On Tue, 02 Dec 2003 13:36:38 -0500, Trent-Lion opined:

In the GH I am restoring, I put some old paving bricks down to cover
the dirt floor before thinking about the potential weed problem. Is it
safe to use Roundup on the weeds that come up inside the GH, or should
I go to the trouble of removing all the bricks and putting down
weed-blocking cloth? Thanks.
T-L

Go through the trouble. Roundup does not prevent weeds from sprouting up. It's
a systemic pesticide which must make contact with the foliage, and in a
greenhouse the drift can vary and cause you to lose plants.