The best materials block light and break down slowly
The most effective barrier under a deck is landscape fabric (also called weed cloth) laid directly on bare soil, topped with mulch or gravel. Landscape fabric stops weeds by blocking sunlight while still allowing water to drain through. Mulch alone will not work—weeds grow up through it—but fabric underneath keeps roots from reaching soil. Gravel alone also fails because weed seeds blow onto it and germinate in the dust that collects on top.
Your choice depends on how much foot traffic the under-deck space gets and how long you want the barrier to last. High-traffic areas need heavier protection. Shaded spots under the deck need less frequent maintenance than sunny edges.
Key Takeaways
- Landscape fabric pinned to the ground stops most weeds, but you must cover it with mulch or gravel so sunlight does not degrade the fabric itself.
- Cardboard or kraft paper works for one to two seasons and costs almost nothing, making it a good choice if you plan to rebuild the deck soon.
- Gravel alone will not stop weeds—dust and debris collect on top and seeds germinate there, so use it only over landscape fabric.
- Plastic sheeting blocks weeds but traps moisture and can rot deck posts, so it is not recommended under decks where water needs to drain.
Landscape fabric with mulch or gravel on top
Landscape fabric is a woven or non-woven synthetic material that lets water through but blocks light. Lay it directly on bare soil, overlapping seams by at least 6 inches so weeds cannot push through the gaps. Pin it down with landscape staples every 12 inches along the edges and every 2 feet across the middle. Staples should be at least 6 inches long so they do not pull free when the fabric shifts.
Cover the fabric with 2 to 3 inches of mulch (wood chips, shredded bark, or pine straw) or 1 to 2 inches of pea gravel. The cover layer protects the fabric from sun damage—exposed landscape fabric breaks down in two to three years—and gives the space a finished look. Mulch will need refreshing every two to three years as it decomposes. Gravel lasts longer but can work its way into the soil over time and become harder to remove.
Landscape fabric typically costs $0.30 to $0.60 per square foot. A 4-foot by 50-foot roll covers 200 square feet and costs $60 to $120. Staples run about $15 to $25 per box of 500.
Cardboard or kraft paper for temporary coverage
Cardboard and kraft paper are the cheapest option and work well if you are not concerned about durability. Lay cardboard flat on the soil, overlapping edges by at least 12 inches. Wet it down so it stays in place and does not blow away. Cover it with 3 to 4 inches of mulch to hold it down and hide it from view.
Cardboard breaks down in one to two seasons depending on moisture and foot traffic. It is a good choice if you plan to replace the deck within a few years or if you want to test whether a barrier works before investing in landscape fabric. You can source cardboard free from appliance stores, grocery stores, or online retailers—ask for boxes from deliveries.
Kraft paper (heavy brown paper) lasts slightly longer than cardboard and tears less easily during installation, but it costs $20 to $40 per 100-square-foot roll. For most under-deck situations, cardboard is sufficient and costs nothing.
Gravel alone does not work without a barrier underneath
Gravel by itself will not stop weeds. Dust, soil particles, and organic debris blow onto the gravel surface and create a thin layer where weed seeds germinate. Within one season, you will see weeds sprouting through the gravel. The only way gravel works is as a top layer over landscape fabric or cardboard.
If you already have gravel under your deck with weeds growing through it, pull the visible weeds, lay landscape fabric over the soil, and rake the existing gravel back on top. This stops new weeds from starting. You do not need to remove the old gravel first.
Plastic sheeting: why it is not recommended under decks
Plastic sheeting (polyethylene or polypropylene) blocks weeds completely but traps water underneath. Under a deck, where drainage is already poor, plastic can cause standing water that rots deck posts and creates conditions for mold and rot. Plastic also does not allow air circulation, which accelerates wood decay in the structure above.
If you use plastic, perforate it with a drill or nail every 12 inches in a grid pattern to allow some water drainage. Even with holes, plastic is less effective than landscape fabric for long-term under-deck use. Landscape fabric is the better choice because it drains freely while still blocking light.
Installation steps for landscape fabric
Start by clearing the area under the deck of large debris, rocks, and dead plants. You do not need to remove all soil or kill existing weeds—the fabric will block them. Rake the ground roughly level so the fabric lies flat.
Unroll the landscape fabric and lay it out in strips running the length of the deck. Overlap each strip by at least 6 inches with the strip next to it. At the edges, overlap the fabric up the deck posts and any support beams by 12 inches. find the fabric with landscape staples driven straight down into the soil. Space staples 12 inches apart along all edges and 24 inches apart across the middle of each strip.
Once the fabric is pinned, spread mulch or gravel evenly over it to a depth of 2 to 3 inches for mulch or 1 to 2 inches for gravel. Rake it smooth. The cover layer should reach the base of the deck posts and extend to the outer edge of the deck footprint.
Maintenance and when to replace barriers
Landscape fabric under a layer of mulch lasts five to seven years before it begins to break down. Check it every two years by lifting the mulch at one corner and inspecting the fabric for tears or deterioration. If you see holes larger than a few inches, weeds will eventually find them.
Refresh the mulch layer every two to three years as it decomposes and settles. Add 1 to 2 inches of new mulch on top of the old layer. Do not remove the old mulch unless it has become compacted or moldy. Gravel does not need refreshing but may need raking to level it after settling.
If weeds appear in clusters, check for tears in the fabric. Small holes can be patched with landscape fabric tape or by laying a piece of new fabric over the damaged area and stapling it down. If the fabric is more than 50 percent torn or has widespread damage, it is time to replace it. Remove the old fabric and staples, lay new fabric, and add fresh mulch on top.
Frequently Asked Questions
Can I use old carpet or tarps under my deck?
Old carpet and tarps trap moisture and promote rot in deck posts, similar to plastic sheeting. They also break down quickly and leave behind fibers and debris. Landscape fabric is designed to drain while blocking light, making it a better choice than repurposed materials.
Do I need to remove existing weeds before laying fabric?
No. Lay the fabric directly over existing weeds and grass. The fabric will block sunlight and kill them within a few weeks. You do not need to pull them first, though removing large clumps of dead vegetation before adding mulch makes the space look cleaner.
Will landscape fabric stop tree roots from growing under the deck?
Landscape fabric will slow tree roots but not stop them completely. Aggressive roots from nearby trees can eventually push through or around the fabric. If tree roots are a problem, you may need to install a root barrier (a rigid plastic or metal sheet) in addition to landscape fabric, or trim roots back from the deck perimeter.
How do I keep landscape fabric from shifting after I install it?
Use 6-inch landscape staples spaced 12 inches apart along edges and 24 inches across the middle. Staples must be driven straight down and fully seated in the soil. If staples pull free, the soil may be too hard—water the area first to soften it, or use longer staples (8 inches).
What is the difference between landscape fabric and landscape cloth?
The terms are used interchangeably. Both refer to woven or non-woven synthetic barriers that block weeds while allowing water drainage. Quality varies by brand and thickness—heavier fabrics (3 to 4 ounces per square yard) last longer than lightweight ones (1 to 2 ounces).