Compost Range Explained and Compared
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Multi Purpose Compost is the all-rounder for seeds, pots and raised beds, Ericaceous Compost at pH 4 to 5 is for acid-loving plants, and John Innes No.3 is the loam-based mix for shrubs and trees in permanent pots.
Multi Purpose is my pick if you are not sure which to buy. It handles seeds, pots and raised beds, with the feed already in the mix.
pH 5.5 to 6.5 · NPK 12-12-17 · Feeds for 3 to 4 months
Ericaceous is the peat-free, option for acid-lovers like blueberries and rhododendrons, especially on chalky ground.
pH 4 to 5 · Peat free · For acid-loving plants
John Innes No.3 is the one to put a tree or a big shrub into. The loam gives it weight, so it holds its structure for years, not months.
55% loam · pH 6.0 to 6.5 · Great drainage
| Multi Purpose Compost | Ericaceous Compost | John Innes No.3 Compost | |
|---|---|---|---|
| What it is made of | Peat, composted bark fines and wood fines | Peat-free mix | 55% sterilised loam, 25% peat, 17% sharp sand, ground limestone |
| Peat free | No | Yes | No |
| pH | 5.5 to 6.5 | 4 to 5 | 6.0 to 6.5 |
| Feed | NPK 12-12-17 at 1kg per cubic metre, lasting 3 to 4 months | Balanced, lasting 3 to 4 months | Superphosphate and potassium sulphate, three times the base feed of No.1 |
| Bag sizes | 700, 1,000 and 1,200 litre bulk bags, or 50 litre bags | 700, 1,000 and 1,200 litre bulk bags, or 70 litre bags | 700 litre builders bag, or 25 litre bags |
| Best for | Seeds, cuttings, potting on, raised beds | Rhododendrons, camellias, blueberries, acers | Trees, shrubs and climbers in large permanent containers |
| Not for | Acid-loving plants | Anything that wants lime | Seed sowing |
| Buy | Multi Purpose sizes and prices | Ericaceous sizes and prices | John Innes No.3 sizes and prices |
Why Professionals & Homeowners Choose Our Composts
Buying compost in bulk means committing to one grade for the whole job, so the choice matters more than it does when you are picking up a single bag off a forecourt. Match it to what you are growing, and to how long the plant stays in its pot. Get that wrong on a raised bed and you are living with it all season.
- Enough compost arrives in one delivery to fill a whole raised bed or a run of planters, instead of a car boot full of split bags.
- Multi Purpose and John Innes No.3 are both heat treated, so no weed seedlings and no fungus gnats come out of the bag.
- The feed is already in the mix, at three to four months of fertiliser in Multi Purpose and three times the base feed of No.1 in John Innes No.3.
- Ericaceous Compost sits at pH 4 to 5 for the acid lovers, which most bulk suppliers do not carry at all.
Multi Purpose, Ericaceous and John Innes No.3 Compost in Detail
Multi Purpose Compost
Multi Purpose Compost is the all-rounder, made from peat with composted bark fines and wood fines, a lime-based wetting agent so it takes water again after drying out, and a 3 to 4 month NPK 12-12-17 feed already in it. pH sits at 5.5 to 6.5.
- Suits seeds, cuttings, potting on, hanging baskets, raised beds and general planting.
- Sterilised, so no weed seeds or diseases.
- Holds moisture and drains freely – great for young roots.
- Feeds for 3 to 4 months, then liquid feed from there.
- Made with responsibly sourced peat.
Ericaceous Compost
Ericaceous Compost is the one for plants that cannot cope with lime. It is a peat-free mix at pH 4 to 5, fine and consistent, and the only practical way to grow blueberries or rhododendrons well if your ground is chalky or limy.
- pH 4 to 5 keeps iron and manganese available, which is what stops the yellow leaves on acid lovers.
- Rhododendrons, azaleas, camellias, heathers, blueberries, Japanese maples and magnolias.
- Fine, even texture that packs around roots in a container without leaving air pockets.
- Keep it away from anything that likes lime. Lavender, clematis and brassicas will sulk in it.
- Water it with rainwater where you can. Tap water in a hard water area slowly pushes the pH back up.
John Innes No.3
John Innes No.3 is the traditional loam-based compost, and the only one of the three to put a tree or a big shrub into. It is 55% sterilised loam, 25% peat, 17% sharp sand and ground limestone, with superphosphate and potassium sulphate for feed, and it sits at pH 6.0 to 6.5.
