I have done this, but didn't know to wet it before putting down the mulch. The paper blew all over and I had a terrible time keeping all the soild covered while I put down the mulch. Video: Easy Organic Weed Control with Paper and Mulch – An.
You have to use it when it's not expected to rain for 36 hrs or so. Spray in the morning after the dew has evaporated. 1 qt white vinegar and c epsom salts, dish soap, mixed in water, in a sprayer bottle
Weed killer: 1 gallon vinegar, 2 cups epsom salt, cup dish soap not sure how this is organic unless she uses organic vinegar, organic Epsom salt & organic dishsoap- which I don't think is possible but more or less chemical free.