Before you start amending your garden, it’s good to know the plants that don’t like mushroom compost. Because while mushroom compost can provide your plants with necessary nutrients and improve soil structure, it can also cause harm.
What is Mushroom Compost?
Let’s start by reviewing what exactly mushroom compost is.
Mushroom compost isn’t made from decomposed mushrooms. Rather, it’s made from the substrate that mushrooms grow on.
This substrate is made from materials such as straw, corn cobs, spent brewers grain, and other organic materials. Mushroom growers also apply a “casing” made from limestone and peat moss.
Once workers harvest the mushrooms, farmers remove the used substrate and replace it. However, before the farmers remove the substrate from the growing house, they pasteurize it to kill pathogens and weed seeds.
From here, the spent substrate may be composted further.
Factors to Consider When Using Mushroom Compost
Before you start adding mushroom compost to your garden, remember that not all mushroom compost is created equal. Different companies produce mushroom composts with different properties. And different batches made by the same company can vary as well.
So before you start applying mushroom compost to your garden, consider the following.
Is the compost fresh or aged?
Fresh mushroom compost is made up of spent substrate from the mushroom growing area. Since it doesn’t go through a secondary decomposition process, it is a little chunkier than aged compost.
While some people say this fresh mushroom compost is too “hot” to apply to your plants, the folks at the Pennsylvania Association of Sustainable Agriculture say that it’s okay to apply to the soil and immediately plant.
However, it’s always a good idea to test the compost to check for dangerously high levels of soluble salts.
Aged mushroom compost is just fresh mushroom compost that has undergone further decomposition. The spent substrate is treated just like any compost pile, and therefore the materials break down even further. The end result is a compost that is finer than the fresh stuff.
What’s the pH and nutrient composition?
While two different mushroom composts may have differences in their pH and nutrient compositions, you can make some generalizations.
Researchers analyzed mushroom compost from 30 different mushroom farms in Southeastern Pennsylvania, the largest mushroom farming region in the US. They found these samples had an average pH of 6.6, which is a good pH for most plants. At this pH, most nutrients are available to plants.
The samples also had an average C:N ratio of 12.8:1 and acceptable levels of soluble salts.
Was the compost recently sterilized?
Some companies re-sterilize mushroom compost before bagging, so be aware that the compost may be devoid of microorganisms. Sterilized compost will still provide your plants with organic matter and nutrients, but it won’t provide a dose of beneficial microbes.
Plants that Don’t Like Mushroom Compost
While some people claim that some plants hate mushroom compost, they aren’t telling the whole story. It’s not that some plants don’t benefit from mushroom compost. Rather, it’s that the compost was improperly applied.
Mushroom compost, like all compost, should be treated as a soil amendment and not soil itself. What does this mean? You shouldn’t plant seeds or transplants directly into mushroom compost.
Rather, you should mix the compost in with soil. This helps to give your soil a boost in nutrients and organic matter while not damaging plants with excessive nutrients and salts.
Something else to consider is that some types of mushroom compost dry out quickly. Therefore, seeds planted in mushroom compost might not germinate due to a lack of moisture.
Be Aware of pH and Plant Needs
While most mushroom compost has a pH in the range of 6.0-7.0, some composts have a higher pH. If you find a mushroom compost with a pH above 7.0, you should not add it to acid-loving plants.
Some plants that like acidic soils include those in the Ericaceae family. These include blueberries, cranberries, and azaleas.
However, if you test your compost and find it has an acceptable pH, it’s fine to apply to these plants.
Best Practices for Adding Mushroom Compost to Plants
Despite what people say, most plants benefit from additions of mushroom compost. However, you have to incorporate this compost in the right way! If you just throw it on top of your plants, you’ll likely see some damage.
First off, don’t plant directly into mushroom compost. This rule applies to both seeds and transplants.
Due to the soluble salt concentration, seeds have a difficult time germinating in the compost. The salt concentration can also damage both seedlings and larger plants.
When you’re adding mushroom compost to your garden, mix it in with the existing soil.
Another tip is to get your compost tested!
If you’ll be using the same compost consistently, or adding the compost to a large area, it’s worth the money to pay for professionals to test your compost. Most extension universities offer compost testing services.
Add Some Mushroom Compost…Just Be Careful!
No matter what you hear, most plants can benefit from additions of quality mushroom compost. However, almost all plants don’t like mushroom compost that’s improperly applied or too high in soluble salts.
If you apply your compost following best practices, you’ll boost your plants with a source of nutrients and improve your soils. Don’t be afraid…be educated!