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Adding compost to a container

What is John Innes compost?

Published: Thursday, 7 April, 2022 at 8:17 am

All you need to know about John Innes compost, in our guide.

What is John Innes compost?

John Innes refers to the compost type and is not a compost manufacturer. The range of John Innes composts were originally developed in the 1930’s at the John Innes Horticultural Research Institute, named after the 19th century developer and philanthropist, John Innes, who bequeathed his fortune to the improvement of horticulture. John Innes composts are made by a number of different compost brands, and are ideal for long-term plant growth in pots and containers.

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How does John Innes differ from other composts?

John Innes composts weigh much more than other types of potting compost as the key ingredient is loam, or soil, along with peat or peat substitute, sand, and fertilizer. Loam used in compost is usually made of a mix of sand, silt, and clay, and is sterilised to kill weed seeds, pests, and diseases.

The advantage of loam is that it provides a steady supply of nutrients and water, is free draining, with good structure and aeration. This good absorption and release of water and nutrients is sometimes referred to as having a high level of “buffering”.

These qualities make John Innes composts ideal for long-lived plants kept in containers for more than one growing season. Also, young plants growing in loam-based compost often adapt more readily to garden conditions, when planted into the ground.

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What are the different types of John Innes composts?

Top-dressing a potted shrub with John Innes compost

There are three types of John Innes potting compost: John Innes No 1, John Innes No 2, and John Innes No 3. These numbers refer to the varying levels of fertilizer included in the mix, to suit different uses. There's also John Innes compost for seed and cuttings, as well as an ericaceous compost which is lime-free and suitable for acid-loving (lime-hating) plants including blueberry, rhododendron, azalea, camellia, and pieris.

John Innes No 1 is designed for pricking out or potting on young seedlings or rooted cuttings. It contains a low, carefully balanced amount of fertilizer to give enough for growth but avoid scorching the delicate young roots.

John Innes No 2 contains moderate levels of fertilizer and is used for potting on plants at the next stage of growth, and most vegetables.

John Innes No 3 contains the highest levels of fertilizer and is suitable for mature plants growing in pots, such as shrubs, small trees, perennials, and conifers.

Are John Innes composts peat free?

Using peat-free John Innes compost to fill a pot
Using peat-free John Innes compost to fill a pot
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The traditional recipe for John Innes composts uses peat, although there are now some that are made using peat substitutes.

Advice on buying John Innes composts

  • The quality of composts on sale may vary and there are no legally binding quality control standards for John Innes composts
  • However, many manufacturers belong to the John Innes Manufacturers’ Association and aim to produce good quality products and this will be clearly indicated on the compost bag
  • While peat-free John Innes mixes are harder to find, it's worth seeking them out as use of peat is hugely damaging to the environment and exacerbates climate change 

Where to buy peat-free John Innes composts

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