Seed Compost: John Innes Mix with Oven-Sterilised Loam

The John Innes seed compost, worked out in the 1930s: 2 parts sterilised loam, 1 part peat and 1 part coarse sand by volume, with a little superphosphate and ground chalk. The RHS shows how to sterilise garden soil at home: 10 minutes at 71–79 °C in the oven, which clears out most of the soil organisms that harm or compete with seedlings. The picture: potting compost in a pot (Wikimedia Commons, CC BY-SA 2.0).