Answer: Screened composition mulch material is fine for mulching. As long as it is thick enough, weeds should not grow where you've placed your mulch. Casoron is a pre-emergent herbicide. It stops weed seeds from germinating by emitting a gas. It isn't harmful to you, just to the weeds. Bark chips or bark nuggets aren't any better or any worse than your screened comp. The only difference is in the size of the pieces. Bark nuggets or chips are larger and therefore will take longer to decompose. In other words, you won't have to replace the bark as often as you will the screened material. But, either one will work well as a mulch material.
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