Free delivery on all orders over £100
Mushroom Compost has become very popular with gardeners over the last few years, mainly due to the high concentration of organic matter it contains. However we are increasingly finding that its benefits, and the best way to use it are causing some confusion amongst people, so this post aims to help you understand exactly what mushroom compost is, and how you can use it to benefit your garden.
The vast majority of mushroom compost sold in the UK is actually spent mushroom compost, which has already had mushrooms grown in it. Due to the decline of small scale mushroom farms it is harder to get hold of now than it was 40 years ago, when it was considered a waste product, but it can be well worth the effort.
What Is Mushroom Compost?
This compost is a mix of straw, corn cobs, horse and poultry manure, peat moss, chalk and lime. This creates a product that is very high in organic matter and is perfect for mushroom farming.
The compost will be laid out in beds and mushroom spores injected into it to start growth. A full mushroom growing cycle is normally around 3 weeks before harvest.
The used compost is then heat treated to remove any pests or weeds before being reused. Typically each batch of compost is used for 2 or 3 cycles before being swapped out for fresh. This is due to the amount of nitrogen depletion that the mushrooms create. It is then recycled as an organic mushroom compost for use in both private and commercial gardens.
Benefits of mushroom compost
Although it can be used for a wide range of different applications the main benefit of mushroom compost in our experience is to improve water retention in soils. Due to the straw content mushroom compost has a very high level of water retention, which is especially good for plants that like to have their roots kept in moist conditions, like ferns.
The compost’s ability to retain water for longer than standard compost means that you won’t have to water your plants as frequently, possibly by as much as 50%. This benefits you both in time and in ecological savings of reduced water use.
Spent mushroom compost is a by-product of the mushroom farming industry. This means that it requires no additional resources to produce it, reducing its ecological impact, whilst simultaneously ensuring that it does not go to waste once its main purpose has been fulfilled.
Breaks down clay soils
Possibly the biggest benefit of mushroom compost is how effective it is at breaking down clay soil and turning it into a useable medium. The amount of compost required will vary depending on the density of the clay, but a good starting point is to dig 2-3" of compost to 1 spades depth for open areas or around 35% compost to 65% clay for beds.
Mild Nitrogen Content
Mushroom compost has a low nitrogen content because much of the nitrogen in the compost will have been utilized by the mushrooms that were originally grown in it. While a low nutrient level might sound like a poor idea, it actually can be very beneficial. The low level of nitrogen will provide a slow intake of nutrients for your plants, without encouraging weeds to grow. Fertilizers that have high nitrogen levels do have their uses, but the problem with them is that they can cause too much leafy growth at the expense of flowers and fruits, and they also result in the production of weeds because nitrogen gives them a huge boost. Compost such as mushroom compost with low levels of nitrogen is good for the long-term health of plants.
Like most types of compost, mushroom compost provides low levels of lots of different nutrients to the roots of plants over time, as it gradually degrades. This makes it great as a slow-release fertilizer, feeding the soil and therefore improving plant health.
High in Calcium
Mushroom compost has high calcium levels, which makes it especially useful for growing fruits and vegetables that thrive with a good calcium supply. This type of compost would be especially beneficial for growing tomatoes, as tomatoes often suffer from a blossom end rot as a result of having too little calcium available in their soil.
Mushroom compost works as an effective mulch when several inches are added on top of the soil, acting as a layer of insulation. It will help to keep plant roots cool in the summer and warm in the winter, and it will help to prevent moisture from evaporating. By adding mushroom compost as a mulch to top-dress soil, the nutrients will gradually filter down into the soil as you water the plants, or when rain carries the nutrients down into the layers beneath.
Worms love moist soils, and as mushroom compost improves water retention, it makes it especially attractive to worms. Having soil that encourages earthworms to set up home in your garden is beneficial to your plants, as worms improve soil structure, improve drainage, and allow roots to be able to extract nutrients from the soil more effectively.
Drawbacks of mushroom compost
Due to the presence of lime and chalk in the compost it will tend to be slightly alkaline. Although this will not cause any issues in the cultivation of normal plants if you are trying to grow anything that is particularly acid loving then our 20mm mulching compost would be a better choice.
The other drawback of mushroom compost is linked to its biggest advantage, moisture retention. If too great a density of compost is added to an area then it can lead to water logging, which in turn damages plant roots. To combat this it is best to build the level of compost in the soil over several seasons.