A simple and affordable weed barrier and soil builder: Cardboard waste is an abundant resource that will probably be around for a long time. By laying cardboard and heavy mulch over areas to be planted, most weeds and grasses are easily choked out. Grasses are generally heavy feeders, which means the grasses themselves contain high levels of nutrients. You end up storing fertilizer in the soil and saving labor, being biodegradable and increasing earthworm activity. Cardboard is important.