Mulch Weed Control – Tips On Getting Rid Of Weed Growth In Mulch

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By Mary H. Dyer, Master Naturalist and Master Gardener

Weed control is one of the primary reasons for applying mulch, yet pesky weeds may persist, even through a carefully applied layer of bark chips or pine needles. This happens when weed seeds are buried in the soil or are distributed by birds or wind. What should you do if you’ve got weeds coming up in mulch in spite of your best intentions? Keep reading for a few helpful tips.

Getting Rid of Weed Growth in Mulch

Manual Mulch Weed Control

Mulch acts as physical barrier against weeds, but it must block sunlight in order to be effective. If you notice weeds coming up in mulch, you may need to thicken the layer as blocking light generally requires at least 2 to 3 inches (5-7.6 cm.). Replenish mulch as it decomposes or blows away.

How to Kill Weeds in Mulch with Herbicides

Other than hand-pulling, mulch is probably the single most important means of weed control. However, mulch works best when used as part of a multi-pronged approach along with pre-emergent herbicides.

When used correctly before weeds sprout in early spring, pre-emergent herbicides are one effective way to prevent weeds coming up in mulch. They won’t, however, do anything for weeds that have already sprouted.

To stop weeds in mulch with pre-emergent herbicides, begin by raking mulch off to the side, then hoe or pull any existing weeds. Apply the product, following manufacturer directions to the letter. Pay attention to the label, as some plants don’t tolerate certain types of pre-emergent herbicides.

Replace the mulch carefully, being careful not to disturb the just treated soil. At this point, you can provide extra protection by applying another layer of herbicide over the mulch. A liquid herbicide works best because it adheres to the mulch instead of falling through to the soil.

A Note about Glyphosate: You can use glyphosate to stop weeds in mulch, but this approach requires extreme care because glyphosate, a broad-spectrum herbicide, will kill any broad-leaved plant it touches, including your favorite perennials or shrubs. Apply glyphosate directly to weeds, using a paintbrush. Be extremely careful not to touch nearby plants. You can also protect plants by covering them with a cardboard box while you’re applying the herbicide. Don’t remove the box until the treated weeds have time to dry completely.

Preventing Weeds with Landscape Fabric

If you haven’t applied mulch yet, landscape fabric or weed barrier cloth is a safe way to block weeds while still allowing water to pass through to the soil. Unfortunately, landscape fabric isn’t a perfect solution because some determined weeds will push through the fabric, and those weeds will be extremely difficult to pull.

Sometimes, good old hand-pulling is still the most effective way of getting rid of weed growth in mulch.

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