Oak, Larch or Cedar? The Truth About Timber That Lasts Through a British Winter

There's a question we get most Saturdays, usually from someone stood in the yard clutching a scrap of paper and a phone photo of a fence that used to belong to somebody else. What's the best timber for outside?

The honest answer is that there isn't one. There's the right timber for your job, your budget and your tolerance for maintenance. And then there's the board that looks a bargain in March and looks thoroughly sorry for itself by the following February.

So here's the version we'd give you if the yard was quiet and the kettle had boiled. Five species, judged the way we judge them — by how they behave after ten wet winters, not how they look on the day you buy them.

Start with the number that actually matters

Every timber sold for outdoor use carries a durability rating, from Class 1 (will comfortably outlive the mortgage) down to Class 5 (barely worth the screws). Two things catch people out.

First, the rating describes heartwood — the dark stuff in the middle — not the pale sapwood round the edge. Bargain oak and bargain larch are so often bargain because there's a lot of sapwood in the pack. Second, a durable species laid flat on wet ground with no air around it will still rot. Rot needs water and still air. Take away either one and you've bought yourself a decade.

The five contenders, warts and all

European oak

Class 2, dense, and about as close to a sure thing as you'll find. This is what we'd specify for gate frames, a bench that never comes indoors, or anything structural you'd rather not think about again. It silvers off handsomely outside, which suits some gardens and not others.

The straight talk: green oak is cheaper, but it moves — a lot — so if you're cutting tight joints, buy air-dried and let it sit in the garage for a fortnight first. And check what you're actually being sold. 'Oak' on a price list is not a species name.

Larch

British larch sits around Class 3, Siberian a shade better, and it's the value pick for featheredge, fence rails and cladding. Resin, tight grain, decent life. What it isn't is a magic post. A slim, sappy larch post set straight into wet clay will be a wobbly larch post in six or seven years.

The straight talk: buy it thick, buy heartwood, and keep it out of standing water. Do that and it earns its keep.

Douglas fir

Strong, stiff, holds a screw properly, Class 3 to 4 depending on grade. Genuinely good for pergolas, raised bed frames and the skeleton of an outdoor bench. It's a structural timber first and a pretty timber second.

The straight talk: don't bury it. Douglas fir in open air is fine. Douglas fir in soil is a slow goodbye.

Western red cedar

Class 2, lightweight, stable, and it smells like a cedar chest — which is a daft reason to like a wood and also a perfectly good one. It's what we'd choose for cladding, garden furniture you'll move about, and anything you want to lift on your own.

The straight talk: it's soft. It dents. That's the trade for a board that shrugs off weather, and given the choice between a dent and a rot patch, we know which we'd take.

Thermally modified ash

Ash cooked at high temperature until the sugars fungi feed on are gone. The result is dark right through, very stable, and a genuinely good decking and furniture board. It takes an oil finish beautifully.

The straight talk: it's brittle. Pre-drill everything, particularly within 50mm of an end, or you'll be looking at splits. It is not a structural timber, and the treatment doesn't make it maintenance-free — it still wants a coat of something once a year.

Match the species to the job

The job	What we'd sell you	What we'd steer you past
Fence posts	Oak, or pressure-treated softwood at 100mm plus	Thin larch, anything sappy
Featheredge and fence boards	Larch, treated softwood	Untreated spruce bargains
Cladding	Cedar, larch, thermowood	Thin-section oak that'll cup
Decking	Thermally modified ash, cedar, treated pine	Boards under 25mm thick
Garden furniture	Oak, cedar, thermowood	Douglas fir left out all year
Raised beds	Douglas fir, oak	Anything with an unknown finish on it
Pergola and structure	Douglas fir, oak	Thermowood — too brittle in long spans
Edging and retaining	Oak, larch heartwood	Sapwood-heavy anything

What recent winters are telling us

The pattern across the last few years has been mild and wet rather than cold and crisp, with the occasional storm thrown in for good measure. That matters more than most people think, for three reasons.

• Mild, damp winters are fungal weather. A hard frost slows rot down; a wet January at nine degrees does the opposite.
• We're getting more wet–dry cycling, and that's what cracks and lifts a finish. A film-forming coating will fail faster than an oil that lets the timber breathe.
• Ground stays saturated for longer. If you're setting posts, go up a size, stand them on a gravel shoe rather than a fully sealed concrete collar, and make sure water has somewhere to go.

A north-facing fence in Manchester is a different job from a south-facing one in Kent, and we'd rather you told us which you've got.

Things we'll talk you out of

If you come in for a cheap treated post and ask us to cut it in half, we'll ask whether you've got end-grain treatment for the fresh cut. Untreated cut ends are where posts fail first. Same story with bargain oak showing pale edges, and with any board described only as 'outdoor' with no species on the label. We'd rather sell you less timber that lasts than more that doesn't.

The cheap board usually isn't

A softwood post at a tenner that needs replacing in seven years costs more than an oak post at twenty-odd that doesn't — and that's before you count the Saturday you spend digging the old one out of the ground. Work out cost per year, not cost per metre, and the yard's advice gets a lot easier to follow.

Come and look at the stock before you commit. Bring your measurements, bring a photo of the gap you're filling, and we'll tell you straight.