Stirring them occasionally so the surface of the mulch will dry eliminates the mold. Insects and rodents may overwinter in some organic mulch. Poison baits can be used to eliminate rodents, which may damage plants. Weed seeds may be introduced into the garden with hay or straw or strawy manure. If you use various kinds of hulls or corncobs, be sure they are free of the grain or seed.
Grain mixed in with crushed corncobs can attract rodents.
To control weeds, mulch needs to be sufficiently deep, or weeds from the soil below will grow through it. Organic Mulch Materials Grass Clippings Grass clippings are readily available when the lawn is actively growing. Using grass clippings has several disadvantages, however. Weeds from the lawn can be introduced into the mulched bed. If the clippings are applied too deeply and packed too tightly they will release heat and a foul odor as they decay.