In article ,
Roger Tonkin wrote:
Bit confused about Nicks comment on "soilless" compost. I used
a standard garden centre product Levington Potting compost with
added John Innes, what ever that may mean,
Er, did it SERIOUSLY say that? If so, God alone knows what it means,
because the marketdroids that wrote that text assuredly didn't.
John Innes compost is a class of composts, made mostly from 'soil'
(including sand and some clay). Soilless composts are made from
(traditionally) peat and (mostly nowadays) coir etc. The difference
I was referring to is that clay holds mineral nutrients far better
than the soilless material does, which is why soils without it need
so much humus (which also holds them).
The executive summary is that plants in pots run out of nutrients
more thoroughly in soilless than John Innes composts, so need them