Smothering kills weeds by blocking sunlight and air, so they starve instead of being pulled or sprayed

Smothering is a method where you cover weeds with a material thick enough to prevent light from reaching them. The weeds die because they cannot photosynthesize, and the roots eventually break down in the soil. Unlike pulling, smothering works on established weeds and large patches. Unlike chemicals, it leaves no residue and costs very little. The trade-off is that it takes weeks or months, and you cannot use the covered area during that time.

The method works best on weeds that are already growing in a bed or garden you plan to replant anyway. It is less practical if you need the space when ready or if you are trying to kill weeds in a lawn where you want grass to grow back.

Key Takeaways

  • Cardboard and newspaper are the cheapest smothering materials and break down into the soil after the weeds die.
  • You need a layer thick enough to block light completely—single-layer newspaper will not work, but five to ten sheets will.
  • Wet the material after laying it down so it stays in place and speeds decomposition.
  • Smothering takes four to twelve weeks depending on the weed type, season, and material thickness.
  • Overlap your material by at least six inches at the edges so weeds cannot push through the gaps.

Cardboard as a smothering layer

Cardboard is the most common choice because it is free or cheap, breaks down naturally, and blocks light effectively. Use single-wall cardboard boxes (the kind most packages come in), not double-wall. Flatten the boxes and lay them directly over the weeds without removing them first. Overlap each piece by at least six inches so weeds cannot find gaps to grow through.

Wet the cardboard thoroughly after laying it down. This keeps it from blowing away, helps it conform to the ground, and speeds the decomposition that will eventually feed your soil. Cardboard typically breaks down completely in six to twelve months, depending on moisture and temperature. In warm, wet climates it breaks down faster; in cold or dry climates it lasts longer.

Remove any tape, staples, or plastic windows before laying cardboard down. These do not decompose and will remain in your soil. If the cardboard has a plastic or wax coating (common on produce boxes), it will break down much more slowly—use it only if you are willing to wait a year or more.

Newspaper and other paper materials

Newspaper works if you use enough layers. A single sheet will not block light; you need five to ten sheets stacked together. Wet the stack as you build it so the sheets stay bonded. Overlap the stacks by at least six inches, just as you would with cardboard.

Newspaper breaks down faster than cardboard—usually in two to four months—because the paper is thinner and more porous. The ink is soy-based in modern newspapers and poses no hazard to soil or plants. Avoid glossy inserts and colored sections if possible, though they will decompose eventually.

Paper materials work best in beds where you plan to add compost or mulch on top. The weight of the added material holds the paper down and speeds decomposition. Without that weight, paper can shift or curl at the edges, creating gaps where weeds escape.

Landscape fabric and other synthetic materials

Landscape fabric (also called weed cloth) is a woven synthetic material sold in rolls at garden centers. It blocks light and allows water to pass through, so it does not create the waterlogging that cardboard sometimes causes. Landscape fabric lasts three to five years before breaking down, which makes it useful if you want the barrier to remain in place while you replant.

The downside is cost—landscape fabric runs several dollars per square foot, while cardboard is free. It also does not add organic matter to the soil as it breaks down. If you choose fabric, find it with landscape pins or staples every few feet so wind and weeds cannot lift the edges.

Avoid plastic sheeting (the kind used for painting or construction). Plastic blocks water as well as light, which can create soggy, anaerobic soil underneath. It also does not break down, so you will have to remove it by hand after the weeds die.

Layering cardboard with mulch or compost

Adding a layer of mulch or compost on top of cardboard speeds the process and improves the final result. Spread two to four inches of wood chips, shredded leaves, or compost over the cardboard after you have laid it down and wetted it. The weight holds the cardboard in place, the organic material feeds soil organisms that break down the cardboard, and the finished bed is ready to plant when ready after the weeds die.

This approach works especially well in garden beds where you are preparing soil for new plants. By the time you are ready to plant, the cardboard has mostly decomposed and the mulch has settled, creating a rich planting surface. The weeds underneath have been dead for weeks and their roots have begun to break down.

How long smothering takes and what to expect

Smothering typically kills weeds in four to twelve weeks, depending on the weed type, material thickness, temperature, and moisture. Annual weeds (those that live one season) die faster than perennial weeds (those that return year after year). Thick materials like cardboard take longer than thin ones like newspaper, but they are also more reliable.

You will see the first signs of death in two to three weeks—the weeds will yellow and wilt. Do not remove the covering yet. Leave it in place for at least four weeks after the weeds stop growing, so the roots have time to break down and cannot regrow if the covering shifts. In cool weather or with thick materials, wait eight to twelve weeks.

If you see weeds pushing through the edges after four weeks, the overlap was not wide enough or the material has shifted. Add more material to the edges or weight down the covering with rocks or soil.

Preparing the area before you smother

You do not have to remove weeds before smothering them, but you should remove any tall, woody growth. Weeds taller than a few inches will take longer to die because they have more stored energy in their stems and roots. Cut them down to ground level with a weed whacker or pruners, then lay your smothering material directly over the cut stems.

Mow the area if it is overgrown, or pull any large thistles or brambles by hand. The goal is to get everything as close to ground level as possible so the smothering material lies flat. Gaps between the material and the soil allow light to reach the weeds and slow their death.

Water the soil before laying down cardboard or newspaper. Moist soil speeds decomposition and helps the material conform to the ground. Dry soil can cause the material to sit on top without making full contact, creating air pockets where weeds can survive.

Frequently Asked Questions

Can I smother weeds in a lawn where I want grass to grow back?

Not with this method. Smothering blocks light from everything underneath, including grass seed. If you want to kill weeds in a lawn and keep the grass, use spot treatments (pulling, digging, or targeted herbicide) instead. Smothering works best in beds where you are replanting anyway.

Will cardboard kill the soil or make it toxic?

No. Cardboard is made from wood pulp and breaks down into organic matter that feeds soil organisms. As it decomposes, it improves soil structure and water retention. Avoid cardboard with plastic coatings or heavy inks, but standard brown cardboard is safe.

What if I need to use the space before the weeds are completely dead?

You can plant through the cardboard or fabric once the weeds have stopped growing (usually four to six weeks). Cut an X through the material where you want to plant, pull back the flaps, and plant into the soil below. The material will continue to decompose around the new plant.

Do I have to overlap the material by six inches?

Six inches is the minimum for most weeds. Perennial weeds with aggressive roots may need eight to twelve inches of overlap. The wider the overlap, the less likely weeds will find a gap and push through. If budget is tight, six inches works for annual weeds in most situations.

Can I smother weeds in winter?

Yes, but it takes longer. Cold slows decomposition and weed death. Lay the material in fall or early winter, and expect the weeds to be fully dead by late spring. The advantage is that you can prepare beds in winter and have them ready to plant in spring without waiting through the growing season.