If you have even seen or used the organic Preen you can have your own made for a whole lot less if you have a feed mill close that grinds cattle feed and stock corn gluten pellets. If you read the front label in the lower lefthand corner where it lists the ingredients, it states 100% corn gluten.
Last time I bought the pellets they were around $210.00 per ton. I had them run 500 lbs. through their hammer mill into meal for around $50 + 5 for a grinding fee. Took my own feed bags because they used to charge $1.00
ea.
Applied it per the Preen instructions, like 1 oz. per sq. ft. after all plants had established roots, then stirred it in the top 1-1/2" or so. It's best to do it ahead of a nice rain.
What it does is allows weed seed to germinate but stops them from growing roots so they can't absorb water or nutrients and die. It will keep 99% of any weeds from growing, I only had 2 kinds come up but were sparse. Purslane is one that is not affected by it, can't really remember the other one but may have been Jimson Weed.
You'll probably get a funky little mold on the surface of the soil, but it will keep weeds at bay for 6-8 weeks. I would advise using what you had ground as I had extra and thought I'd give it a second treatment later. I stored it in trash cans with a lid to keep the mice out, but it molded somewhere along the line.
I don't use it anymore since using the leaves for mulch, but it did work great when I did use it. You just don't want to disturb the surface much, just how out any weed that may come up, or just pull them.