How the two differ in kind
Landscape fabric is sold as the permanent answer to weeding and, in a planted bed, it is usually the wrong one. The reason is not controversial once it is stated plainly.
Weeds in a mulched bed do not mostly come up from the soil beneath. They arrive as SEED, on the wind and from birds, and they germinate in the layer at the top — which is the mulch, sitting ON the fabric. Their roots then grow down through the weave and into the soil below, and at that point the fabric is working against the gardener rather than for them: the weed cannot be pulled cleanly because its roots are locked into the fabric, so it tears off at the collar and regrows.
At the same time the fabric is preventing the thing mulch is actually for. Organic mulch is supposed to break down into the soil, feeding the soil organisms that build structure, hold water and make nutrients available. A fabric between the mulch and the soil interrupts that transfer, so the mulch rots on top of a barrier and the soil beneath slowly degrades — compacting, losing organic matter, and becoming harder and less hospitable to the plants the bed was made for.
MULCH DEPTH is the mechanism that actually suppresses weeds, and it works by excluding LIGHT: a sufficient depth of coarse organic material means most seeds either fail to germinate or exhaust themselves before reaching the surface. It also moderates soil temperature, reduces evaporation and, unlike the fabric, improves the soil continuously.
That mulch is consumed and has to be topped up is the system working, not failing — the material has gone where it was meant to go.
FABRIC has a real job, and it is a different one: SEPARATION under aggregate. Beneath a gravel path, a drive or a decorative stone area with no planting, it keeps the stone from working down into the soil and the soil from pumping up into the stone. There is no organic layer for seeds to colonise and no soil being improved, so the objections above do not apply.
The factors that actually differ
Show
| Landscape fabric | Mulch depth | |
|---|---|---|
| What it does | Separates two layers, and blocks light from below. | Excludes light from the soil surface, and decomposes into the soil. |
| Where the weeds come from | Mostly from seed landing ON TOP — which the fabric does nothing about. | Same, and depth is what stops them establishing. |
| Effect on weeding | Makes it HARDER — roots lock into the weave, so weeds tear off and regrow. | Easier. Weeds rooted in loose mulch pull out whole. |
| Effect on the soil | Negative over time. It interrupts the organic matter reaching the soil. | Positive and cumulative. It is how the soil is fed. |
| Life | Degrades, tears at every planting hole, and works its way to the surface as an eyesore. | Consumed and topped up, which is the mechanism working rather than failing. |
| Planting through it | Every new plant is a cut, and every cut is an opening. Beds change; fabric does not. | No obstacle. Pull the mulch aside, plant, push it back. |
| Where it genuinely belongs | Under aggregate — gravel paths, drives, stone areas with no planting. | Any planted bed, around trees and shrubs, and over bare soil generally. |
| Water and air | Permeable when new; blinds with fines over time, which can shed water rather than pass it. | Passes water readily and improves infiltration as structure develops beneath it. |
| Removal | Difficult and unpleasant once it has fragmented and roots have grown through it. | Nothing to remove. |
| Against perennial weeds | Ineffective. Bindweed, couch and horsetail come through or along it. | Also ineffective alone — these need removing rather than covering. |
Which one, and when
Choose landscape fabric when…
- Under gravel, stone or aggregate where nothing is planted — the separation job it is actually good at.
- Beneath a path or a drive, keeping the sub-base and the subgrade from mixing.
- As a temporary covering over ground being held for later work.
- Under a permanent surface that will not be planted, cut into or lifted.
Choose mulch depth when…
- Any planted bed, where suppression comes from depth and the soil benefits from the material.
- Around trees and shrubs — kept clear of the trunk and the root flare, which mulch must never bury.
- Where soil improvement is wanted as well as weed suppression, which is nearly always.
- Where the planting will change, since mulch accommodates that and fabric does not.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Why do weeds appear on top of landscape fabric?
- Because that is where the seed is and where the growing medium is. Weed seed arrives continuously on the wind, in bird droppings, in the mulch itself and on tools and boots, and it lands on the surface. In a fabricked bed the surface is a layer of mulch or gravel that collects dust, leaf litter and fine organic debris over a season or two, which is a perfectly serviceable seedbed. The seeds germinate there, and their roots grow downward through the fabric's weave into the soil below, anchoring them. So the fabric does not reduce the number of weeds arriving; it changes what happens when you try to pull one out, because the root is threaded through the fabric and the top breaks off. The plant then regrows from what is left.
