Re: What is the best compost to buy for 2012?
Posted: Sat Jun 16, 2012 3:42 pm
I have just about stopped assuming there is any food in bought in potting compost, it seems the simplest approach to me.
When I make my own compost from soil, leaf mould and sharp sand I am usually looking for something similar to John Innes No. 2. To add fertiliser to my mixture according to the JI formulation I would have to add 2.4 Kg Hoof and Horn, 2.4 Kg Superphosphate, 1.2 Kg Potash (i.e. 6 Kg JI Base) and 0.6 Kg Lime to a cubic metre of mix. I don't mix a cubic metre at a time and I don't use these individual ingredients. JI Base has an NPK content of approximately 5.2:7.7:10. Readily available Fish, Blood and Bone (FBB) is approximately 5:5:6.5 so it is not too different. Twenty 5" pots hold approximately 25 litres so require 150 gm JI Base and 15 gm of Lime so these are easier figures for adding fertiliser.
So what do I do in practice? Usually measure out ten 5" pots of compost and add 75 gm of FBB (I've drawn a line on a scoop). If I'm using it for Brassicas I add the Lime but otherwise don't bother. If I'm in a fussy mood, for Brassicas I might add extra Phosphate and for Tomatoes, Peppers or Aubergines I might add a bit extra Potash.
Going back to my first sentence, if I am using bought in compost I add the same amount of FBB etc. to be sure there is sufficient food to keep things going for a while. Could be more scientific but it seems to work.
When I make my own compost from soil, leaf mould and sharp sand I am usually looking for something similar to John Innes No. 2. To add fertiliser to my mixture according to the JI formulation I would have to add 2.4 Kg Hoof and Horn, 2.4 Kg Superphosphate, 1.2 Kg Potash (i.e. 6 Kg JI Base) and 0.6 Kg Lime to a cubic metre of mix. I don't mix a cubic metre at a time and I don't use these individual ingredients. JI Base has an NPK content of approximately 5.2:7.7:10. Readily available Fish, Blood and Bone (FBB) is approximately 5:5:6.5 so it is not too different. Twenty 5" pots hold approximately 25 litres so require 150 gm JI Base and 15 gm of Lime so these are easier figures for adding fertiliser.
So what do I do in practice? Usually measure out ten 5" pots of compost and add 75 gm of FBB (I've drawn a line on a scoop). If I'm using it for Brassicas I add the Lime but otherwise don't bother. If I'm in a fussy mood, for Brassicas I might add extra Phosphate and for Tomatoes, Peppers or Aubergines I might add a bit extra Potash.
Going back to my first sentence, if I am using bought in compost I add the same amount of FBB etc. to be sure there is sufficient food to keep things going for a while. Could be more scientific but it seems to work.