Why do weeds grow on top of landscape fabric?

Because mulch turns into soil. Wood chips, bark and shredded hardwood decompose from the bottom up, and within two or three seasons there is a half-inch to an inch of fine organic matter sitting on the fabric. Windblown weed seeds land in it, germinate, and send roots down through the weave, which is porous by design. At that point the fabric is anchoring the weeds rather than stopping them, and pulling them tears the material. This is the single most common complaint from homeowners who installed fabric under mulch.

Does landscape fabric hurt plants?

It can, over time. Fabric interrupts the natural cycle in which mulch breaks down and organic matter is worked into the soil by earthworms and soil organisms, so soil beneath long-standing fabric often becomes compacted and low in organic matter. Shrub and perennial roots also grow into the weave and are damaged when the fabric is later pulled. Extension horticulturists at several land-grant universities make exactly this point when advising against fabric in ornamental beds.

Does fabric stop mulch from washing away on a slope?

Not reliably, and it can make things worse. Mulch slides on the slick surface of a fabric sheet more readily than it does on bare soil, particularly with smooth bark nuggets on a slope steeper than about 3 to 1. Better answers on slopes are shredded hardwood mulch, which knits together and stays put, plus terracing, edging at the toe of the slope, or an erosion-control blanket made of straw or coir that biodegrades as plants establish.

Is there any planting bed where fabric makes sense?

A few. Beds planted permanently with shrubs that will not be divided or replaced, mulched with stone rather than bark, are a reasonable case, since stone does not decompose into a seed bed. Fabric also helps as a temporary barrier where an aggressive perennial weed is being suppressed, and around utility or equipment pads where nothing is meant to grow. The common factor is that nothing about the bed is expected to change and no organic mulch is involved.

What is the best weed barrier if not fabric?

Cardboard or several sheets of newspaper under 3 inches of mulch, a technique widely used in sheet mulching. It blocks light long enough to kill existing weeds, then decomposes within a season or two and feeds the soil instead of leaving plastic behind. Plain thick mulch alone suppresses most annual weeds. For perennial weeds with deep roots, no barrier substitutes for digging them out first, because they will find any seam or edge.

Should You Put Landscape Fabric Under Mulch?

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated October 2026

Over-the-shoulder view of a person laying a stone paver into a sand base while building a garden path, in soft overcast light

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Generally no. For planting beds mulched with wood chips or bark, most extension horticulturists and professional landscapers advise against landscape fabric. The reason is simple: organic mulch decomposes into a fine layer of compost on top of the fabric, weed seeds germinate in that layer, and their roots grow straight through the porous weave. Within two or three years the fabric is holding weeds rather than blocking them, while also cutting the soil off from the organic matter that mulch is supposed to deliver. Fabric belongs under gravel and stone, not under bark mulch.

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Where does fabric help and where does it hurt?

The distinction is whether the covering material decomposes. Inert coverings pair well with fabric; organic ones do not:

Application	Use fabric?	Why
Gravel path or dry riverbed	Yes	Separation layer; stone stays out of the soil
Paver or flagstone base	Yes, under the base course	Prevents subgrade mixing; protected from UV
Stone-mulched shrub bed	Usually yes	No organic layer builds up
Bark or wood-chip planting bed	No	Mulch decomposes into a weed seed bed
Vegetable or annual bed	No	Constant replanting; soil health matters most
Slope with loose mulch	No	Mulch slides on the fabric surface

Close-up detail of the material being worked in a landscaping & hardscaping project, in warm late-afternoon light

What goes wrong in the first five years?

A predictable sequence. Year one looks excellent and almost no weeds appear. By year two, mulch has begun breaking down and a thin organic layer covers the fabric. By year three, weeds are established in that layer and their roots have knitted into the weave, so pulling them lifts and tears the fabric. Somewhere in years three to five, edges start appearing at the surface where mulch has thinned, the exposed material goes brittle in UV, and the bed becomes noticeably harder to work in because a spade or a bulb planter now meets plastic. Repairing it usually costs more effort than never installing it did.

Wide view of a person laying a stone paver into a sand base while building a garden path, in soft early-morning light

What does it do to the soil?

It interrupts the cycle that makes a mulched bed improve over time. In an unfabric bed, mulch decomposes at the soil interface, earthworms and soil organisms pull that organic matter down, structure improves and water infiltrates better each year. A fabric layer physically separates the two, so the soil below receives little new organic matter and often becomes compacted and biologically poorer. That is the reasoning behind the advice from university extension horticulture programs to skip fabric in ornamental beds and rely on mulch depth instead.

Three-quarter view of a person laying a stone paver into a sand base while building a garden path, in soft overcast light

What should you do instead?

Three inches of mulch, maintained. That depth blocks light from most annual weed seeds, which is the entire mechanism of any weed barrier, and it feeds the soil as it breaks down. Before mulching, remove perennial weeds by the root, since nothing short of removal stops bindweed, quackgrass or thistle. For a stubborn area, sheet mulch: lay overlapping cardboard, wet it thoroughly, and cover with 3 inches of mulch. It smothers existing growth, then disappears. Top up mulch annually to hold the depth, and expect a small amount of hand weeding, which takes minutes in a bed with no fabric and is miserable in one with fabric.

For lifespan figures, see how long landscape fabric lasts and how long it lasts under gravel. If you are choosing a path surface, gravel versus mulch paths compares them. The consensus picks are in our best landscape fabric roundup, and bed boundaries are covered in the best landscape edging. More in the landscaping and hardscaping hub.