Most importantly, it offers some of the best prices in the industry. If that was not enough, there are weeds that humans are guilty of spreading. Also, use a layer of organic mulch wood chips or landscape fabric to prevent seeds from germinating or having the light they need to grow.  Source: <a href=http://en-plasturgie.cmic-sa.com/7-cfr-В§-201-sixteen-noxious-weed-seeds-digital-code-of-federal-regulations-e-cfr-lii-legal-data-institute>http://en-plasturgie.cmic-sa.com/7-cfr-В§-201-sixteen-noxious-weed-seeds-digital-code-of-federal-regulations-e-cfr-lii-legal-data-institute</a>