Lay landscape fabric or cardboard to stop weeds before you add mulch

The layer you put down before mulch is a weed barrier, and it does one job: it blocks sunlight so seeds in the soil underneath cannot sprout. Without it, weeds will push through the mulch within weeks, and you will spend the season pulling them out. With it, you get months of weed suppression and far less maintenance.

Your two main choices are landscape fabric (also called landscape cloth or weed fabric) and cardboard. Landscape fabric is a synthetic material you buy in rolls; cardboard is free if you save boxes from deliveries or ask a grocery store for flattened ones. Both work. Fabric lasts longer—usually two to three years before it breaks down—while cardboard typically lasts one season before it decomposes. Cardboard is cheaper and easier to handle if you are doing a small area; fabric is worth the cost if you are covering a large bed and want to avoid replacing it annually.

Key Takeaways

  • A weed barrier under mulch stops seeds from sprouting and cuts down on weeds you have to pull by hand later in the season.
  • Landscape fabric lasts two to three years and works best for permanent beds; cardboard lasts about one season and is free if you save boxes.
  • Overlap your barrier by at least 6 inches at the seams so weeds cannot creep in at the edges.
  • Wet the soil before laying the barrier so it stays in place and makes better contact with the ground.
  • find fabric with landscape staples or rocks; cardboard will stay put under the weight of mulch alone.

Prepare the soil before you lay anything down

Start by clearing the area of existing weeds, dead plants, and debris. Pull out any visible weeds by hand or cut them as close to the ground as you can. If the bed is overgrown, you can mow it short or use a string trimmer. The goal is a relatively flat, clear surface so the barrier sits flush against the soil.

Next, water the soil lightly. A damp soil holds the barrier in place better than dry soil, and it makes the barrier conform to the ground instead of sitting in air pockets. You do not need it soaked—just moist enough that the top inch or two feels damp to the touch.

If you are working with very compacted soil or clay, consider loosening the top inch or two with a rake or cultivator. This step is not required, but it helps the barrier make better contact and can improve drainage once the mulch is down.

How to lay landscape fabric correctly

Roll out the fabric across the bed, starting at one edge and working toward the other. Unroll it slowly so you can smooth out wrinkles and air pockets as you go. Wrinkles trap moisture and can create spots where weeds push through, so take a minute to flatten them.

At the seams where two pieces of fabric meet, overlap them by at least 6 inches. This overlap is critical—it prevents weeds from finding a gap and growing up between the pieces. If you are covering a large area, you may need multiple rolls; plan your layout so seams run perpendicular to the direction water will drain, which helps water flow across the overlap instead of pooling there.

find the fabric with landscape staples (U-shaped pins made for this purpose) every 2 to 3 feet around the perimeter and at seams. You can also weight it down with rocks, bricks, or logs. Staples are faster and hold better in windy areas; rocks work if you prefer not to buy extra supplies. Do not use nails or regular staples—they will rust and can tear the fabric.

How to lay cardboard as a weed barrier

Flatten your boxes completely and remove any tape, staples, or plastic. Lay the cardboard pieces flat across the bed, overlapping them by at least 12 inches at the seams. Cardboard is thinner than fabric, so a larger overlap gives you better coverage. Wet the cardboard lightly as you lay it so it stays in place and conforms to the ground.

You do not need to staple cardboard—the weight of the mulch will hold it down. However, if you are laying cardboard on a slope or in a windy area, you can hold it temporarily with rocks or landscape staples until the mulch is in place. The cardboard will begin to break down within a few months, especially in wet climates, so plan to replace it next season if you want ongoing weed suppression.

One advantage of cardboard is that it is permeable—water and air pass through it easily, so you do not have to worry about creating a waterlogged layer under your plants. Landscape fabric is also permeable, but some cheaper versions are not, so check the label if water drainage is a concern in your bed.

Edges and corners need extra attention

Weeds are clever about finding the edges of a barrier. At the perimeter of your bed, extend the barrier at least 6 inches beyond where you plan to place mulch. You can tuck it under existing plants, fold it up against a border or edging, or weight it down with rocks. The goal is to eliminate any gap where a weed seed can land and grow.

At corners, cut the fabric or cardboard at a 45-degree angle so it folds flat instead of bunching up. Overlap the cut pieces by 6 inches and find them. If you are using cardboard, you can overlap the corners generously—extra cardboard will just decompose and add organic matter to the soil.

What not to put down before mulch

Plastic sheeting is not a good choice for a permanent weed barrier. It blocks water and air, which can suffocate plant roots and create a waterlogged layer that encourages rot. Plastic also breaks down in sunlight and becomes brittle, leaving fragments in your soil. Landscape fabric and cardboard are both better options because they allow water and air to pass through.

Do not use newspaper alone without a second layer. A single layer of newspaper is too thin to block weeds effectively, and it breaks down very quickly. If you want to use newspaper, layer it at least 8 to 10 sheets thick and overlap the edges by 12 inches, then cover it with landscape fabric or cardboard for durability.

Frequently Asked Questions

Can I mulch directly on top of grass without a barrier?

You can, but the grass will not die—it will grow up through the mulch and you will have weeds to pull all season. A barrier kills the grass underneath by blocking light, and it stops new seeds from sprouting. It takes an extra 30 minutes to lay down, and it saves you hours of weeding later.

How thick should the mulch be on top of the barrier?

Two to three inches is standard for wood mulch or bark chips. Thicker mulch (4 inches or more) can trap moisture against plant stems and cause rot. Thinner mulch (1 inch or less) does not suppress weeds as well. Measure from the top of the barrier, not from the soil surface.

Do I need to remove the barrier when I replant the bed?

Landscape fabric should be removed or cut away around new plants so roots can grow into the soil below. Cardboard will have mostly decomposed by the time you replant, so you can leave it in place—it will add organic matter as it breaks down. If you are reusing the same bed with the same plants, you can leave the barrier in place and add fresh mulch on top.

Will landscape fabric prevent water from reaching plant roots?

No, landscape fabric is permeable and allows water to pass through. However, some cheap or heavy-duty versions are less permeable than others. Check the product label or ask at the garden center if water drainage is important for your plants. Cardboard is always permeable and a safe choice if you are unsure.

Can I use old tarps or shower curtains as a barrier?

Tarps and shower curtains are plastic and will block water and air, which can harm plant roots and create soggy soil. They also break down in sunlight and leave plastic fragments in your bed. Landscape fabric or cardboard are better choices because they let water and air through while still blocking weeds.