Soil Improver Range Explained and Compared
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Our soil improver all do their own specific jobs. Green Compost is the cheap bulk option, Mushroom Compost changes heavy clay fastest, Horse Manure Compost feeds hungry crops, and Composted Bark Fines is safe around acid-loving plants.
Green Compost is my pick for improving a whole garden on a budget. It is the cheapest way to add bulk organic matter.
0 to 10mm · pH 8 to 8.5 · PAS100 certified
Mushroom Compost is the one for heavy clay. It works fastest, but keep it away from acid-loving plants.
Around 66% organic matter · Pasteurised · Weed free
Horse Manure Compost is the one with real feed in it. Roses and hungry vegetables love it.
Natural NPK feed · Low odour · Weed free
Composted Bark Fines give the dark decorative finish. They are also the only acid-safe option of the four.
8mm · Spruce and conifer · Weed suppressing
| Green Compost | Mushroom Compost | Horse Manure Compost | Composted Bark Fines | |
|---|---|---|---|---|
| Nutrient level | Low, released slowly | Medium | High, NPK around 0.7-0.3-0.6 | Very low |
| pH | 7.8 | 6.5 to 7.5, alkaline over repeated years | 7 to 8.5, alkaline | 5.5 to 6.5, slightly acidic |
| Texture and grade | Fine, screened 0 to 10mm | Crumbly, mid-brown, pasteurised | Dark, crumbly, low odour | Fine, screened to 8mm, dark |
| How to use it | Spread 5 to 7.5cm on top, or fork 5cm into new ground | Fork 5cm in, then top up 5cm each autumn | Mulch at 5 to 7.5cm, or top dress in autumn | Spread 5 to 7.5cm on top only |
| Best for | Bulk conditioning, no-dig beds, whole borders | Heavy clay, sandy soil, brassica and veg beds | Roses, fruit bushes, hungry vegetables | Ornamental borders, acid-loving plants, a dark finish |
| Not for | Potting, seed sowing, growing medium | Rhododendrons, camellias, heathers, blueberries | Potting, seed sowing, acid lovers | Seed sowing, digging in as a feed |
| Price | Price range: £100.00 through £194.00 inc. VAT | Price range: £117.00 through £197.00 inc. VAT | Price range: £117.00 through £242.00 inc. VAT | Price range: £132.00 through £333.00 inc. VAT |
| Choose bag size | Choose bag size | Choose bag size | Choose bag size |
Over my 15 years working with these materials, I used all four of these on clay borders, tired shrub beds and vegetable plots, and they are not interchangeable. Green Compost is the one I would buy by the tonne to do a whole garden. Mushroom Compost is what I reached for on heavy clay. Horse Manure Compost is the one with real feed in it. Composted Bark Fines is the dark decorative finish, and the only one of the four I would put near an acid lover. Below is what each one is good at.
Why Professionals & Homeowners Choose Our Soil Improvers
Heavy clay, tired borders and a raised bed that has given three seasons of veg all want the same thing, which is organic matter by the barrow load. What separates these four is how much feed comes with it, which way the pH leans, and whether you are spreading it on top or forking it in. Get that right and a border that was a bathtub over winter crumbles in your hand by the second summer. None of these are a soil so they won’t will fill a bed or level ground. Topsoil versus compost sets out which material does which job.
- All four add organic matter that opens clay and holds water in sand, and the difference in the way the soil works shows after about two seasons.
- All four are heat treated or composted hot enough to kill weed seed, so the improver does not bring a fresh crop of weeds in with it.
- Horse Manure and Mushroom Compost bring nutrients with them, while Green Compost and Bark Fines stay gentle enough for established planting.
- Composted Bark Fines sits at pH 5.5 to 6.5, which makes it the one to use around rhododendrons, blueberries and acers.
Product Comparison of Our Soil Improver Range
Green Compost
The workhorse of the four, and the one I buy by the tonne for a whole garden. Peat-free, PAS 100 recycled green waste, screened to 0 to 10mm.
- Opens up clay and holds water in sand, cheaper at scale than anything else here.
- Feeds slowly rather than hard, which suits established borders and shrubs.
- Heat treated above 60°C and tested, so no weeds come up out of the bag.
- Spread 5 to 7.5cm on beds, or fork 5cm into the top spit of new ground.
- Not for pots or seeds, and it can carry trace plastic from recycling.
Mushroom Compost
My first choice for clay vegetable beds, and I still rate it above anything else there. Pasteurised straw and manure, mid-brown and crumbly.
- At around 66% organic matter, it shifts heavy clay faster than green compost.
- Works the other way too, bulking up thin sandy soil that will not hold water.
- Pasteurised, so no weed seed to hand pull from your veg beds all summer.
- The lime in it suits brassicas, which want the pH up.
- Keep it away from rhododendrons, camellias, heathers and blueberries.
