Allotment Diary : Preparing this years Giant Onion Growing Mixture

Time to prepare the growing media for this years giant onions. These will be grown in 60 litre pots so I need to prepare about 360 litres in order to plant just 6 out. I'm using the same as last year which consists of 2parts Jacks Magic 1 part John innes no2 and a little perlite. The only fertiliser I add is 2 oz of 6 month slow release Gro Sure fertiliser. Other additions are 4 oz Nutrimate to add extra humus, 4 oz Calcified Seaweed for trace elements and to add a bit of lime, 1 oz Dolomite lime for extra magnesium and a handful of Rockdust. All mixed thoroughly in the cement mixer and that's it.