Lay landscape fabric or cardboard first to stop weeds from growing through

Before you spread mulch, put down a weed barrier — either landscape fabric or cardboard — directly on the soil. This layer blocks sunlight from reaching weed seeds already in the ground, so they cannot sprout up through your mulch. Without it, you will spend the next few months pulling weeds that grow right through the mulch itself.

The barrier also slows how fast mulch breaks down and settles into the soil, so your mulch layer stays thicker longer. This matters because thin mulch does not suppress weeds as well, and it breaks down faster in hot sun.

You do not need both fabric and cardboard — pick one based on what you have on hand and how long you want the barrier to last. Cardboard breaks down in one to two years. Landscape fabric lasts three to five years, depending on thickness and sun exposure.

Key Takeaways

  • Landscape fabric or cardboard blocks weeds from sprouting through mulch and should go down before you spread any mulch.
  • Cardboard breaks down in one to two years and works well for annual beds; landscape fabric lasts longer in permanent plantings.
  • Overlap seams by at least 6 inches so weeds cannot push through the gaps between pieces.
  • Wet cardboard or fabric before laying it down so it stays in place and conforms to the ground.
  • Mulch should sit on top of the barrier, not mixed into it — keep the two layers separate.

Cardboard: the cheapest and fastest option

Cardboard is free or nearly free if you save boxes from deliveries or ask a grocery store for flattened boxes. Lay the boxes flat, overlapping the seams by at least 6 inches so weeds cannot find a gap. Wet the cardboard with a hose before you lay mulch on top — dry cardboard will blow away in wind, and wet cardboard conforms to bumps in the ground.

Remove tape, staples, and plastic windows before laying it down. Tape and staples do not break down and will sit in your soil for years. Plastic windows let light through, so weeds can sprout underneath them.

Cardboard works best in beds you plan to refresh every year or two anyway. It breaks down faster than fabric, especially in wet climates, so by year three you may see weeds pushing through again. In a permanent planting bed — one with shrubs or perennials you do not plan to move — landscape fabric is a better long-term choice.

Landscape fabric: the longer-lasting choice

Landscape fabric (also called weed cloth) is a synthetic material sold in rolls at garden centers. It costs $10 to $30 for a roll large enough to cover 100 to 300 square feet, depending on thickness. Thicker fabric (3 to 4 ounces per square yard) blocks weeds better and lasts longer than thin fabric (1 to 2 ounces).

Lay it the same way as cardboard: overlap seams by 6 inches, wet it before mulching, and remove any staples or labels. Landscape fabric does not break down, so you can leave it in place for three to five years. When it finally degrades from sun exposure, you can pull it out and replace it, or just leave the pieces in the soil — they will not harm plants.

One drawback: landscape fabric can trap water if you do not choose the right type. Buy permeable fabric that lets water drain through. Avoid plastic sheeting or non-woven plastic — those suffocate plant roots and trap moisture.

How to lay the barrier without gaps or wrinkles

Start by clearing the bed of large rocks, sticks, and debris. You do not need to remove every pebble, but anything pointy or bigger than your fist should go. These create bumps that prevent the barrier from lying flat, and gaps let weeds push through.

Unroll your cardboard or fabric across the bed. If the bed is wider than your roll, overlap pieces by at least 6 inches — measure this distance; do not guess. Weeds are good at finding gaps that look smaller than they are. Wet the barrier with a hose so it stays in place and settles into the soil contours.

If you are using cardboard in a bed with existing plants, cut an X-shaped slit over each plant and fold the flaps back. Do not wrap cardboard around the stem — leave 2 to 3 inches of space so air can circulate and the stem does not rot. For landscape fabric, cut a circle around each plant instead of an X; circles are easier to seal back down.

Mulch depth and placement over the barrier

Spread mulch 2 to 4 inches deep over the barrier. This is thick enough to block light and suppress weeds, but not so thick that it smothers plant roots or traps moisture against stems. Measure with a ruler the first time — most people spread mulch too thin because it looks deeper than it actually is.

Keep mulch 3 to 4 inches away from tree trunks and plant stems. Mulch piled against wood or bark holds moisture and invites rot and pest damage. This gap is one of the most common mistakes home gardeners make, so check your beds a few days after mulching and pull mulch back if it is touching any stems.

Do not mix the barrier into the mulch or bury it. The barrier should sit on top of the soil, and mulch should sit on top of the barrier. This separation keeps the barrier doing its job — blocking weeds — and keeps mulch from breaking down into the barrier instead of into the soil.

When you do not need a barrier

A weed barrier is most useful in ornamental beds, vegetable beds, and areas where you do not plan to dig or amend the soil often. If you have a bed where you regularly add compost, turn the soil, or plant new things, a barrier becomes annoying because you have to cut it and patch it every time.

You also do not need a barrier if the soil is already clean — no visible weeds, no recent disturbance, and no history of persistent weeds like bindweed or quackgrass. In that case, 3 to 4 inches of mulch alone may be enough. But if you have ever had weeds in that spot, or if you are starting a new bed in lawn or rough ground, the barrier is worth the 20 minutes it takes to lay down.

Frequently Asked Questions

Can I use newspaper instead of cardboard or landscape fabric?

Yes, newspaper works the same way as cardboard and breaks down at about the same speed. Lay it 4 to 6 sheets thick, overlap the edges by 6 inches, and wet it before mulching. Newspaper is thinner than cardboard, so it tears more easily during installation, but it costs nothing if you have old papers at home.

Will landscape fabric prevent water from reaching plant roots?

Permeable landscape fabric lets water through just fine. Non-permeable plastic sheeting will trap water and should not be used. When you buy fabric, check the label or product description — it should say "permeable" or "breathable" and list a water permeability rate.

How do I remove a barrier after it has broken down?

Cardboard and newspaper break down into the soil and do not need to be removed — they become part of the organic matter. Landscape fabric should be pulled out once it starts tearing or degrading. If pieces are stuck to roots, leave them; they will not harm the plant.

Can I put mulch directly on grass without a barrier?

You can, but the grass will grow up through the mulch for months. It is faster to remove the grass first or lay a barrier on top of it. If you use a barrier, the grass underneath will die from lack of light, and the dead grass becomes organic matter that feeds the soil.

What if weeds are already growing in my mulch?

Pull them out and lay a barrier on top of the existing mulch. You do not have to remove the old mulch first — the barrier will block new weeds from sprouting, and the old mulch will continue to break down underneath.