How to Line a Wooden Planter: Materials, Steps and Mistakes

Yes, you should line a wooden planter, and the best way is to line the sides and leave the base open for drainage. Use breathable landscape fabric if you want the easiest, safest option, or heavy plastic with drainage holes cut to match the planter’s own if you want maximum protection for the timber. Staple the liner just below the rim, press it into the corners and let water escape freely at the bottom. This guide walks you through the choice, the method and the small details that stop a liner doing more harm than good.

TL;DR

• Line the inside walls of the planter. Keep the base open, or cut drainage holes in the liner that line up with the holes in the wood.
• Landscape fabric is the forgiving choice because water passes through it. Heavy plastic protects the wood more fully but only works if it drains.
• For fruit and vegetables, choose an inert liner such as a heavy-duty membrane or EPDM, and avoid tar-based products and conventional sealers.
• Treat the outside of the timber with a suitable preservative or paint, and let it dry fully before you plant.
• A liner is cheap to fit once and expensive to forget: soil held against bare wood is what rots a planter from the inside.

Table of Contents

• Why you should line a wooden planter
• Choosing what to line a wooden planter with
• How to line a wooden planter, step by step
• Growing edibles in a lined wooden planter
• Common mistakes to avoid
• When to replace the liner
• Our view on lining wooden planters
• Find your next planter
• FAQ
• Sources

Why you should line a wooden planter

Wood and wet soil are not natural partners. The RHS Advice Team says wood rots over time, but lining a wooden container with an old compost bag and punching holes in the base can extend its lifespan. The reason is simple moisture. Timber that stays wet swells, and according to Safeguard Europe, once water fills the internal cavities above roughly 30% moisture content, the wood can swell, warp and crack, which lets the fungi behind rot penetrate deeper.

A planter is about the worst-case environment for timber: damp compost pressed against the boards all season, with no chance to dry out. A liner puts a barrier between the two. It also does a second job that people forget. Fabric also stops soil escaping through any wide gaps between boards, which matters for planters made from decking, pallets or slatted boards.

Do all wooden planters need one?

Not all wood is equal. Untreated pine and fir boxes benefit most from a liner because bare softwood soaks up moisture quickly. Naturally rot-resistant woods such as cedar hold up longer unaided, though the same source says a liner still extends their life and keeps soil from staining the inside faces.

If your planter is pressure-treated, it has a head start. Thorndown Paints notes that pressure-treated timber is protected against rot and fungi for up to 15 years, but the treatment does not protect against weather and UV fade, and water remains the main cause of damage. In practice, a liner and a coat of paint or stain on the outside work well together.

A quick rule of thumb:

• Untreated softwood or a homemade planter: line it.
• Pressure-treated planter: lining is optional but sensible, and it is the simplest way to keep soil off the timber if you are growing food.
• Hardwood planter that you have already oiled or sealed: a liner adds protection for the interior faces, where oil is hardest to maintain.

Choosing what to line a wooden planter with

There are three main families of liner. Each has a place, and the right one depends on what you are growing and how long you want the planter to last.

1. Landscape fabric (geotextile)

This is the easy default. Because it is water-permeable by itself, there is less risk of trapping moisture even if you do not perforate it perfectly. Water drains through, soil stays in, and the wood is kept from direct contact with wet compost. The Spruce recommends porous landscape fabric precisely because it lets water drain while keeping wet soil off the wood.

The trade-off is that fabric is more breathable, so it lets the compost dry out slightly faster than plastic does. BBC Gardeners’ World Magazine puts it simply: plastic keeps in moisture, whereas fabric is more breathable. In a hot summer, that means a little more watering for thirsty plants.

Lifespan: the same fabric guide expects landscape fabric to last roughly 2 to 4 growing seasons in full sun before it thins and tears. That is plenty for most bedding and herbs, and it is easy to replace when you next refresh the compost.

2. Heavy plastic sheeting, compost bags and damp-proof membrane

Plastic gives the most complete barrier. The RHS advises lining the inside with old bags or other recycled plastic sheeting to prevent leaching into the soil when using preservative-treated wood. Gardeners’ World Magazine lists heavy-duty plastic sheeting, old compost bags, a pond liner or landscaping fabric as options for a pallet planter.

One UK build shows how a thick membrane can be used well. In a decking planter described by Homebuilding, the sides and back were lined with 300MU damp-proof membrane made from recycled polyethylene, while horticultural fleece went at the base for drainage, with rubble below. That is a neat pattern: solid plastic where the wood is most exposed, something porous where water needs to leave.

