How to Care for Pressure-Treated Timber
Pressure-treated softwood is the standard for outdoor joinery in Britain because the preservative is forced into the timber rather than brushed on to the surface. It does not stop the wood behaving like wood. This guide explains what to expect in the first year, what is normal, and the small amount of maintenance that makes a planter last.
What happens in the first twelve months
The colour changes
Fresh pressure-treated timber has a green or honey tone that fades. Left alone outdoors it drifts towards a soft silver-grey, usually within one to two seasons depending on how much sun and rain it gets. This is a surface effect and has no bearing on strength.
Small cracks appear
Timber takes up moisture in winter and gives it back in summer, and as it does the surface opens into short lengthwise splits. These are called shakes or checks. They run with the grain, they do not go through the board, and they are not a fault. A planter with a few surface cracks is behaving exactly as solid timber should.
Boards move slightly
A little cupping or a hairline gap between slats is normal seasonal movement. Our planters are built with battens and corner posts specifically so that the frame stays square while the boards do this.
The maintenance that actually matters
- Keep the base off standing water. This is the single most useful thing you can do. Our planters sit on short feet for exactly this reason. If yours is on a patio that puddles, move it or pack it up on a couple of slabs.
- Do not seal the bottom. Water has to be able to leave. Blocking the drainage is the quickest route to rot.
- Clear debris each autumn. Brush fallen leaves and soil off the top rail and out of the corners. Wet organic matter sitting against the grain holds moisture where you do not want it.
- Re-coat every two or three years if you want to keep the colour. An exterior wood oil or a breathable stain will hold a warmer tone. Choose a product that is described as suitable for pressure-treated timber and let the wood dry for a few days first.
- Do not use a film-forming varnish or a solid gloss paint. Anything that seals the surface completely will trap moisture underneath and eventually lift and flake.
- Do not pressure wash. A high-pressure jet tears the softer summer growth out of the grain and leaves a rough, fibrous surface that weathers faster. A stiff brush and water is plenty.
Should I re-treat the cut ends
Everything we build is cut and finished in the workshop, so you should not need to. If you ever cut into a pressure-treated board yourself, brush the exposed end with an end-grain preservative, because the deep treatment does not extend across a fresh cut.
What about the liner
Every planter leaves us with a permeable liner already fitted. It keeps compost off the inside faces while still letting water through. Leave it in place. If it ever tears, it is easy to replace with any permeable landscape membrane cut to fit.
Winter
Timber copes with frost perfectly well. The thing to avoid is a planter sitting in a shallow pool of freezing water all winter. If you can, lift it clear or move it to a spot that drains. Emptying is not necessary.
Our full care notes appear on each product page, and there is more about where our timber comes from on our timber sourcing and sustainability page.