensitivity to it that could potentially ruin the crop.

Pros And Cons Of Using Mushroom Compost

Pros

• It is one of the least expensive fertilizers to create and enriches grow mediums by providing essential nutrients.
• Since mushroom compost likes to hold onto water it increases the water retention of most soils it is added to.
• Starting the compost before winter and letting it mingle for an entire season will give it a quick boost when springtime comes.
• Many garden plants, including cannabis, benefit from the slow-release nutrient quality that feeds your plants for longer
• Mushroom compost is sustainable because it is just the used substrates from growing actual mushrooms. Less water is used as the compost is moist and fossil fuel consumption is lower as there is not as much processing needed

Cons

• Not all mushroom compost is equal. This means that sometimes you don’t really know what you’re getting, especially if buying in bulk. Some farmers use pesticides when growing their mushrooms and that can make its way down into the substrate.
• The quality of the substrate matters when it comes to mushroom compost. Pathogens and bad bacteria can be transferred to the cannabis plant and cause disease.
• Mushroom compost can become a problem if too much is added because it loves to hold onto water. The issue with this is that roots need oxygen to survive and if they are waterlogged by too much compost, will end up rotting.

Final Thoughts

Mushroom compost is an excellent addition to any grow medium and cannabis garden. The slow-releasing nutrients combined with varied nutrition will keep your soil healthy and productive.

Much like an animal and homemade compost, mushroom compost will provide as long as you use it in the proper setting. Ensure that your plants can handle mushroom compost before adding it to your plants.

Find out more about what is the best soil for growing cannabis, what is the living soil, and much more on our website!