OT? Soil vs. non-soil mixes.

Rodger Whitlock totototo@telus.net
Wed, 08 Mar 2006 13:05:32 PST
On  7 Mar 06 at 12:06, Kenneth Hixson wrote:

>          To the best of my knowledge, the use of peat based potting mixes probably
> started with or was first seriously studied by, the John Innes Research Institute in
> England.

The John Innes mixes are all soil-based. They include some peatmoss, but the principal 
ingredient is soil. And not just any old soil, at that. It's supposed to be made from 
rotted turves, carefully seasoned with measured amounts of lime.

But perhaps the most important part of the research that led to the JI mixes was a 
careful study of soil sterilization. The conclusion was reached that you should add a 
modicum of superphosphate *after* steam sterilization.

There's a little book on the JI mixes, probably readily available via Alibris or 
ABEBooks. Recommended for anyone who wants to get the info from the horse's mouth.

The JI formulas are useful as a starting point, esp. where adjustment of pH levels is 
concerned, but their use of ingredients you simply can't get -- rotted turf, Cornish 
silver sand -- means you must improvise and use other ingredients.

The UC mixes differ in that they are totally soil-free. They were developed for 
conditions in California, and are not necessarily suitable in other areas. Because they 
use no soil, they contain no clay fraction and adsorb nutrients relatively poorly. (In 
normal soils, nutrients are adsorptively bound to clay particles.) As a result, UC 
mixes require frequent liquid feeding, which may not be appropriate in a dark, dank 
winter climate.

Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate

on beautiful Vancouver Island

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