There is a small advantage to plastic as well. A plastic liner helps keep water in the soil reservoir and protects the wooden container from rotting, which suits plants that like consistently moist soil. Heavy plastic sheeting is typically expected to last 3 to 5 seasons.

If you want to keep costs close to zero, a recycled bag is one of the simplest low-cost lining methods to reuse what you already have. Just choose a thick one, because thin carrier bags tear when you pack in compost.

3. Pond liner and EPDM rubber

For a planter you want to last, or for edibles, rubber is the premium option. EPDM liners are tough, flexible, UV-resistant and inert for edibles, and they can last decades when protected from sharp edges. Woodworking Advisor suggests a rubber pond liner regularly lasts 10 years or more. PVC and HDPE liners are cheaper and puncture-resistant but can be stiffer, so choose a thicker gauge for large planters to reduce wrinkling at the corners.

Quick comparison

Lifespans are guides from one source and depend on sunshine, sharp edges and how carefully the liner is fitted.

How to line a wooden planter, step by step

1. Check the drainage first

Before a liner goes in, look at the base. A planter with no holes will hold water however good the liner is. A hands-on UK walkthrough on lining a planter box starts with exactly this: if the box has no drainage holes, drill some evenly across the base, because otherwise water sits on the plastic and creates very poor growing conditions.

If you need to add holes, our guide to drilling planter drainage holes safely covers the drill size and spacing, and planter drainage options explains what helps and what only looks as if it helps.

2. Treat and dry the timber

If the wood is untreated, the RHS says it can be painted with a preservative to extend its lifespan. Do this to the outside and the top edges while the planter is empty, and give it the full drying time on the tin. Any liner should go into dry timber, not damp.

If you will be growing food, choose carefully. The Spruce warns that conventional wood sealers usually contain chemicals that can release into potting soil, and describes water-based preservatives based on boron salts as considered safe. Boiled linseed oil is a common choice, but one permaculture source notes it contains metallic salts that can leach into the soil, so keep it to the outside and away from interior faces that touch the soil or edible plants.

3. Measure and cut the liner

Measure the depth and perimeter of the inside, then add an allowance for the corners and a few centimetres over the rim. It is better to cut it slightly generous and trim later. For a long planter, one strip around the walls is easier than separate panels, because there are fewer seams where soil can escape.

4. Fit it into the corners

A tidy trick from the UK how-to is to lay the sheet across the top and push it gently down into the box, rather than forcing it from the sides. Work into each corner and fold the surplus into a flat pleat rather than a bulky crease. With thicker membrane or EPDM, allow a little slack so the weight of compost does not stretch the liner tight against the corners and stress it.

5. Staple it just below the rim

Use a staple gun or tacks every 10 to 15 cm, keeping the fixings just below the top edge so that they are hidden by compost. Trim the excess so that no plastic shows above the soil line. Rust-resistant staples are worth the pennies.

6. Make the drainage work with plastic

This is where most plastic-lined planters go wrong. A solid liner across the base creates a bathtub. The safest approach is one of two:

• Line the sides only. This is the approach in the Homebuilding build, with a porous fleece at the base. The water exits through the bottom, but the wet soil never touches the walls.
• Line the base too, then cut matching holes. Woodworking Advisor says solid plastic only works safely if you cut drainage openings that line up with the box’s own drainage holes. Push a screwdriver or sharp pencil through the plastic from inside, using each hole in the wood as the guide, and widen it with scissors if the plastic closes up.

A layer of rubble or gravel in the base, as in the decking build, gives the water somewhere to go before it reaches the holes, and keeps compost from blocking them. Do not use it as a substitute for holes.

7. Fill, firm and water in

Add compost in layers, firming gently, and water thoroughly. Watch the first soaking. If water runs out of the base within a minute or two, the liner is doing its job. If it pools on top, check the holes again. If you are unsure how much compost the planter takes, our planter soil volume guide saves you a second trip to the shop.

Growing edibles in a lined wooden planter

This is the question that makes people hesitate, so it deserves clear answers.

Is treated timber safe? According to Netmums, modern pressure-treated wood uses copper-based preservatives, arsenic-containing treatments stopped being used in domestic settings over 20 years ago, and many advisers now accept ground-contact-rated copper-treated timber for edible beds. The same article says that if you are still wary, you can line the inside faces with a heavy-duty membrane or geotextile so the soil never touches the timber directly. That is a straightforward reason to line a planter for vegetables.

Which liner suits edibles? Pick inert materials. For edible planters, EPDM is inert and suitable, and you should avoid bitumen, tar-based products and heavy-metal pigments that can leach into the soil. If you use any sealant or coating, choose products with food-contact ratings.

