Geaux

why scrape and remove if you have killed the weeds then tilled the area?

Just make sure the weeds are really dead.

quote:

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1. Kill weeds: Check
2. Till the area (river silt and weeds):
3. Scrape & remove 2-3" of the dirt/weeds

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No reason to do #3 if you're doing the first 2. There are likely seeds that won't get killed from herbicides, so you could lay down a layer of landscaping fabric before you add you're 'build-up' layer of soil.

As someone else said, I'd definitely put some sort of edging. Either stones/bricks or metal edging; don't use the flexible plastic garbage.

Agree with the guys above. 2 & 3 are probably redundant (no harm, just probably unnecessary to do both) and you’ll want to make sure you’re not going to have grass creeping back in through the mulch.

quote:

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Are weed barriers necessary between existing tilled dirt, and new built up soil?

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If you mulch the bed really well, say 4 to 5 inches, you won't need fabric in the area you plant. Mulch that thick and deep won't allow weeds to sprout up. I would just apply fabric where the edging is and a few inches into the bed area.