How to Smother Weeds

Smothering weeds is a simple, natural way to get rid of these unwanted plants without using potentially harmful herbicides or breaking your back pulling them by hand. Smothering weeds works because the plants don't get any water or light, which they need to germinate and grow. As a bonus, the smothered weeds and the organic mulching material both add nutrients and organic matter to the soil when they decompose.

Organic mulches smother weeds and also regulate soil temperature and keep the soil moist. In addition, organic materials often host crickets and carabid beetles that eat weed seeds.

Several mulching materials make good to excellent weed-smothering materials:

Chopped leaves

Grass clippings

Seaweed

Peanut, rice and buckwheat shells 

Straw

Pine needles

Shredded or ground bark

Wood or bark chips

Apply materials in layers 2 to 3 inches deep, but don't allow the mulch to touch plant stems and tree trunks or you risk smothering desirable plants or encouraging plant diseases. Replenish these mulching materials as needed to keep layers between 2 and 3 inches deep.

Smothering with mulch works best on young weeds. 

Place organic mulches around cool-season vegetable plants as the need arises. If you plan to mulch around warm-season crops, wait until the soil temperature reaches at least 60 degrees Fahrenheit. 

Don't make mulch layers thicker than 3 inches or you risk depriving the soil of oxygen.

Although hay is excellent for smothering weeds, it frequently contains weed seeds that can cause future problems.

Placing a layer of newspaper beneath organic mulch kills weeds faster than using the mulching material alone.

Mow, hoe or cut off the tops of weeds until the unwanted plants stand no taller than 1 inch. Deeply water the soil in the treatment area.

Don't till weeds or you risk spreading their seeds or rhizomes.

Lay down layers of newspaper 10 to 12 pages thick. Overlap the newspapers by about 2 inches so weeds can't poke up through cracks. Prevent the newspapers from blowing away by giving them a short blast of water from a garden hose.

You can use flattened pieces of cardboard in place of the newspaper. 

Use only newspaper sheets with black-and-white print. Colored pages might contain lead.

Don't use paper or cardboard if it has a waxy coating.

Apply a layer of organic mulching material evenly over the newspapers. Harvest to Table suggests using an 8-inch layer of straw or 2 inches of grass clippings, but make sure your chosen material is weed-free. The Manhattan Beach Botanical Garden recommends applying a 5- to 7-inch layer of wood chips, bark or dried leaves, while Mother Earth News suggests placing a 2- to 3-inch layer of pine needles on top of the newspaper layers.

To keep existing plants healthy, leave about 3 inches of mulch-free space around small plants, 4 inches around shrubs and at least 6 inches around tree trunks.

Wet down the mulching material with water from a garden hose until it has compacted. Dampening the mulch material gives helps it decompose faster.

Allow the smothering mulch to sit for at least one growing season. Leave it in place for a year if you're trying to smother tough perennial weeds with long taproots. Replenish the mulch, as necessary, to maintain its original thickness.

If you spot weeds poking through the mulch, pull them out by hand.

Laying landscaping fabrics over weeds smothers the pesky plants while still allowing water, air and nutrients to get down to the soil. Sunset suggests using landscaping fabric in areas where you don't change plants often, such as around shrubs and trees. It's typically too labor-intensive to use the products around annual flowering plants and vegetable crops.

Lay the landscape fabric over the bed, making sure the edges overlap by at least 3 inches so weeds have no place to sprout. Cut an X in the fabric so it will go over existing plants. Anchor down the edges with landscape staples or pegs. Covering landscaping fabric with a 2- to 3-inch layer of organic mulching material makes it look more attractive and prevents the fabric from degrading in the sun.