Should I put weed membrane under bark or gravel in a border?
In a planted border, no — it fails within three years and leaves a mess that outlasts the planting. The three places it genuinely belongs, and what to do instead.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 5 min
Short answer
In a planted border, membrane is a mistake. Silt and rotted mulch build a seedbed on top of it within two or three years and weeds root through the weave where you cannot pull them; perennial weeds use the planting slits; and worms cannot take organic matter down, so the soil stops improving. Use it under gravel paths and drives, and under permanent unplanted gravel. In a border, use a thicker mulch instead.
Landscape fabric is sold as the way to stop weeding forever and it works beautifully for about two years. What happens after that is predictable, well documented in every garden that has one, and almost impossible to reverse without lifting the entire border — which is why it is worth understanding the failure mode before you spend a Saturday laying it.
Step by step
- Understand what membrane actually stops.It blocks light to weed seed already in the soil and physically obstructs shoots coming up. That is genuinely effective, and in year one and two a membraned border is nearly weed-free.
- Understand what builds up on top of it.Wind-blown soil, leaf litter, and the fine material from the mulch as it breaks down. Within two or three years there is 20 to 40mm of perfectly good growing medium sitting on the fabric, and weed seed lands in it and germinates. Their roots thread through the weave, which means they cannot be pulled — the top snaps off and the root stays.
- Understand what comes up through the slits.Every plant you put in needs a cut in the fabric. Bindweed, couch grass and ground elder find those cuts, come up through them, and then run sideways underneath the fabric where you cannot see them, cannot hoe them and cannot dig them out.
- Understand what it does to the soil.Worms move organic matter from the surface down into the soil. A woven sheet stops that. Lift a membrane after five years and the soil beneath is pale, compacted and poor compared to an unmembraned border alongside — the one process that improves soil year on year has been switched off.
- Understand how it ends.The fabric degrades in UV where it is exposed and becomes brittle. When the border is eventually replanted it shreds into strips that tangle in forks and work up to the surface for years afterwards. Plastic-weave fabric never actually leaves the garden.
- Use it where it genuinely belongs.Under gravel paths and drives, where nothing is planted and the job is separating gravel from soil rather than suppressing weeds. Under permanent decorative gravel in an unplanted area. And as a temporary opaque cover laid on top of ground to kill off perennial weeds before planting, then removed.
- Use a deeper mulch in a border instead.Seventy-five millimetres of bark or composted woodchip suppresses annual weed seed almost as well as fabric in year one and gets better every year rather than worse, because the soil improves. Top it up annually and hoe the few weeds that appear.
- If you have inherited one, plan to take it out.It is a miserable job and it is worth doing. Lift the mulch, cut the fabric into strips around the plants, pull it out, and remulch. Do it in stages over a couple of seasons if the border is large.
Tips
- Fabric under gravel on a path or drive genuinely earns its place — it keeps the gravel out of the soil and the soil out of the gravel, which is a different job from weed suppression and one it does well permanently.
- Where you do lay it under gravel, use a woven geotextile rather than the thin black plastic sheet sold for borders. It lasts far longer and does not shred as readily.
- Weeds that germinate in the silt on top of gravel over membrane are the commonest complaint about gravel gardens. Regular light hoeing before they root through the fabric is the only practical answer.
- Plastic sheet with no permeability at all is worse than woven fabric in every respect — water cannot get through it, and the soil beneath goes anaerobic.
- A biodegradable jute or hessian mulch mat is a reasonable compromise for a newly planted shrub area. It suppresses weeds for two seasons and then rots away rather than becoming a permanent problem.
Alternatives
- A deeper organic mulch: Seventy-five millimetres of composted bark or woodchip, topped up annually. Suppresses annual weeds well, improves the soil rather than isolating it, and can be planted through freely.
- Dense planting: Ground cover and close spacing shade the soil so weed seed never germinates. It takes two or three years to close up and then it is permanent and free.
- Hoeing: A sharp hoe drawn just under the surface once a fortnight in the growing season kills weed seedlings before they establish and disturbs almost nothing. Ten minutes a border.
- Cardboard under a mulch: For a new bed, cardboard does the same light-exclusion job as fabric for a season and then disappears completely, leaving no permanent barrier.
Questions people ask
How long does membrane actually keep a border weed-free?
Two to three years in most gardens, depending on how quickly silt and leaf litter accumulate on top of it. Under a tree or a hedge it can be less than two.
Does it work better under gravel than under bark?
Yes, considerably — gravel does not break down into a seedbed the way bark does, so it takes much longer for a rooting layer to develop. It still eventually accumulates silt, and it still stops soil improvement.
Is there a fabric that does not fail this way?
Not in a planted border. The failure mode is not about fabric quality; it is about what accumulates on top and what cannot get through. Heavier woven geotextile lasts longer physically and fails in exactly the same functional way.