Search "raised bed liner" and you will get fifty opinions, half of them wrong. Some gardeners line every bed reflexively. Others call it unnecessary and wasteful. The truth is that lining a raised bed is sometimes essential, sometimes helpful, and sometimes actively counterproductive — and the answer depends entirely on what your bed is made of, what it is sitting on, and what lives underground in your area.
We have built beds with liners and without, on soil and on concrete, in gopher territory and mole-free zones. After testing multiple materials over multiple seasons, here is what actually matters — and what is just fear marketed by liner manufacturers.
When You Definitely Need a Liner
Pressure-Treated Wood
Modern pressure-treated lumber uses ACQ (alkaline copper quaternary) or CA-B (copper azole type B) preservatives. Both contain copper compounds that leach into soil, especially in the first 1–2 years and in acidic soil conditions. The EPA says current formulations are safe for raised bed gardening, and the copper concentrations measured in adjacent soil are low. But "low" is not "zero," and if you are growing food, there is no reason to accept any leaching when a $15 sheet of HDPE eliminates it. Line the interior sides of the bed. The bottom can remain open.
Concrete or Asphalt Contact
If your raised bed sits on a concrete patio, asphalt driveway, or other hardscape, line the bottom. Concrete leaches lime, which raises soil pH over time — not a disaster, but not ideal for acid-loving crops like blueberries and potatoes. More importantly, a bottom liner prevents staining on the concrete surface. Use landscape fabric here, not plastic — you still need drainage through the bottom.
Gopher and Vole Country
This is not a liner — it is armor. If you have pocket gophers or voles that tunnel into raised beds and eat roots, line the bottom with 1/2-inch hardware cloth (galvanized welded wire mesh) before filling with soil. This is non-negotiable in gopher-prone regions of the western US. Gophers can destroy an entire bed of root crops in a single night. Our raised bed building guide includes hardware cloth installation in the base construction steps.
Treated Landscape Timbers or Railroad Ties
Old-style treated timbers may contain creosote or CCA (chromated copper arsenate). If you inherited beds made from these materials and cannot replace them yet, line the interior completely — sides and bottom — with 40-mil HDPE or pond liner. Better yet, replace the timbers with untreated cedar or white oak as soon as your budget allows.
When You Do NOT Need a Liner
Untreated Cedar, Redwood, or White Oak
These species resist rot naturally through tannins and extractives in the heartwood. They do not leach anything harmful into soil. Lining the inside of an untreated cedar bed is unnecessary and can actually trap moisture against the wood, accelerating rot from the inside rather than preventing it. Let the wood breathe. It will last 10–25 years without a liner. Read our wood guide for species-specific lifespan data.
Metal Raised Beds
Galvanized steel and Corten steel do not leach anything concerning into soil. Zinc (from galvanization) is actually a plant micronutrient. The temperatures inside a metal raised bed in summer are not high enough to cause problematic zinc release. Do not line a metal bed — the liner serves no purpose and prevents the soil from contacting the metal surface, which is the only thing holding heat in spring (a benefit, not a problem).
Beds on Good Native Soil
If your raised bed sits on reasonable garden soil (not contaminated, not paved), leave the bottom completely open. Open bottoms allow earthworms to migrate up into the bed, roots to penetrate deeper than the frame, and water to drain naturally into the subsoil. A bottom liner — even landscape fabric — disrupts all three of these benefits.
Liner Materials Compared
If you have determined that your situation warrants a liner, choose the right material:
| Material | Best For | Cost (4×8 bed) | Lifespan | Drainage |
|---|---|---|---|---|
| Landscape fabric (woven) | Bottom lining on hardscape | $8–$15 | 5–10 years | Good (water passes through) |
| HDPE plastic (20–40 mil) | Side lining against treated wood | $15–$30 | 20+ years | None (must not cover bottom) |
| EPDM pond liner (45 mil) | Full containment on contaminated sites | $30–$60 | 20–30 years | None (drill drainage holes) |
| Hardware cloth (1/2") | Pest exclusion on bottom | $20–$35 | 10–15 years | Full (wire mesh only) |
Landscape Fabric
Woven polypropylene landscape fabric is the most common "liner" and the most commonly misused. It works well on the bottom of beds sitting on hardscape because it allows drainage while preventing soil from staining concrete. It does not work well as a side liner — roots grow through it, it tears when you dig near the edges, and it traps moisture against wood. Use it where drainage matters. Avoid it where chemical barrier matters.
