spakker wrote:

This reminds me of the 'french' system-a highly intensive growing method-
where all the soil is prepared to a depth of upto 2 feet. As you say many
roots go downwards and I guess that the extra depth of cultivated and
composted soil gives any plants a good advantage

Also known as the Chinese system or Deep Bed system. It seems to have
developed in parallel in places where land prices were very high, and so
getting the biggest yield possible was important to success. The French
system you spoke of was developed by market gardeners working small plots
of land on the outskirts of Paris.

Apologies if you knew all this already!

--
"I know not with what weapons World War III will be fought, but World
War IV will be fought with sticks and stones."
-- Albert Einstein