Key Features
- Easy to spread
- Improves the physical structure of soil
- Adds organic material to soil
- Very economical
- Pasteurised
Product Composition
- Mid-brown in colour
- Blended agricultural straw and animal manure
Mushroom compost is a rich soil improver made from composted agricultural straw and rotted manure. Pasteurised for easy crumbling and spreading, it delivers a mid-brown colour with a pleasing earthy texture that darkens naturally as it breaks down. Perfect for:
- vegetable patches and raised beds
- improving heavy clay soils
- mulching borders and flower beds
- conditioning nutrient-poor garden soil
- boosting overall soil structure and worm activity
High in organic matter (around 66%), it enhances drainage in clay while retaining moisture in sandy soils, promotes healthy plant growth, and acts as an effective weed suppressor when used as a mulch. A natural recycled by-product, it’s an economical choice for low-maintenance, thriving gardens and rejuvenating your soil into productive, vibrant ground.
Mushroom Compost is a nutrient-dense material that works best when blended with soil prior to planting. It is not advised for use in pots, for sowing seeds, with young plants, or as a standalone growing medium. For those purposes, Multipurpose Compost or John Innes is suggested instead.
Mushroom Compost
Price range: £117.00 through £197.00 inc. VAT
Topsoil Calculator
Tap a job to fill the depth in. For a raised bed, use the depth of the bed, usually 200 to 300mm.
| Quantity | Bulk Bag (approx. 1000L), 10 x 75L Bags, 20 x 75L Bags, 30 x 75L Bags, 40 x 75L Bags |
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Specifications, Inspirational Ideas & DIY Guides
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Why Professionals & Homeowners Choose, Applications, DIY Guides & Inspirational Ideas, Maintenance, Purchasing Tips, FAQs, Related Products
Overview
Mushroom compost is the improver I reached for most often for a heavy clay border, and is the bag I get asked about more than any other in the compost range. It is the spent growing bed from a mushroom farm: wheat straw and manure composted down, cropped for a few weeks, then steamed. What arrives is mid-brown and crumbly with a little straw fibre still showing, near black when wet, and around 66% organic matter. It suits vegetable plots, raised beds and any border on clay or thin sandy ground. It’s the wrong choice around acid-loving plants because it carries chalk from the growing process. We sell it in a 1,000-litre bulk bag and in 75-litre bags from ten to forty at a time, and here is why the trade and the home gardener keep ordering it.
Why Professionals & Homeowners Choose Mushroom Compost
Six reasons come up again and again, with one of them being a warning:
- It’s pasteurised at the end of the mushroom crop, which kills weed seed and lets it go straight onto a bed.
- It is high in organic matter, so a 5cm layer forked into clay opens the structure and the worms take the rest down over winter.
- On sandy soil it works the other way round, holding water where the ground would otherwise lose it.
- It’s gentle on roots. Fresh manure can scorch; a spent mushroom bed has already been through its hot stage.
- A bulk bag dresses roughly 20 square metres, which is the cheapest way I know to get organic matter across a whole plot.
- The chalk is the catch. It nudges pH up a little every year you use it, so alternate it with horse manure or garden compost on beds that get an annual dressing.
Mushroom Compost Applications
Mushroom compost belongs with the plants that like a bit of lime: cabbage, kale and broccoli (all Brassica oleracea), where the chalk helps hold off club root, tomatoes (Solanum lycopersicum), lilac (Syringa vulgaris) and clematis. Keep it away from rhododendron, camellia, Pieris, heather (Calluna vulgaris) and blueberry (Vaccinium corymbosum), and off ground that is already chalky. It is not a seed or potting compost on its own.
- Vegetable patches and raised beds, forked in at 5cm in autumn or spring.
- Heavy clay, where I mix it with a 4 to 6cm layer of grit into the top 15 to 20cm in autumn, then let frost do the rest by freezing and splitting the clods to break them up.
- Light sandy soil that dries out every summer, dug in over winter and mulched in late February before the ground dries.
- Tired old borders and the compacted clay under a new-build lawn, once the compaction itself has been broken up.
- A 2.5 to 5cm mulch on established borders, capped with bark where weeds are the problem, since compost alone is the weakest mulch at holding them down.
DIY Guides & Inspirational Ideas
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Mushroom Compost Maintenance
Mushroom compost is a once-a-year job. On clay I put it on in autumn at 5cm. On sand I prefer to wait until late winter so the moisture it holds is there for spring growth. As a mulch it breaks down into the soil within a season, so top it up rather than piling another 10cm on, and never spread it on ground sitting in water. If you dress the same bed every year, test the pH every two years with a garden-centre kit. Anything past 7.5 should get manure the following autumn instead.
Purchasing Tips
Work the quantity out at 5cm, which is 50 litres per square metre. A 1,000-litre bulk bag covers roughly 20 square metres, a 75-litre bag about 1.5 square metres, and ten bags do a 15 square metre plot. In pots, mix one part mushroom compost with three parts topsoil or multi purpose compost, never neat.
For acid-loving plants, order our Ericaceous Compost at pH 4 to 5 instead. For a bed that wants feeding more than structure, our Horse Manure Compost is the richer bag, and if you want a finer, peat-free conditioner with no straw in it, our Green Compost is screened to 10mm and PAS 100 certified. The full range is under Compost & Soil Conditioners.
If you would rather talk your mushroom compost order through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.
Mushroom Compost FAQs
What is mushroom compost made of?
Mushroom compost is the spent growing bed from a mushroom farm: composted wheat straw and horse or poultry manure with gypsum, often under a thin casing layer of peat and chalk, cropped and then steamed before sale.
Is mushroom compost acidic or alkaline?
Mushroom compost tests near neutral to mildly alkaline, typically pH 6.5 to 7.5, but the chalk in it acts as a slow lime, so repeated yearly use pushes a bed further alkaline.
Can I use mushroom compost on rhododendrons, camellias or blueberries?
Mushroom compost is the wrong improver for rhododendrons, camellias, heathers and blueberries, because its chalk lifts the pH those plants need kept between 4 and 5.5.
How much mushroom compost do I need?
Mushroom compost goes on at 5cm, which is 50 litres per square metre. A 1,000-litre bulk bag covers roughly 20 square metres and a 75-litre bag about 1.5 square metres.
Is mushroom compost weed-free?
Mushroom compost is weed-free as sold because the growing rooms are steamed at 65 to 70°C for at least eight hours at the end of the crop, which kills weed seed along with the mushroom pests.
Can I grow vegetables straight in mushroom compost?
Mushroom compost is too salty and too limy on its own for seedlings, so fork it into the bed at 5cm a fortnight before sowing rather than planting straight into a layer of it.
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