What is John Innes potting compost?
John Innes potting media, or composts, are widely sold and offer significant advantages over soil-free potting media due to the weight, trace element content and the effect of soil content in avoiding undue chemical and water fluctuations (buffering activity).
Peat is used in the original recipe, but peat substitute may also be used and is environmentally preferable. As most peat substitutes are much less acid than peat, less ground chalk is needed to raise the pH of the mix.
The currently available formulations are:
John Innes Seed Compost
This mix is used for sowing and cuttings until the seedlings are ready for pricking out or the cuttings have rooted. To mix your own (all ‘parts’ are by volume):
2 parts by loose bulk medium sterilized loam
1 part by loose bulk good peat or peat substitute
1 part by loose bulk coarse sand
To each 9-litre (2-gallon) bucket of the mixture add:
10g (1/3oz) superphosphate
5g (1 teaspoon) ground chalk
John Innes Potting Composts
a) Soil mix
7 parts by loose volume medium sterilized loam
3 parts by loose volume good peat or peat substitute
2 parts by loose volume coarse sand
b) Fertilizer mix (John Innes Base)
2 parts by weight hoof and horn meal (or 2/3 of a part by weight Nitroform*)
2 parts by weight superphosphate
1 part by weight sulphate of potash
John Innes Compost No 1
This mix is suitable for young plants. It is used for pricking out or potting-up young seedlings or rooted cuttings and short-term potting such as for bedding plants or vegetable transplants which will subsequently be planted out.
To each 9-litre (2-gallon) bucket of soil mix add:
28g (1oz) John Innes Base
5g (1 teaspoon) ground chalk
John Innes Compost No 2
This mix contains double the amount of nutrient in John Innes No 1 to suit established plants. It is suitable for most houseplants and vegetable plants in containers.
To each 9-litre (2-gallon) bucket of soil mix add:
56g (2oz) John Innes Base
10g (1/3oz) ground chalk
John Innes Compost No 3
This mix is the richest (triple the nutrients in John Innes No 1) and works well for established plants, trees, shrubs and climbers, including fruit trees, bushes and vines, and mature indoor plants which are to remain in the pots for some considerable time. No 3 Compost is also suitable for vigorously-growing plants such as tomatoes and chrysanthemums.
To each 9-litre (2-gallon) bucket of soil mix add:
84g (3oz) John Innes Base
15g ground chalk
John Innes Ericaceous Compost
A recently developed product that is suitable for use with ericaceous or ‘lime-hating’ plants.
Peat-based or peat-free media with ‘added John Innes’
Adding John Innes potting media to soil-less media is sometimes done to improve buffering, trace element content and weight of these potting media. As John Innes potting media contain many fine particles gardeners should be wary of adding John Innes materials to other media as the ‘fines’ may fill or block the air spaces within the media that are vital for drainage and aeration of the root zone. This is no doubt taken into account by manufacturers of media that is labelled as having 'added John Innes' and formulations adjusted for adequate drainage and aeration.
*Nitroform (urea formaldehyde) is available through the post from:
Garden Direct
The Garden Centre
Birchall Lane
Cole Green
Hertford
SG14 2NR
Tel. 0845 217 0788