Mushroom Compost: Making Process Explained

Mushroom compost is a by-product of mushroom farming. It is made from the substrate in which mushrooms are grown, which typically includes straw, hay, poultry or horse manure, and crop residues such as corn cobs and cocoa shells. The substrate is composted for about 30 days at 160 degrees Fahrenheit to kill weed seeds, pests, and disease pathogens. After the mushrooms are harvested, the substrate is removed and processed into a consistent, homogeneous by-product called mushroom compost. This compost can be sold as spent mushroom compost and used as a soil amendment for lawns, gardens, and container plants. It is a slow-release organic plant fertilizer that improves soil structure, increases water retention, and provides nutrients for healthy plant growth.

Mushroom compost ingredients

Mushroom compost is a by-product of mushroom farming. It is made from a mixture of agricultural materials, such as straw from horse stables, hay, poultry litter, ground corn cobs, cottonseed hulls, cocoa shells, peat moss, and other natural organic substances. These products are formed into a rich organic medium that serves as the nutrient source for mushrooms.

The exact composition of the growth substrate varies from grower to grower. However, one of the most popular commercial blends of mushroom substrates is a mix of wheat straw, gypsum, and chicken or horse manure. Other common ingredients include hay, straw, corn cobs and hulls, and poultry or horse manure.

Additional materials like gypsum, peat moss, lime, soybean meal, and various other organic items may also be added to the compost. The substrate is then composted for about 30 days at 160 degrees Fahrenheit to kill weed seeds, pests, or disease pathogens.

After the mushrooms have been harvested, the medium's ability to sustain mushroom growth is exhausted, and it is replaced with fresh mushroom soil for a new batch of mushrooms. The leftover compost is then disposed of and sold as fertiliser.

It is important to note that mushroom compost should be used with caution due to its high soluble salt levels and alkalinity. These salt levels can kill germinating seeds, harm young seedlings, and damage salt-sensitive plants. Therefore, it is recommended to temper the alkaline levels of mushroom compost with a product like aglime.

Pasteurisation

There are different methods for pasteurising mushroom compost, depending on its ingredients and intended use. One common method is steam pasteurisation, where steam is used to raise the temperature of the compost to approximately 160 degrees Fahrenheit for about 30 days. This temperature and duration are crucial for effectively killing weed seeds and any harmful organisms that may be present.

Another method for pasteurisation involves boiling water. In this technique, the compost materials, such as straw, manure, or coffee grounds, are placed in a mesh or cloth bag and submerged in a large pot of boiling water. The heat is then turned off, and the compost is allowed to steep for about an hour to an hour and a half. This method is simpler and more accessible for small-scale compost preparation.

For composts made from hardwood sawdust, a sterilisation process is recommended instead of pasteurisation. Sterilisation involves cooking the substrate in a pressure cooker at a higher temperature and pressure (over 250 degrees Fahrenheit at 15 PSI) for an extended period (approximately 2.5 hours). This more intense process ensures that any potential contaminants in the sawdust are eradicated.

It is important to note that the pasteurisation process may vary depending on the specific recipe and ingredients used in the mushroom compost. Additional materials, such as gypsum, peat moss, lime, soybean meal, and other organic items, can be added to the compost, and these may have specific temperature requirements during pasteurisation. Therefore, it is always advisable to follow specific instructions for pasteurisation provided by reliable sources or manufacturers.

Curing

Timing and Duration:

Purchase or prepare fresh mushroom compost in fall, winter, or early spring to allow for sufficient curing time. This timing ensures that the compost has ample opportunity to age and that any excess salts have been leached out before the planting season.

Leaching of Excess Salts:

Excessive amounts of soluble salts, such as calcium, magnesium, and potassium, can be harmful to certain plants. Curing helps to reduce these salt concentrations. Rain and snowfall naturally leach excess salts from the compost over time. Irrigation can also be used to achieve the same effect if natural precipitation is insufficient.