- Loam gives it weight, so a tall container stays upright and the mix does not slump after a season.
- All three John Innes grades sit on the same soil base and differ by how much base fertiliser goes in: No.1 gets one dose, No.2 twice, No.3 three times.
- Suits established shrubs, trees, climbers, fruit bushes, tomatoes and anything in a large permanent container.
- The sand keeps it draining, which peat-only mixes lose as they age.
- Too rich for seed sowing. Start seeds in Multi Purpose and pot on into No.3.
Applications
Match the compost to how long the plant stays put. Anything you sow, prick out or pot on this year goes in Multi Purpose. Anything living in its container beyond two years goes in John Innes No.3. Anything on the acid-lover list goes in Ericaceous, however long it stays. Mixing is fine, and half John Innes No.3 to half clean horticultural grit is the mix for alpines and anything that hates wet feet.
- For raised vegetable beds, fill with Multi Purpose Compost and top up each spring with a soil improver rather than more compost.
- For seed trays and cuttings, Multi Purpose Compost sieved fine is what the seed wants.
- For blueberries, rhododendrons and acers in pots, use Ericaceous Compost and use rainwater where you can.
- For trees and shrubs in large containers, John Innes No.3 holds up, repotted or top dressed every three to five years.
- For tomatoes and hungry summer crops, John Innes No.3 in the final pot takes a liquid feed from the first truss.
- For alpines and Mediterranean herbs, cut John Innes No.3 half and half with clean horticultural grit.
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How to Look After Compost in Pots and Beds
The feed in Multi Purpose and John Innes No.3 runs out after three to four months, so anything still growing in August wants a liquid feed weekly from then on. Peat and bark mixes shrink as they break down, so top raised beds up each spring with 5cm of soil improver rather than fresh compost, which is cheaper and better for the structure. Containers in John Innes No.3 get repotted or top dressed every three to five years.
What to Check Before Ordering Compost
Work out the volume in litres before you order: length by width by depth in metres, multiplied by 1,000. A 1.2m by 2.4m raised bed filled 30cm deep needs roughly 860L. Worth knowing that the three are not bagged the same, with Multi Purpose in 50 litre bags, Ericaceous in 70 and John Innes No.3 in 25, so work in litres rather than counting bags. On a deep bed, put topsoil or a soil improver in the bottom half and save the compost for the top 20cm, where the roots actually are.
Compost FAQs
What is the difference between multi purpose compost and John Innes No.3?
Multi purpose compost is a light peat and bark mix for seeds, cuttings and pots that get emptied each year, while John Innes No.3 is loam-based with sand and three times the base feed, made for plants staying in their container for years. Sow in Multi Purpose, pot on into No.3.
Can I fill a raised bed with compost?
A raised bed can be filled entirely with Multi Purpose Compost, and on a shallow bed under 30cm that is what I would do. On anything deeper, put topsoil or a soil improver in the bottom half and keep the compost for the top 20cm, because that is where the roots are and the rest is expensive filler.
Which compost do I need for blueberries and rhododendrons?
Blueberries, rhododendrons, camellias, azaleas and heathers all need Ericaceous Compost, which sits at pH 4 to 5. In an ordinary compost their leaves go yellow within a season, because the plant cannot take up iron at the wrong pH.
Which of your composts are peat-free?
Ericaceous Compost is the only peat-free option of the three. Multi Purpose is made with responsibly sourced peat, and John Innes No.3 is 25% peat by volume. For a peat-free all-rounder, RocketGro Multi Purpose Compost is the one to choose.
How long does the feed in a bag of compost last?
The feed in Multi Purpose and John Innes No.3 lasts three to four months, so anything potted in April wants a liquid feed from about August. Multi purpose composts are low in nutrients by design, so start earlier if growth looks tired.
What is the difference between John Innes No.1, No.2 and No.3?
John Innes No.1, No.2 and No.3 sit on exactly the same soil base and differ only in how much base fertiliser goes in, at one dose, two and three. The ground limestone is the same in all three, so the number tells you how much feed you are buying, not how different the mix is. No.3 is the one for mature plants in big containers.
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Ericaceous Compost
Price range: £147.00 through £404.00 inc. VAT -
Mushroom Compost
Price range: £117.00 through £197.00 inc. VAT -
Composted Bark Fines
Price range: £132.00 through £333.00 inc. VAT -
Horse Manure Compost
Price range: £117.00 through £242.00 inc. VAT
