A Beginner’s Guide To Mushroom Compost

Last Updated May 14, 2021 By Bella Zinti

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Mushroom compost— made from the leftover soil used by mushroom growers— is a powerful soil additive that improves soil quality, increases water retention, and supports healthy plant growth. The nutrient-rich soil amendment is a useful alternative for organic gardenings looking to improve their garden soil, grow healthy plants, and enjoy larger harvests from their vegetable garden without using fertilizers that contain harmful chemicals and synthetic fillers.

Whether you're new to the world of organic gardening or you've got a seasoned green thumb, it's crucial to understand that mushroom compost must be used with caution. Use too much, and you risk harming your plants and ruining your hard work in the garden. Because it's high in nutrients and soluble salts, it can kill germinating seeds, young seedlings, and salt-sensitive plants. So to ensure your landscaping efforts go smoothly this gardening season, we're breaking down everything you need to know about mushroom soil and how to use it in your garden.

What is mushroom compost?

As the name suggests, mushroom compost is made from the soil leftover after mushroom farmers harvest their crop of mushrooms. Because the mushrooms require special growing conditions, the compost used is incredibly high in organic matter and nutrients, making it a great soil amendment to everyday garden soil.

While the ingredients of mushroom compost vary from grower to grower, most mushroom substrate contains some combination of the following: horse or chicken manure, chopped wheat straw, cottonseed meal, soybean meal, corn cobs, gypsum, water, and other natural compounds. The mixture is matured in controlled conditions for about a month to allow bacteria to grow. After the composting process, the mix is pasteurized at a high temperature to kill off any pathogens and unwanted weed seeds. The compost is then inoculated with mushroom spawn, and the growing process begins.

While some gardeners prefer to make their own mushroom compost, it's a time-consuming and tedious process. Because of its high salt levels and unstable organic materials, mushroom compost needs to be aged for a minimum of two years before using it in your garden. If you do want to attempt making your own mushroom compost, you'll need to do plenty of research to ensure you utilize the right bacteria, water source, and growing conditions for your mushrooms. Thankfully, the varieties you find in garden centers, home improvement stores, landscape supply firms, and gardening supply websites have been pre-aged and can be used immediately after purchase.

Benefits of Mushroom Compost

While mushroom compost should be used with care, it's one of the best natural fertilizer options out there. Here are a few of the many benefits of using mushroom compost in your gardens:

  • Creates Moist Conditions— Mushroom compost helps keep the soil moist and improves water infiltration and holding capacity. Adding the material to your soil can help to decrease your watering frequency and keep your plants from drying out during hot summer weather.
  • Improves Soil Quality— The high salt levels and wide range of nutrients in mushroom soil helps to break down dense clay to allow for improved permeability and aeration. As a result, you'll enjoy improved soil structure and healthy, happy plants.
  • Contains No Pests or Weed Seeds— Thanks to the high temperatures required during composting and pasteurization, mushroom compost is free from weed seeds and other unwanted pests that frequent your compost pile.
  • Natural and Chemical Free— Unlike traditional fertilizers, mushroom compost products are almost always made using an all-natural process and organic material, making it a safe choice for both your health and the environment. They're a great alternative to chemicals and unnatural fertilizer fillers.

Mushroom Compost vs. Traditional Fertilizer and Other Compost

Mushroom compost is typically more expensive than traditional compost, but it provides additional benefits that are well worth the added costs. The nutrients are released at a slow, natural rate that allows plants to absorb them better than traditional mineral fertilizer. Additionally, mushroom compost contains higher nutrient levels than peat moss, plain animal manure, or the leftover compost in your backyard bin.

If you're concerned about potentially harming your plants with the high sodium levels of mushroom compost, stick to other natural soil additives like animal manure, fish meal, soybean meal, or plain compost instead to add the phosphate, nitrogen, potassium, magnesium, and sulfur needed for healthy growth.

Gardening Tips on How to Use Mushroom Compost

Because mushroom growth requires such unique conditions, mushroom compost should be used with caution and careful attention. Its high sodium levels and nutrient content can harm salt-sensitive plants like rhododendrons, azaleas, camellias, and other plants in the heath family. Additionally, these nutrients can be damaging for a sensitive young plant or seedling and should only be used on those that are mature and fully grown.

Spent mushroom compost is a great addition to flower beds, vegetable gardens, and container gardening. While you can thoroughly mix a small amount into the ground right before planting, it's best to mix the soils a few months in advance to allow the pH to balance and the compost to fully blend into the soil before you start gardening. The compost can also be sprinkled on top of your garden beds like mulch.

Additionally, mushroom compost can be used to supplement growing conditions in containers. To avoid overpowering your plants, spent mushroom compost should make up around 1/4 of the total volume of the soil in the container.

The Best Mushroom Compost

Cedar Grove Organic Compost

Cedar Grove's Organic Compost is made in the Pacific Northwest from all-natural organic materials like leftover garden pruning and vegetable trimmings. It has a deep brown color and is rich in organic matter, microbes, and trace minerals. Thanks to its high nutrient content, it's ideal for using as mulch or stirring into your vegetable garden to improve moisture control.

Permagreen PRO Mushroom Compost Blend

Permagreen PRO Mushroom Compost Blend

This Permagreen PRO Mushroom Compost Blend is an affordable option that's suitable for any garden. It's made from a blend of nutrient-packed compost from mushroom growers but contains no offensive odors or synthetic materials. The 100% organic product satisfies all your natural gardening demands without requiring a laborious compost process.

Garick Organic Valley Mushroom Compost

This large, 40-pound bag of organic mushroom compost from Garick is large enough to cover all your beds and kickstart the growth of your vegetables, flowers, and other plants. It's a great way to improve soil quality and give your garden the vital nutrients it needs. Plus, it's free from antibiotics, synthetic hormones, and toxic pesticides.

Orchid Supply Store Black Gold Organic Mushroom Compost

Orchid Supply Store's Black Gold Organic Mushroom Compost is a great addition to any home garden or container. As the name implies, the mushroom substrate product has a dark, rich color and supplies an ample amount of nutrition to your garden plants. Gardeners can choose from compost bag sizes— eight pounds, fifteen pounds, and forty pounds— depending on their planting needs.

Gardenscape Mushroom Compost

Gardenscape's Organic Soil Conditioner is made from the leftover materials used to plant and grow mushrooms on an organic farm. It contains just the right balance of slow-release nutrition to improve the quality and holding capacity of clay and sandy soil. In return, you can enjoy gardening in a yard filled with happier, healthier flowers, lawns, trees, and shrubs— all without needing harsh chemicals or synthetic fertilizers.

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About the author

Bella has a Bachelors degree in interior design, is a master gardener. She designs nourishing outdoor & indoor spaces guided by the practice of Feng Shui.