By modifying the conditions that weeds need grow, you can sometimes make it difficult or impossible for them to survive. Mulching in early spring is one way of doing this. It can prevent light from reaching germinating weeds in garden walkways, areas around perennial plants and along fencelines.
Organic mulches, such as straw, sawdust, or wood chips can be inexpensive or even free, and will eventually add organic matter to the soil. Organic mulches tie up nitrogen as they are decomposing, which helps to suppress some (but not all) weed growth; be aware it can also suppress growth of desirable plants until the mulch is decomposed. Light organic mulches, such as straw, should be applied about six inches deep. But heavier mulches, such as wood chips, sawdust or leaf mold should be limited to a depth of about four inches or less because they can pack densely, restricting water and air penetration into the soil. Keep mulches several inches away from stems of desirable plants to prevent diseases caused by moisture retention. Strong perennials, such as Canada thistle, field bindweed, and quackgrass can penetrate most organic mulches. When obtaining organic mulches, be sure they do not contain weed seeds or herbicide residues that can damage desirable plants. Many organic mulches are blown by winds; winter mulches over garden areas and flower beds can be kept in place with chicken wire or other durable mesh with openings large enough to allow air circulation.
Gravel or crushed rock mulch can be quite effective and can also be used as an attractive cover over synthetic mulches. It has the disadvantage of migrating into garden beds and lawns unless restrained by edging, and it can be expensive. Use darker colored gravel or rock because light colors can reflect excessive heat onto desirable plants.
Synthetic mulches, such as black plastic, woven weed mats and roofing paper are often used well in combination with other mulching materials. Woven weed mats are expensive if used on large areas, but are worth the cost for long-term weed control. They allow air and water to penetrate soil. Roofing paper is durable and long lasting. It works well under gravel on driveways and along fencelines. Use 80-pound grade for durability. Black plastic is one of the least desirable mulches. It breaks down in one season and shoots of many stronger perennial weeds will break through it. Desirable plants will have weak root systems under plastic mulches and slugs and diseases can be problems. See MSU Extension bulletin #58 for more information on mulching.
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