Buy commercial-grade fabric, not the cheap stuff from the hardware store garden aisle. Commercial-grade is thicker (3–4 oz per square yard vs 1–2 oz), lasts longer, and resists root penetration better.
HDPE Plastic Sheeting
High-density polyethylene is the gold standard for chemical barrier. It is food-safe (the same material used in milk jugs and food containers), impervious to water and dissolved chemicals, flexible, and long-lasting. Use 20–40 mil thickness — thinner tears too easily during installation and soil filling. Line the interior sides of the bed, fold over the top edge by 1–2 inches, and staple to the outside of the frame. Leave the bottom open for drainage.
EPDM Pond Liner
Synthetic rubber, extremely durable, fish-safe (buy pond-grade, not roofing-grade which contains fire retardants). Overkill for most raised beds but appropriate if you are building on contaminated soil and need full containment. If you use pond liner on the bottom, drill 1/4-inch drainage holes every 12 inches to prevent waterlogging.
Hardware Cloth
Not a liner in the traditional sense — hardware cloth is 1/2-inch galvanized welded wire mesh that goes on the bottom of the bed to block burrowing pests. It does not block chemicals or soil migration. Install it flat across the bottom of the bed frame, fold the edges up 2–3 inches against the interior sides, and staple in place before filling with soil.
Common Mistakes to Avoid
- Using plastic on the bottom: Solid plastic on the bottom of a raised bed creates a bathtub. Water pools, roots rot, and anaerobic bacteria produce sulfur compounds that smell terrible and kill plants. Never seal the bottom unless you have drainage holes and are building on contaminated ground.
- Using cheap landscape fabric as a chemical barrier: Landscape fabric does not stop chemical leaching. Water passes through it — and dissolved chemicals ride along with the water. If you need a chemical barrier (treated wood, contaminated soil), use HDPE or EPDM.
- Lining cedar or white oak beds: Moisture trapped between a liner and untreated wood accelerates rot. You are spending money to shorten the life of your bed.
- Confusing hardware cloth with liner: Hardware cloth stops gophers. It does not stop chemicals, roots, or soil migration. These are different tools for different problems.
Building a new raised bed? Browse our raised bed kits in cedar and metal — no liner needed for either material. Skip the liner, save the money, and invest in better soil instead.
Frequently Asked Questions
Will a liner make my raised bed last longer?
A side liner can protect wood from constant soil moisture contact, potentially adding 2–5 years to a bed's lifespan. But this only applies to fast-rotting species like Douglas fir or untreated pine. Cedar, white oak, and metal beds do not benefit — and as noted above, a liner can actually trap moisture and accelerate cedar rot. If longevity is your goal, choose a rot-resistant material instead of trying to protect a cheap one with plastic. Our wood selection guide helps you choose the right species.
Is BPA a concern with HDPE liners?
No. HDPE (recycling code #2) does not contain BPA or phthalates. It is one of the safest plastics and is used for food and drinking water containers. If you see warnings about plastic liners and BPA, those refer to PVC (vinyl) products — never use PVC in a food garden. Stick to HDPE and you are fine.
Can I use cardboard instead of landscape fabric?
Cardboard on the bottom of a raised bed is fine as a temporary weed barrier — it suppresses grass and weeds for the first season while they die underneath. But it decomposes within 6–12 months, so it is not a long-term liner. Think of it as a weed killer, not a structural component. Remove tape and staples before laying it down.
What about using old carpet or tarps?
Never use carpet in a garden. Carpet backing contains latex, adhesives, flame retardants, and antimicrobial treatments — none of which belong near food crops. Tarps are typically polyethylene (safe) or PVC (not safe) — check the material before using. When in doubt, spend $15 on purpose-made HDPE and know exactly what you are getting.
Do I need to replace a liner over time?
HDPE and EPDM liners last 20+ years and do not need replacement unless physically damaged. Landscape fabric degrades in 5–10 years, especially the cheap grades — you will notice roots growing through it and the fabric tearing when you dig. Hardware cloth lasts 10–15 years before the galvanization wears through and the wire rusts. Budget for replacement when planning long-term bed maintenance.
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