John innes no. 3 compost
John innes no. 3 compost - image 2
John innes no. 3 compost - image 3

John Innes No.3 brings rich, sustained nutrition to mature plants with its traditional high-fertility loam-based formula. This nutrient-dense compost combines sterilised loam, peat and sharp sand for the perfect balance of drainage and moisture retention. Perfect for:

  • established shrubs, trees and climbers
  • large containers and raised beds
  • vigorous fruits and vegetables like tomatoes
  • fruit bushes and perennials
  • long-term potting projects

The stable structure delivers essential nutrients over time, supporting strong root growth without frequent re-potting. John Innes No.3 is ideal for creating healthy, thriving displays in your garden or greenhouse, perfect for renovating your indoor and outdoor spaces.

John Innes No.3 Compost

Price range: £127.00 through £232.00 inc. VAT

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Tap a job to fill the depth in. For a raised bed, use the depth of the bed, usually 200 to 300mm.

John Innes No.3 is the richest of the three potting grades. All three sit on the same soil base and differ only in how much base fertiliser goes in: No.1 gets one dose, No.2 twice that, No.3 three times. The ground limestone stays the same across all three, so what you are buying is more feed, not a different mix. It excels with mature and established plants that need sustained, long-term nutrition – think shrubs, trees, climbers, fruit trees, vines, and even larger indoor specimens destined to stay potted for years.

Key Features

  • Great air/water balance
  • Easy to water
  • Limed to suit most plants, not for lime-haters
  • High levels of nutrients
  • Long-lasting

Product Composition

  • John Innes No. 3 compost
  • Sterilised loam, peat, sharp sand and ground limestone
  • 8mm Loam: 55% v/v
  • Peat: 25% v/v
  • Sharp sand: 17% v/v
  • Contains Super Phosphate
  • Contains Potassium Sulphate
Quantity

Builders Bag (approx. 700L), 5 x 25L Bags, 10 x 25L Bags, 15 x 25L Bags, 20 x 25L Bags, 30 x 25L Bags, 40 x 25L 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

I get asked what to put in a big pot more than almost any other container question, and John Innes No 3 is usually my answer. It is the richest of the loam-based potting composts: the same soil base as No 1 and No 2, seven parts sterilised loam to three parts peat and two parts sharp sand, with three times the base fertiliser of No 1. Ours is screened to 8mm and runs roughly 55% loam, 25% peat and 17% sharp sand, with ground limestone, superphosphate and potassium sulphate through it. It is dark, dense and properly heavy next to a bag of multi-purpose, and that weight does two jobs; holding feed and water in reserve and keeping a tall shrub upright in a gale. This is a compost for mature plants staying put for years, not for seedlings.

Why Professionals & Homeowners Choose John Innes No.3 Compost

Most of the container failures I get called out to come down to the wrong compost in a large pot, and this is the mix that fixes them.

  • The loam holds nutrients and water in reserve, so a pot does not swing between soaked and bone dry the way a soil-less mix does.
  • There is enough feed in the mix to carry an established plant through its first couple of months, so you are not liquid feeding from week one the way you are with a bag of multi-purpose.
  • The weight is a real advantage in an exposed garden, where a light compost lets a standard bay or olive go over on the first windy night.
  • Dried-out soil-less compost shrinks from the sides of the pot and the next watering runs straight through, which loam mixes do not do.
  • The recipe is fixed and public, so No 3 is the same mix wherever you buy it, although loam quality varies between suppliers and that is the thing to watch.
  • Used neat it can be stodgy, and it is too rich for seedlings and rooted cuttings, which want a seed compost or No 1 instead.

John Innes No.3 Compost Applications

John Innes No 3 is what I reach for when a plant is going into its final pot and staying there. Bay (Laurus nobilis), olive (Olea europaea), box (Buxus sempervirens), fig (Ficus carica) and agapanthus (Agapanthus africanus) all do well in it, as do tomatoes in their last container. It is limed, so it is wrong for lime-haters: blueberry (Vaccinium corymbosum), rhododendron, camellia (Camellia japonica) and pieris (Pieris japonica) want an ericaceous mix instead.

  • Final potting of shrubs, standards and small trees staying put for several years.
  • Large patio containers, where the extra weight keeps a top-heavy plant stable.
  • Final pots for hungry crops, usually tomatoes, aubergines and peppers.
  • Top-dressing established pots each spring instead of a full repot.
  • Blended mixes, with horticultural grit added for olives, alpines and succulents that want sharper drainage.

DIY Guides & Inspirational Ideas

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John Innes No.3 Compost Maintenance

Feed a pot of John Innes No 3 from around six to eight weeks after potting, once roots reach the sides, and keep it up through the growing season. Every spring, scrape the top 5cm off anything you are not repotting and replace it with fresh No 3. A 5 to 7cm topping of bark or washed gravel is worth adding too, because at that depth adult vine weevils cannot get down into the compost to lay. The catch is that you can no longer see whether the pot is moist.

Purchasing Tips

Buy John Innes No 3 by volume, not weight. A 45cm-wide pot at 40cm deep holds roughly 60 litres and a 50cm cube planter about 125 litres, so a 700 litre builders bag fills ten to twelve decent pots and five 25 litre bags do one. For a bed or trough, the calculator on our good quality topsoil guide gives the volume in litres. Loam-based compost changes in storage as the nitrogen in it mineralises, so buy what you will use this season rather than stockpiling.

If you would rather talk your John Innes No.3 compost order through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

John Innes No.3 Compost FAQs

What is John Innes No 3 compost?

John Innes No 3 is a loam-based potting compost made to a fixed public recipe: seven parts sterilised loam, three parts peat and two parts sharp sand, plus ground limestone and three times the base fertiliser used in No 1. It is the richest of the three potting grades, made for mature plants in permanent containers.

What is the difference between John Innes No 2 and No 3?

John Innes No 2 and No 3 use the same soil base and differ only in feed: No 2 carries twice the base fertiliser of No 1, No 3 three times. No 2 is the everyday potting grade, No 3 is for final potting of shrubs, trees and heavy croppers.

Can I use John Innes No 3 for seedlings?

John Innes No 3 is too rich for seedlings and rooted cuttings, which do better in a seed compost or No 1. Keep it for the final pot, once a plant is established and feeding properly.

Is John Innes No 3 suitable for blueberries and other acid-loving plants?

John Innes No 3 contains ground limestone, so it is wrong for blueberries, rhododendrons, camellias and pieris. Those need an ericaceous mix or another lime-free compost.

Is John Innes No 3 peat free?

John Innes No 3 is not peat free: peat is about a quarter of the traditional recipe and roughly 25% of this mix by volume. Retail peat sales remain legal in the UK, with the government saying it will legislate a ban when parliamentary time allows.

Can I use John Innes No 3 in a raised bed?

John Innes No 3 works well in a raised bed, but it is an expensive way to fill deep volume. I use it as the top planting layer, over topsoil where roots will not reach for a season or two.

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