The message
from Janet Baraclough contains these words:

Covering ground with black plastic, or carpet, to clean ground of
serious perennial weeds like GE, requires that all light is excluded.
Holes in the plastic let light in, shoots will emerge through them and
photosynthesise to feed and multiply the roots below. I see no point
mulching on top of a non-degradable or incredibly slow degrading
soil-barrier such as plastic or carpet.

Oh, I can. One of my friends had a plot of almost virgin clay, covered
in rank and weedy weeds. He covered it with throwouts from the
greengrocer for months, then capped it with bales of straw and old
carpet on top of that, all soaked during the construction with the
contents of his netty.

Then he covered the lot with thick plack polythene and left it for two
years. The ground is free of weeds, even the seeds having been cooked in
the initial composting, and the worms turned it all into good deep
friable loam.

So, even a little (compostable) mulch will be beneficial.

I'm doing a simiar trick with my garden, a bit at a time.

--
Rusty Hinge
horrid·squeak&zetnet·co·uk
http://www.users.zetnet.co.uk/hi-fi/tqt.htm