John Innes sounds like a trade name, but it's not, it's a type of compost:
John Innes Potting Compost
JI #1 Base
7
parts sterilized loam
3 parts peat
2 parts sand or grit
Fertilizer: 4 oz / 8 gallons (3 grams / liter)
Lime or chalk: 3/4 oz / 8 gallons ( 0.5 grams / liter)
JI #2 Base: Same as 1 but double the Fertilizer and chalk
JI #3 Base: Same as 1 but
triple the Fertilizer and chalk
JI Seed compost: The fresher the sterilization, the better the germination
2 parts sterilized loam
1 part moss peat
1 part
sharp sand
The loam and peat is put through in 3/8 in (9mm) sieve.
To each bushel or 8gal(36 L) is added:
1-2 oz (42gm) superphosphate
1/2 oz
Potassium nitrate
4-6 oz (21gm) ground limestone
Ericaceous Mix: Use the base but leave out the Lime
Soilless: 3 parts peat and 1 part sand
Potting Compost: (same as above)
7 parts sterilized loam
3 parts moss peat
2 parts sharp sand
The loam and peat is put through a 3/8 in (9mm) sieve.
To each bushel (8gal/36l) is added
3/4oz (21gm) ground limestone
4oz (110gm) 14-14-14 Osmocote
This makes John Innes Potting Compost No. 1.
For a richer mix simply double the quantity of
John Innes Base to make No. 2 or treble it to
make No.3
You can make your own.