- Fork 5cm into a new bed, or lay 5cm on top each autumn for the worms.
Horse Manure Compost
The richest feed of the four, and why rose growers have sworn by it for years. Fully composted stable litter, dark, crumbly and low odour.
- Adds feed as well as organic matter, so it suits roses, fruit and hungry crops.
- Well rotted, so it will not scorch roots the way fresh manure does.
- Heat treated, so it arrives weed free and without the stable smell.
- Top dress in autumn, or mulch 5 to 7.5cm in spring, kept clear of stems.
- Not for pots or sowing, and it leans alkaline, so keep it off acid lovers.
Composted Bark Fines
A fine mulch that doubles as a soil improver, made from composted spruce and conifer. At pH 5.5 to 6.5, it is the only one I would use near acid lovers.
- A dense 5 to 7.5cm layer lets rain through and keeps weeds down.
- Conditions heavy clay well, though more slowly than mushroom compost.
- Holds moisture but still drains, which suits moisture-loving perennials.
- Light, easy to spread evenly, and dark enough to make planting stand out.
Applications
For feed, go manure or mushroom. For bulk at the lowest price, go green compost. Where the border is on show or the plants hate lime, go bark fines. Keep all four off steep banks and waterlogged ground.
- On heavy clay, fork Mushroom Compost in at 5cm, then mulch the surface each autumn.
- Horse Manure Compost suits hungry veg, but go light on carrots, parsnips and onions.
- For no-dig, lay Green Compost 5 to 7.5cm over cardboard and plant straight in.
- On rose and fruit borders, mulch with Horse Manure Compost in spring, off the stems.
- Near rhododendrons, camellias, blueberries and acers, use Composted Bark Fines.
- Round a new tree, any of the four works as a ring, but never in the planting hole.
Inspirational Ideas & DIY Guides
How I quickly determine the type of soil I’m working with.
Jen
How I identify garden soils that need improving or removing.
Ben Parrot
The 3 components of soil, how to test them, and what I look for when choosing the best top soil.
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Maintenance
A soil improver is a yearly habit rather than a one-off job. Lay 5cm on the surface each autumn and let the worms pull it down over winter, which saves you the digging and does the soil structure less harm than turning it over. On heavy clay, autumn is the right time. On light sandy or chalky ground, hold off until late winter and get it down before the soil dries out, so the moisture is there when growth starts. Expect a surface layer to have largely vanished into the soil within 12 months, which is exactly what you want from it.
Purchasing Tips
Work out which job you are doing first, because the two need very different quantities. Spreading it on the surface as a mulch at 7.5cm takes 75 litres per square metre. Forking it into the ground as an improver takes 25 to 40 litres per square metre, which is roughly half as much material for the same bed. Then check the litres on the bag size you pick, because this range is not consistent: the Mushroom Compost bulk bag holds 1,000 litres and the Horse Manure builders bag is nearer 600. Buy the whole job in one delivery, because batches vary a little in colour and texture and a top-up rarely matches. If you cannot decide, Green Compost is the cheapest and the safe middle ground for most gardens.
FAQs
What is the difference between a soil improver and compost?
A soil improver goes on or into ground you already have, while a potting compost is a growing medium for containers. All four products on this page are improvers, and not one of them is a potting compost.
Which soil improver is best for heavy clay?
Mushroom Compost shifts heavy clay fastest of the four, because it carries the most organic matter at around 66%. Fork 5cm in the first year, then mulch every autumn and let the worms carry on the work.
Can I use a soil improver for potting or seed sowing?
Soil improvers are not potting or seed composts, and all four on this page say so on their own product pages. Seedlings want a fine, low-nutrient mix, so use Multi Purpose Compost or John Innes No.3 for pots and trays.
Which soil improver is safe around rhododendrons and blueberries?
Composted Bark Fines is the only one of these four safe around acid-loving plants, at pH 5.5 to 6.5. Mushroom Compost and Horse Manure Compost both lean alkaline, so keep them away from rhododendrons, camellias, heathers and blueberries.
How deep should I spread a soil improver?
A soil improver goes on at 5 to 7.5cm as a surface mulch, or gets forked in at 5cm when you are making new ground. Thinner than 5cm does very little, and 7.5cm is the depth to work your quantities on.
How much soil improver do I need?
Spreading a soil improver on the surface at 7.5cm takes 75 litres per square metre, so a 1,000 litre bulk bag covers roughly 13 square metres. Forking it into the ground instead takes 25 to 40 litres per square metre, so the same bag does two to three times the area.
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Horse Manure Compost
Price range: £117.00 through £242.00 inc. VAT -
Mushroom Compost
Price range: £117.00 through £197.00 inc. VAT -
RocketGro Multi Purpose Compost
Price range: £187.00 through £284.00 inc. VAT -
RocketGro Magic Mulch
Price range: £162.00 through £384.00 inc. VAT
