Mushroom compost, also known as spent mushroom substrate, refers to the leftover growing medium after mushrooms have been harvested. This nutrient-rich material can be an excellent addition to garden soils. However, mushroom compost also has some drawbacks to consider. Below is an in-depth look at the pros and cons of using mushroom compost in your garden.
Advantages of Mushroom Compost
1. High in Organic Matter
The primary benefit of mushroom compost is its high organic matter content. Materials like hay straw manure, peat moss, and ground corncobs are used to produce the initial mushroom growing substrate. Although the mushrooms absorb some nutrients during growth, much organic matter remains after harvest.
Adding organic materials to garden soil promotes microbial activity and improves soil structure. It helps loosen heavy clay soils and increases the water retention of sandy soils.
2. Rich in Nutrients
Mushroom compost contains a variety of macro and micronutrients that plants need for healthy growth
- Macronutrients – nitrogen, phosphorus, potassium, calcium, magnesium, sulfur
- Micronutrients – iron, manganese, zinc, copper, boron
These nutrients are released slowly over time, providing a steady feeding for plants. Mushroom compost can be an alternative to chemical fertilizers.
3. Ideal pH for Most Plants
Mushroom compost usually has a pH between 6.5-7.5, making it suitable for most garden plants. Acid-loving plants like azaleas and blueberries may not thrive at this pH level. But for everything else, the neutral to slightly alkaline pH is ideal.
4. Holds Moisture
The high organic matter content of mushroom compost enables it to hold onto moisture effectively. Adding mushroom compost to sandy soils can drastically improve their water-holding capacity. This helps reduce watering frequency in the garden.
5. Weed Suppression
Mushroom compost contains high levels of soluble salts. When used as a surface mulch, these salts inhibit weed seed germination and create a weed barrier. The fine particles also block light from reaching potential weed seedlings.
6. Available and Affordable
Mushroom compost is readily available in bulk at garden centers or direct from mushroom farms It is also very affordable compared to other soil amendments. Using local mushroom compost supports recycling of these organic materials
Disadvantages of Mushroom Compost
1. High Salt Content
The main concern with mushroom compost is its high soluble salt content. While the salt helps suppress weeds, it can also damage salt-sensitive plants. Seedlings and transplants are more susceptible than established plants.
Vegetables like beans, carrots, onions, and peppers can be harmed if planted directly into beds amended with mushroom compost. It is safest to use mushroom compost for ornamental plantings.
2. Unknown Origins
When obtaining mushroom compost from bulk sources, you don’t always know what went into the original mushroom substrate. There could be contaminants like residual pesticides or herbicides. This may not adhere to organic gardening practices.
3. Heavy and Dense
Mushroom compost is very dense and heavy, especially when wet. Adding too much bulk mushroom compost to garden beds can damage soil structure. It’s best to blend mushroom compost with other composts and fertilizers.
4. May Contain Pathogens
If mushroom compost is not fully composted, it could contain plant or human pathogens. Proper heating of the mushroom substrate during production should eliminate pathogens. But there is a slight risk if the compost is incompletely aged.
5. May Attract Mushrooms
Bits of mushroom mycelium may remain viable in spent mushroom compost. This can lead to mushroom growth in your garden beds. While mushrooms won’t harm plants, some gardeners view them as a nuisance.
Best Practices for Using Mushroom Compost
- Test soil and compost before application to determine proper rates
- Screen out large debris which may take longer to break down
- Blend mushroom compost with equal volumes of organic matter like leaves or straw
- Till mushroom compost into soil beds several weeks before planting
- Limit to 2-3 inches of mushroom compost tilled into beds
- Avoid direct contact between seeds/seedlings and mushroom compost
- Refresh beds amended with mushroom compost every 2-3 years
- Use as mulch for ornamentals, trees, shrubs, and fruit plants
- Monitor soil pH and salts after application
When used appropriately, mushroom compost can certainly boost soil health and provide nutrients. But potential drawbacks like high salts and unknown origins deserve consideration. With proper blending and application techniques, mushroom compost can be a cost-effective soil amendment for gardeners.
Why use mushroom compost?
Can mean either garden compost made at home or seed/potting compost: • Garden compost is a soil improver made from plant waste that has broken down, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used to grow seedlings or plants in pots. You can buy a variety of peat-free composts that are made from a mix of different materials, like loam, composted bark, coir, and sand, or you can make your own.
It is sometimes cheap and easy to get in large amounts from mushroom farms, soil and manure suppliers, and even some garden centers.
Traditionally made with well-rotted stable manure, mushroom compost is now generally made using composted straw.
Mushroom compost often contains chalk and is alkaline in nature. When using mushroom compost, make sure there aren’t any big pieces of chalk that can be seen, and only use it in small amounts. Instead, use well-rotted manure or garden compost, which react in a way that is neutral or slightly alkaline. This avoids excessive build up of chalk in the soil. A lot of the time, mushroom compost is sold without having been used to grow mushrooms first. Since it doesn’t contain chalk, it’s a great manure.
Note: there is no connection between spent (used) mushroom compost and the disease honey fungus.
Is Mushroom Compost Good For A Garden Or Should You Avoid It?
FAQ
When should you not use mushroom compost?
What plants do not like mushroom compost?
Can you put too much mushroom compost in the garden?
Which is better, mushroom compost or manure?
What are the benefits of mushroom compost?
Instead, using mushroom compost has benefits to disadvantages. Mushroom compost provides macronutrients like nitrogen, phosphorous, and potassium as soil amendments. Furthermore, it also supplies micronutrients like iron, calcium, and magnesium to soil health. It can improve the structure of compacted or clay-like soils to improve drainage.
Are mushrooms good for health?
Mushrooms are an excellent source of selenium and vitamin D. They are low in calories, fat free, cholesterol free, gluten free and very low in sodium. It is also rich in B2, B3, B5, ergothioneine, copper, potassium and beta glucans. B vitamins help in carbohydrate, protein and fat metabolism and nervous system. Mushrooms have beneficial effects in improving the immunity, could suppress the growth of breast and prostate cancer and weight management.
Does mushroom compost make a good soil?
Most mushroom compost has a good balance of organic compounds, making your soil fertile. Plus, it has a good mix of macro and micronutrients for overall plant growth. The relatively neutral pH makes most nutrients available to plants. Mushroom compost also improves the quality of sandy and clay-like soil.
Is mushroom compost eco-friendly?
This makes the compost an eco-friendly choice, as it is recycling and re-using a product that would otherwise serve no purpose. Mushroom compost that is used commercially usually has a straw base.
What is mushroom compost?
Mushroom compost can either be compost specifically made for mushrooms or mushroom compost which has already been used (called spent mushroom compost). Most gardeners purchase spent mushroom compost. The exact properties of each mushroom compost will vary, as there is no standard way to make it.
How does mushroom compost affect greenhouse plants?
Spent mushroom compost often contains chalk, and this has a liming effect. This can reduce the PH of acid soils and have a fertilizing effect. (This does not usually apply to unused mushroom compost.) Scientists Wang, Lohr and Coffey wanted to find out how mushroom compost would affect common greenhouse plants.