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How Much Bark Mulch for Weed Suppression?

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Garden bark mulch has many functional uses in the landscape, including helping to suppress weeds, although it doesn’t provide an impenetrable weed barrier. It’s an organic form of mulching, conditioning the soil as it deteriorates. You shouldn’t layer bark mulch too deeply or problems with moisture and disease can put the plants’ health at risk.

Garden Bark Mulch for Landscaping

Bark mulch is used with ornamental shrub planting as a method of weed control. Bark mulch suppresses weeds by blocking light that seeds need to germinate, but it doesn’t completely prevent weeds. It also helps retains moisture in the soil and keeps plant roots cool in hot weather. Bark mulch resists compaction, it doesn’t blow away and it provides an attractive finish to newly planted areas. It’s also a by-product of the lumber industry and so readily available.

Bark mulch typically comes from milled fir, pine, redwood and spruce logs, notes Clemson Cooperative Extension. Landscape bark mulch is graded according to particle size, ranging from bark chunks or nuggets, bark granules and shredded bark. Bark chunks last the longest and granules are useful for soil conditioning. Bagged bark mulch has usually weathered enough to destroy any toxins that may harm plants. The coarse bark mulches are more effective for weed suppression; seeds can germinate in fine, moist bark mulch.

Mulch Depth to Prevent Weeds

Bark mulch applied in excessively thick layers creates a moist environment that inhibits oxygen penetrating into the soil and invites root and stem rot disease. Layers that are too thick also keep water from infiltrating the soil, depriving plants of water and oxygen. Spread coarse bark mulch — chunks or nuggets — to a uniform depth of 3 to 4 inches and fine mulch 2 inches deep, recommends University of Arkansas. Air and water enters the soil more easily through the large pieces of bark than fine bark mulch.

To determine how much mulch you’ll need for an area, use an online mulch calculator. You’ll need to know the width and length of the project area to determine the square footage of the bed you plan to mulch, along with the depth of mulch you want to apply to the area.

Additional Mulching Considerations

Bark chunks or nuggets are suitable for shrub beds and trees; apply finer granules to perennial and annual beds. Pull bark mulch away from the stems of plants, especially in the spring and for disease-prone plants such as roses — soil is slower to warm in the spring with a layer of mulch on it, and moisture trapped around the stem creates favorable conditions for the growth of fungi.

Bark mulch needs to be replenished to the correct depth for the first few years while plants establish. Use a layer of landscape fabric under bark mulch if possible to help suppress weeds. Mulch on top of landscape fabric is not recommended for areas with steep slopes, as the mulch tends to slide down on the landscape fabric. Physical barriers like landscape fabric are recommended around trees, shrubs and perennial beds.

How Much Bark Mulch for Weed Suppression?. Bark mulch has many functional uses in the garden, including helping to suppress weeds, although it doesn’t provide an impenetrable weed barrier. It’s an organic form of mulching, conditioning the soil as it deteriorates. You shouldn’t layer bark mulch too deeply …