Should You Line a Raised Bed? Sides, Base & Drainage

Illustration of vegetable raised beds with clear access paths

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Whether you should line a raised bed depends on what the bed is made from, where it sits, and what you plan to grow. The short answer is: do not line the base if the bed sits on open soil, when an impermeable liner would block drainage and root access. Line the sides only in specific situations, such as untreated timber treated with preservative, or masonry beds growing acid-loving plants. On hard surfaces, you need drainage holes in the sides rather than a liner.

Table of Contents

When to line the sides of a raised bed

Side lining is not a routine step for every raised bed. The RHS identifies two clear cases where lining the inside walls is useful.

Untreated timber with preservative

If you build a bed from untreated wood such as recycled pallets or scaffold boards, you may paint the outside with a preservative to extend its life. Use only a preservative explicitly suitable for the intended growing-bed application. A side lining may separate wood and soil but is not a guarantee against leaching and does not make unknown or contaminated timber suitable. This is particularly relevant if you are growing edible crops, because you do not want preservative chemicals moving into the root zone.

Masonry beds for ericaceous plants

Stone or brick raised beds contain lime in the mortar. If you plan to grow ericaceous (acid-loving) plants such as rhododendrons, camellias, heathers or blueberries, the RHS recommends lining the inside of the masonry with recycled plastic. This separates the lime from the plant roots and helps maintain the acidic soil conditions those plants need.

When you do not need to line the sides

New landscaping timber with a known treatment differs from old creosote-treated railway sleepers. Confirm that the particular product is suitable for its proposed use. RHS expert Leigh Hunt notes that new sleepers and treated wood are fine for edible crops without a liner. If you want to be extra cautious you can line with plastic, but the RHS points out that this is not desirable as we move away from using plastics. So for most new timber beds, side lining is optional rather than essential.

Recycled plastic sleepers and masonry beds used for non-ericaceous plants also do not require side lining. The key is to match the lining decision to the material and the plants, not to line every bed by default.

Base preparation: open ground versus hard surface

The base of a raised bed should almost always remain open to the soil below. An impermeable plastic base prevents water from draining downwards and stops plant roots from reaching the soil beneath. The RHS step-by-step guide for timber beds makes no mention of a base liner. Instead, it describes preparing the ground itself.

On free-draining soil

Clear persistent weeds and assess the ground below the bed. You may remove turf or use an appropriate no-dig preparation with biodegradable cardboard; do not confuse temporary cardboard with a permanent plastic liner. Loosen compacted soil only when workable. Preserve useful topsoil rather than excavating it solely because the frame exceeds 50cm. A layer of rubble does not create drainage where there is no outlet and reduces usable root depth.

On a hard surface

If you build a raised bed on paving, concrete or another hard surface, water cannot drain downwards. The RHS says to adjust the bed design instead of lining the base. For timber beds, drill plenty of holes in the sides of the bed to allow excess water to drain away. For stone or brick beds, leave gaps at 45cm (18in) intervals between the joints in the first two courses. Cover these gaps on the inside with fine wire mesh, and heap gravel against the mesh when filling the bed to prevent soil clogging the drainage openings.

In these conventional designs, the hard surface acts as the base and side outlets provide drainage. A purpose-made planter may use a different liner and outlet arrangement, so follow its complete installation design.

Drainage: the real reason lining decisions matter

Lining a raised bed incorrectly can create waterlogging, which is worse than no lining at all. The RHS is clear that raised beds should be built on free-draining ground wherever possible. If your garden soil is heavy clay and prone to waterlogging, a raised bed helps because the soil level is lifted above the surrounding ground, improving drainage. But if you then line the base, you undo that benefit by trapping water inside the bed.

For beds on hard surfaces, the RHS recommends a different soil mixture to improve drainage: three parts organic matter, four parts sharp sand and seven parts topsoil. This is more free-draining than the standard mix used on open ground. You should also be prepared to refresh and replace the soil regularly, as you would when repotting a large container, to maintain good drainage.

Side lining, where used, should not interfere with drainage. The plastic sheeting recommended for untreated timber or masonry beds is placed against the inner walls, not across the base. Drainage still occurs through the open base on soil, or through the side holes on hard surfaces.

Choosing lining materials

The RHS does not specify a particular brand or thickness of liner. It suggests using old compost bags or other recycled plastic sheeting for side lining. This is a practical, low-cost option that reuses material you may already have. For masonry beds with ericaceous plants, the same recycled plastic works to separate lime from roots.

For covering drainage gaps in masonry beds on hard surfaces, the RHS recommends fine wire mesh. This must be fine enough to hold back soil but open enough to let water pass through. Heap gravel against the mesh on the inside to further reduce clogging.

A permeable fabric is different from waterproof plastic, but it is usually unnecessary over healthy open soil and can restrict rooting or complicate later cultivation. Follow a specialist design if separating growing medium from a particular surface is necessary. If you are unsure whether to line, the default should be no base liner and side lining only for the specific cases described above.

Practical checks before you build

Check the ground. If the bed will sit on soil, remove turf and loosen the soil. If the soil is heavy clay, building the bed in late summer when the ground is drier will be easier.
Check the material. Check the known timber treatment and any specified liner. For acid-loving plants in masonry beds, isolate mortar appropriately while preserving drainage.
Check the surface. On hard standing, plan for side drainage holes or gaps before filling the bed. Do not rely on a liner to solve drainage.
Check the depth. Measure usable root depth after any designed base material is included; do not add unknown rubble simply as cheap filler.
Check the plants. Ericaceous plants in masonry beds need a plastic barrier. Most vegetables and ornamentals in timber beds do not need any side lining.

Lining a raised bed is a targeted fix, not a universal step. Keep the base open, line the sides only when the material or the plants demand it, and put your effort into drainage instead.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Recycled plastic sheeting or clean compost bags: A clean, suitable side liner can separate timber or masonry from growing medium when the design calls for one; it must preserve drainage. Use intact material intended for the application with a known history; do not rely on a liner to make contaminated timber or ground safe. Search Amazon for Recycled plastic sheeting or clean compost bags.
Fine wire mesh: Needed to cover drainage gaps in the first two courses of masonry raised beds built on hard surfaces, preventing soil loss while allowing water to escape. Check that the mesh is fine enough to hold back soil but open enough for water flow, and that it is rust-resistant for long-term contact with damp soil. Search Amazon for Fine wire mesh.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.