- How does mulch depth actually suppress weeds?
- By excluding light and by exhausting the seedling before it reaches it. Most weed seeds are small and carry only enough stored energy for a short push toward the surface, and many species require light to trigger germination at all — so a sufficient depth of coarse material both prevents that trigger and outruns the seedling's reserves. The depth matters more than the material: too shallow and seeds germinate through it, too deep and it can starve the soil of air and hold excessive moisture against stems. Coarse, chunky mulches work better than fine ones because they let air and water through while staying loose, and because they resist forming the dense mat of decomposed fines in which new seed will happily germinate.
- Does fabric harm the soil?
- Over time, yes, by interrupting the exchange the soil depends on. Healthy soil structure is built from organic matter arriving at the surface and being drawn down and processed by earthworms, fungi and the rest of the soil biology, and that traffic is what creates the pores that hold air and water. A fabric layer between the mulch and the soil interrupts it: the organic material decomposes on top of the barrier instead of entering the soil, and the soil beneath receives progressively less. The result after some years is a bed whose soil is harder, lower in organic matter and less able to hold water than it was, under a barrier installed to make it easier to look after. It is a slow effect, which is why it is rarely connected to its cause.
- When is landscape fabric the right choice?
- Where its job is SEPARATION and nothing is planted. Under a gravel path, a stone drive or a decorative aggregate area, a geotextile stops the stone migrating down into the soil and the soil pumping up into the stone under traffic, which preserves the layer's depth and its appearance. That is a mechanical function, it is what geotextiles are engineered for, and the objections about weeds and soil do not apply because there is no organic layer for seeds to colonise and no soil being improved. It is also useful as a temporary cover on ground being held between phases of work. The distinction is simply whether anything is growing there: if it is a bed, it is the wrong product.
- What about fabric under decorative gravel in a planted bed?
- That is the hybrid that disappoints most reliably, because it is subject to both problems at once. The gravel accumulates wind-blown dust and organic debris and becomes a seedbed within a couple of seasons, so weeds germinate in it and root through the fabric exactly as they do through mulch. Meanwhile the planting requires cuts in the fabric, and each cut is an opening that enlarges as the plant grows and as the fabric degrades. The gravel also works its way through and under the fabric at the edges and at every disturbance, so the neat separation the fabric was installed to maintain is lost anyway. If gravel is wanted around plants, the honest expectation is periodic weeding and periodic topping up, with or without the fabric.
- How deep should mulch be, and can it be too deep?
- Deep enough to exclude light, and yes, it can easily be too deep. Beyond a certain depth the mulch begins to work against the plants it surrounds: it holds excessive moisture at the surface, restricts gas exchange to the roots, and encourages roots to grow up into the mulch layer where they dry out. The most damaging version is mulch piled against a trunk — the volcano of material heaped around a tree — which keeps the bark permanently wet, invites rot and rodent damage, and can kill a tree slowly. Mulch is kept clear of trunks and stems, with the root flare visible, and topped up to restore depth rather than added on top of what is already there without checking what depth is actually present.
- Does mulch rob nitrogen from the soil?
- At the interface, briefly, and it is mostly overstated for surface mulch. The organisms breaking down high-carbon material such as wood chips draw nitrogen to do it, which can produce a temporary deficiency in the thin zone where the mulch meets the soil. Applied as a surface mulch that zone is shallow and the effect on established plants rooted well below it is small, and the nitrogen is released again as decomposition completes. The situation that genuinely causes a problem is high-carbon material dug INTO the soil, where the depletion occurs throughout the root zone. The practical rule follows: woody material goes on top and stays there, and anything being incorporated into the soil is composted first.
- What works against perennial weeds?
- Removal, because neither fabric nor mulch is a solution to a weed that regenerates from its roots. Bindweed, couch grass, ground elder and horsetail store enough energy below ground to push through a mulch layer, and they travel laterally along or beneath a fabric and emerge at its edges and at every cut. A bed cleared of annual seed but left with perennial root fragments will be recolonised regardless of what is laid on top. The effective sequence is to eliminate the perennials first — by persistent digging out, by exhausting them with repeated cutting, by a long light-excluding cover of an opaque sheet for a full growing season, or by targeted treatment where that is acceptable — and only then to mulch, which is very good at keeping a clean bed clean.