Landscape fabric and cardboard are the two most effective barriers to put under mulch

Landscape fabric is the standard choice. It blocks weeds while letting water and air reach the soil below. Most landscape fabrics are woven polypropylene — they last three to five years before breaking down, and they cost between $0.10 and $0.30 per square foot. You lay it flat over bare soil, overlap the seams by at least six inches, and cover the edges with mulch so it stays in place.

Cardboard is cheaper and biodegradable. Flatten boxes, remove tape and staples, and lay them overlapping on bare soil. Cardboard breaks down in one to two years, so you are replacing it more often, but it costs almost nothing if you save boxes from deliveries. It also improves soil as it decays, adding organic matter that landscape fabric does not.

Both methods work best when you put at least three inches of mulch on top. The mulch holds the barrier down, hides it, and adds its own weed suppression. Without mulch, landscape fabric shows and cardboard dries out and tears.

Key Takeaways

  • Landscape fabric blocks weeds for three to five years and costs $0.10 to $0.30 per square foot, making it the longest-lasting option for permanent beds.
  • Cardboard is free or nearly free if you save boxes, breaks down in one to two years, and improves soil as it decays.
  • Overlap seams by at least six inches on either barrier so weeds cannot push through the gaps.
  • Three inches of mulch on top holds the barrier down and adds extra weed suppression that the barrier alone cannot provide.
  • Newspaper is a third option that costs nothing but tears easily and breaks down within a year, so it works best in small areas or temporary beds.

How landscape fabric stops weeds

Landscape fabric works by blocking light and creating a physical barrier that weed seeds cannot push through. The woven type (not plastic sheeting) allows water to drain through and roots to reach nutrients below, so plants you want to keep do not suffer. The fabric itself does not rot or compress like cardboard does.

The trade-off is cost and permanence. Once you lay landscape fabric, you are committed to it for years. Removing it later is tedious — it gets tangled with roots and breaks into pieces. If you want to change the bed layout or add new plants, you have to cut holes and patch, which defeats the purpose of having a continuous barrier.

When cardboard is the better choice

Cardboard works well if you are treating a one-time weed problem, building a new bed, or working with a tight budget. It suppresses weeds just as well as fabric for the first year, and it does not create a permanent installation you have to remove later.

Cardboard also feeds the soil. As it breaks down, it adds carbon that microbes use to build soil structure. After two years, the cardboard is gone but the soil underneath is often richer than it was before. Landscape fabric adds nothing — it just sits there until you pull it out.

The downside is replacement. You will need fresh cardboard every year or two, especially in wet climates where it breaks down faster. In dry climates, cardboard can last longer, but it still requires monitoring and patching where it tears.

Newspaper as a free alternative

Newspaper is free if you have it on hand, and it blocks weeds the same way cardboard does. Use at least five to eight sheets thick — single layers tear too easily. Overlap the sheets by at least a foot so weeds cannot find gaps.

Newspaper breaks down faster than cardboard, usually within six months to a year. It also tears more easily when you walk on it or when mulch shifts. Use newspaper in small beds, around trees, or in areas where you do not need the barrier to last more than one season.

How to install a barrier correctly

The most common mistake is leaving gaps. Weeds will find any seam that is not overlapped. Lay your barrier material flat on bare soil, then overlap every seam by at least six inches. If you are using landscape fabric, stake it down with landscape pins every few feet so wind does not shift it before you add mulch.

For cardboard and newspaper, weight them down with rocks or boards while you work. Once you spread mulch on top, the weight of the mulch holds everything in place. Do not skimp on mulch depth — three inches is the minimum. Two inches leaves gaps where light reaches the soil and weed seeds still germinate.

Cut holes only where you need them. Each hole is a place where weeds can creep in around the edges. If you are planting shrubs or perennials, cut the smallest hole that fits the root ball, then pull the barrier material up around the stem so it sits snug against the plant.

Comparing cost and lifespan

Landscape fabric costs more upfront but lasts longer, so the per-year cost is lower if you keep the bed for five years or more. A 100-square-foot bed with mid-range fabric costs about $15 to $20 installed. Cardboard costs almost nothing if you save boxes, or $5 to $10 if you buy it. You will replace cardboard every one to two years, so the long-term cost depends on how long you keep the bed.

For a permanent bed around a house or under established trees, landscape fabric usually makes sense. For a vegetable garden, annual flower bed, or temporary project, cardboard or newspaper is often the smarter choice because you can change the layout without fighting with old fabric.

What not to put under mulch

Plastic sheeting blocks weeds but also blocks water and air. Roots cannot breathe, water pools on top, and the soil underneath stays cold and wet. Plastic is a poor choice for any bed where you want plants to thrive. It works only for temporary situations where you want nothing to grow at all.

Do not use treated wood chips or dyed mulch directly on bare soil — use a barrier first. The barrier keeps the mulch from mixing into the soil, which extends the life of the mulch and keeps the bed looking neat. Landscape fabric or cardboard both serve this purpose.

Frequently Asked Questions

Can I use landscape fabric without mulch on top?

You can, but it will not last as long. Sunlight breaks down the fabric faster, and without mulch weight it shifts and tears. Mulch also hides the fabric so the bed looks finished. Three inches of mulch on top extends the life of the fabric and improves weed suppression.

Will cardboard attract slugs or pests?

Cardboard can provide shelter for slugs and other insects, but so does mulch. The barrier itself is not the problem — it is the moist environment under the mulch. If slugs are an issue in your garden, they will be present whether you use cardboard, fabric, or nothing. Manage them with the same methods you would use anyway.

How do I remove landscape fabric later?

Pull it up in sections, working slowly so it does not tear into pieces you cannot find. Roots will have grown through it, so cut those as you go. Rake the area after removal to pick up fragments. It is tedious work, which is why cardboard is better if you think you might want to change the bed in a few years.

Does the barrier stop all weeds?

A barrier stops weeds from germinating in the soil below, but windblown seeds can still land on top of the mulch and sprout there. Pull those weeds by hand when they appear — they come out easily because they have no roots in soil. A good barrier stops 90 percent of the problem; the remaining 10 percent is hand-pulling.

Can I layer cardboard and landscape fabric together?

Yes, and some gardeners do this to get the benefits of both — the cardboard feeds the soil while the fabric extends the lifespan. It costs more and is harder to remove later, but it works. Use one layer of each, not multiple layers, or water will not drain through.