What about sun? Houzz notes that plastic liners may not make sense for growing vegetables in full sun where leaching could be a risk. If your planter sits on a south-facing patio, geotextile or EPDM are the calmer choices.

If you are deciding between a planter and something larger for crops, our comparison of planters versus raised beds will help you choose the right scale.

Common mistakes to avoid

1. Sealing the base without holes. The number one cause of soggy roots in a lined planter.
2. Using thin carrier bags. They split under the weight of wet compost. Use compost bags, damp-proof membrane or a proper liner.
3. Lining over damp or freshly painted wood. Trapped moisture and solvents defeat the point. Let everything dry.
4. Letting the liner show above the soil. It looks untidy, and sunshine degrades exposed plastic faster. Trim it back below the rim.
5. Standing the planter flat on the ground. Raise it on feet or a stand so air can circulate underneath and the base can dry. Our planter stands guide has options to buy or build.
6. Skipping the outside. A liner protects the inside. The outer faces still need paint, stain or preservative to resist rain and UV.

When to replace the liner

Most liners are out of sight, so build a habit: when you empty the planter at the end of the season, or when you replace the compost, look at the liner. Fabric that has thinned, torn or become brittle should be changed. Plastic that has gone stiff or split at the corners needs replacing too. Check the timber behind it while you have it open. Soft, dark or crumbly patches are a sign that moisture got through somewhere. Dry it, treat it and refit a new liner before you fill.

Our view on lining wooden planters

We sell a wide range of wooden and other garden planters, and the thing we see time and again is that the best-looking planter is the one that has been looked after on the inside.

Our advice is simple. Choose a planter with real drainage holes. Line the walls with fabric or a thick membrane, keep the base open, and raise the whole thing off the ground. It costs very little, takes an afternoon, and gives the timber many more seasons.

If you are buying new, think about where it will sit and what you will grow in it. A herb planter by the kitchen door needs different treatment from a large trough of summer bedding at the end of the garden. Start with the plants, then choose the planter and liner to suit.

Peter

Find your next planter

If you are ready to replace a tired planter or add a new one, browse our range of outdoor pots and planters in a variety of sizes and styles to suit patios, balconies and borders. We offer free delivery on orders over £70, easy returns within 14 days and next-day delivery options, so you can have the planter and be lining it within days.

For everything else that makes outdoor space more comfortable, from bistro sets to chimeneas, take a look at the full Great Gardens Online range.

FAQ

Should you line a wooden planter?

In most cases, yes. A liner keeps wet compost off the timber, which is what causes rot from the inside. It is most useful for untreated softwood and homemade planters, and it is a sensible extra on treated timber if you are growing vegetables.

What is the best liner for a wooden planter?

Landscape fabric is the easiest all-round choice because water passes through it. Heavy plastic or damp-proof membrane suits thirsty plants if you cut drainage holes. EPDM pond liner is the most durable, and it is an inert choice for edible crops.

Should the liner cover the sides, the base or both?

Always cover the sides, as that is where soil presses against the wood. The base can be left open with a porous fleece and some gravel, or lined with holes cut to match the drainage holes in the planter.

How do you waterproof a wooden planter?

Treat the outside with a suitable wood preservative, paint or stain once the timber is dry, and line the inside with fabric, membrane or rubber. For edibles, use products suitable for food-growing and keep oil-based treatments off the interior faces. Keep the planter off the ground so the base can dry.

Can I use a plastic bag to line a planter?

A thick compost bag works well, as the RHS suggests, provided you punch holes in the base for drainage. Thin carrier bags tear easily, so save them for something else.

Sources

• RHS Advice: Growing plants in containers
• RHS Advice: How to make a raised bed
• Safeguard Europe: Waterproofing wood treatments in the garden
• The Spruce: DIY tips for wooden container planters
• Woodworking Advisor: How to line wooden planter boxes
• Thorndown Paints: Outdoor paint for timber planters
• BBC Gardeners’ World Magazine: How can I line my homemade planter?
• Homebuilding: Leftover decking garden planter
• Houzz: Using a wooden crate as a planter box
• Netmums: Timber for raised beds in British weather
• Deep Green Permaculture: Preserving timber raised beds with linseed oil
• DIY Garden: How to line a wooden planter box
• Klimaplanter: Low-cost lining methods

Recommended

• Planter Drainage Options: What Works and What Doesn’t
• Planter Soil Volume: How Much Compost You Need
• Forget to Water? Terracotta vs Plastic Planters for Home Gardeners
• 6 Safe Steps to Drill Planter Drainage Holes for UK Gardens