Pasteurization:

Before curing, it is essential to pasteurize the mushroom compost to eliminate any pests, pathogens, or weed seeds. This can be done by steam-treating the entire batch of compost or, for compost made from straw, manure, or coffee grounds, by submerging the material in a boiling water bath for 1-1.5 hours.

Sterilization:

If sterilization is required, a more complex process is involved. One effective method is to use a pressure cooker and cook the substrate at 15 PSI, above 250 degrees Fahrenheit, for 2.5 hours. This ensures that any harmful organisms are eradicated, making the compost safe for use.

Monitoring and Testing:

During the curing process, it is important to monitor the compost and ensure it maintains adequate temperatures. Additionally, you can request a detailed laboratory analysis from your supplier to guarantee the quality and reliability of the mushroom compost. This analysis can provide information about nutrient availability, salt concentrations, and the presence of any contaminants.

Uses

Mushroom compost is a useful addition to your garden. It is a recycled compost that has already been used in the mushroom-growing industry. It is a byproduct of the edible mushroom industry, repurposing waste materials that would otherwise be discarded. It is a useful soil conditioner and mulch.

Mushroom compost is high in organic matter, which enhances all soils, from heavy clay to light, free-draining sand. Organic matter improves the structure and aeration of the soil, creating greater moisture-retaining and drainage capabilities. It is also a wonderful soil builder and helps keep the soil moist. It is a slow-release, organic plant fertilizer, providing low levels of lots of different nutrients to the roots of plants over time. It is especially useful for growing fruits and vegetables that thrive with a good calcium supply, such as tomatoes.

Mushroom compost should be used with caution due to its high soluble salt levels and alkalinity. These salt levels can kill germinating seeds, harm young seedlings, and cause damage to salt-sensitive plants, like azaleas and rhododendrons. It should not be used with ericaceous plants, which thrive in acidic soils. To temper the alkaline levels of mushroom compost, consider using aglime.

To get the greatest results when organic gardening with mushroom compost, thoroughly mix it in with the garden soil prior to planting. It should be used sparingly and as soil improvement, rather than as a growing medium by itself. It can be used as a 5cm deep mulch on your vegetable beds and allotment, but not on soft fruit, such as blueberries, raspberries and currants, which need neutral to acidic conditions.

Buying

Mushroom compost can be purchased in bags or in bulk and is often sold under the name 'spent mushroom compost' or 'spent mushroom substrate'. It is a by-product of the edible mushroom industry and is generated by growing mushrooms. Mushroom compost is a useful soil conditioner and mulch but may contain peat, which is no longer recommended for horticultural use due to the damage it causes to peatland ecosystems. It is also high in soluble salt, which can kill germinating seeds, harm young seedlings, and damage salt-sensitive plants. Therefore, it is important to mix mushroom compost with soil and not use it alone to grow plants. The recommended ratio is one part compost to two parts soil. You can also buy soil that is pre-mixed with mushroom compost already added, which can be used as it is, with no additional mixing needed.

When buying mushroom compost, it is important to consider its pH level. Most types of mushroom compost have a neutral pH level, but some types are made using chalk, which makes them more alkaline. If you are unsure of the pH level of your mushroom compost, you can use a pH test to find out. Mushroom compost with high alkalinity should be avoided for neutral, alkaline, or chalky soils, as it will make them excessively alkaline. It is most useful on acid soils that are low in organic matter, where the liming effect of the chalk is beneficial.

If you buy mushroom compost that is still fresh, it needs curing before you add it to your soil. Purchase fresh material in fall, winter, or early spring to give it ample time to sit and cure. Aged, cured mushroom compost can be applied any time in the spring or summer. Application is most effective when the soil is fairly dry, which avoids compacting the soil while tilling in amendments.

Mushroom compost is a great addition to your gardening efforts. It is a wonderful soil builder and helps keep the soil moist. It is high in organic matter, which enhances all soils, from heavy clay to light, free-draining sand. It also increases the water-holding capacity of the soil, which decreases the need for watering. It is suitable for most garden plants and supports various types of plant growth, from fruits and vegetables to herbs and flowers.

Frequently asked questions