Do Cedar Chips Prevent Weeds?

Suppression

• All plants require sunlight for photosynthesis -- even weeds. Without it, they are unable to produce the food supply they need to exist. When you spread a layer of cedar chip mulch over the soil, it covers existing and emerging weeds with an umbrella of darkness. With no light peeking through, the weeds are subject to certain death. Even if some weed seeds do manage to germinate under these conditions, the resulting sprouts do not stand a chance without the sun’s rays.

Amount

• How thickly you spread the cedar chips dictates whether or not you are providing a successful weed barrier. For instance, a layer of cedar chips spread 1 to 3 inches thick for ornamental purposes does little to prevent weed penetration. A layer of cedar chips that measures 4 to 6 inches around an ornamental flower bed provides enough suppression to prevent weeds from rearing their heads. If you have areas where weeds are a constant annoyance, spread the cedar chips 8 to 12 inches deep.

Additional Advantages

• Aside from suffocating weeds, cedar chips decompose at a slow rate, feeding the soil as they do so. They also stay put when the weather is windy, so there is no need to worry about them blowing away. Cedar chips help retain moisture levels in the soil, yet are highly resistant to rotting and not subject to mold growth under these damp conditions. Cedar contains a natural insect repellent that can help reduce the insect population within the cedar’s location.

Warning

• When spreading cedar chip mulch over a planting bed or other weed-prone area, avoid pushing the cedar chips up against trees or the main stems of shrubbery. Tapering the cedar chips and forming a doughnut-shaped depression around the trunks and stems of these plants creates a slight gap that allows oxygen to flow freely. Good oxygen flow between the mulch and plant tissue eliminates the dark, moist environment that promotes fungal growth.