On 25/03/2013 08:28, Muddymike wrote:
I've just had an email offering me

"J Arthur Bowers Multi-Purpose
Compost with added John Innes 35ltr"

What exactly are they adding extra of? I always understood John Innes to
be a formula which changed for different plantings.

Mike



Most multipurpose composts are rather light. All John Innes composts,
to my knowledge, are loam-based with grit (plus variable amounts of
feed), making them heavier. Adding JI compost to a multipurpose gives
it extra weight and substance. When used in pot culture, extra weight
is helpful as a heavier pot is less likely to blow over in windy
weather. Adding weighty drainage crocks to the bottom of the pot also
helps.

Another advantage would be using a multi with JI when preparing a bought
plant (usually in peat/multi compost) for a life in heavier soil. I
often do this with shrubs I want to grow on before planting out, so that
I have a substantial specimen plant which is already partly acclimatised
to my heavy soil.

--
Spider
from high ground in SE London
gardening on clay