Hi John,
I use “damp proof course” plastic sheeting size 1200 which builders use in house construction. This is black and heavy duty.
It is very cheep, certainly way cheaper than Mypex, and very very effective at excluding light.
I cover the ground with well rotted Compost and then cover with the DPC and leave this on for 6 months, usually Autumn and Winter. In Spring I’m left with completely clean ground covered in fine crumbly Compost into which I can immediately start planting.
It’s not exactly Charles’s method but it works well for me.
I should stress this is the approach I use for new ground, for established areas I just add 1 to 2″ of well rotted Compost after harvesting a crop.
Don.