Why cedar earns its place in the British garden

Cedar has a quiet reputation among joiners and furniture makers, and for good reason. The timber is naturally resistant to rot, holds its shape well and weighs far less than oak, so a cedar bench can be moved by one person when the lawn needs cutting. Its oils deter insects and slow the spread of fungal decay, which matters enormously in a country where timber spends half the year damp.

That said, cedar is not magic. The durability lives in the heartwood – the darker, denser inner wood – while the pale outer sapwood has very little resistance to decay. A cheap cedar table built largely from sapwood may disappoint within three or four winters, whereas well-chosen heartwood can give fifteen years or more with modest care. Mild, humid British weather is kind to plants and brutal to timber, so the grade you buy matters more here than it would in a drier climate.

Know your grades before you buy

Cedar is usually sold in named grades, and understanding them saves both money and disappointment.

• Clear grade: almost knot-free, straight-grained and almost always heartwood. Beautiful for table tops and visible slats, but the priciest option.
• Architectural or knotty grade: tight, sound knots and some colour variation. Excellent value for benches and frames, provided the knots are firmly fixed rather than loose or cracked.
• Utility grade: mixed heartwood and sapwood, more shakes and splits. Fine for compost bins, hidden battens or temporary planters – not for a seat you want to keep.

When you inspect timber in person, look at the end grain: creamy white edges mean sapwood. Check for splits running in from the ends, resin pockets and any soft, spongy patches. Straight, even grain with closely spaced growth rings usually signals slower-grown, more stable wood. Homegrown cedar and cypress can be lovely, but ask how long it has been seasoned – poorly dried stock will twist as soon as it meets a wet autumn.

Matching grades to benches, tables and planters

Benches take the most punishment. Use clear or good knotty grade for seat slats around 20–25mm thick, set with a 6–8mm gap so rain drains instead of pooling. Legs and rails can be a lower grade at 45mm square, since thickness buys durability. Avoid knots on the front edge of a slat where hands rest and splinters form.

Tables need stability above all. A clear-grade top, ideally slatted rather than a single wide board, will stay flatter and shed water faster. If you prefer a solid top, choose narrow boards joined with a slight gap and seal the end grain thoroughly.

Planters are the hardest test because the timber stays permanently wet. Choose heartwood, use stock at least 25mm thick, and raise the base on feet so air moves underneath. A breathable liner helps keep soil away from the wood without trapping moisture against it.

Foundations, fixings and airflow

Most premature rot starts where wood touches soil or paving. Set furniture on adjustable feet, rubber pads or small paving slabs, leaving a 20–25mm clearance beneath. Give horizontal surfaces a very slight fall so water runs off rather than sitting in shallow pools.

Fixings matter too. Use stainless steel or hot-dip galvanised screws and bolts – ordinary mild steel rusts and stains the timber with black streaks that are difficult to remove. Pre-drill near the ends of boards to prevent splitting, and cup washers under bolt heads spread the load on softer cedar.

Protecting the timber from damp British weather

Untreated cedar will gradually weather to a soft silver-grey, which many people love. The trade-off is surface checking – fine cracks that open as the timber repeatedly swells and dries. If you want the original colour, or simply want the furniture to last longer, a finish is worthwhile.

• Choose a breathable oil or wood preserver rather than a film-forming varnish or thick polyurethane. Varnish traps moisture inside and then peels in sheets once damp gets behind it.
• Re-oil horizontal surfaces every spring, and vertical surfaces every second year. A quick test: if a drop of water soaks in within a minute, it needs another coat.
• Seal cut ends and drilled holes as you work, since end grain absorbs water like a straw.
• Clean algae and green mould with a soft brush, warm water and a little mild soap. Avoid pressure washers, which fray the grain and drive water into joints.
• Use breathable covers in winter, or none at all. Heavy plastic tarps seal in condensation and cause more harm than open exposure.

A simple seasonal routine

Spend twenty minutes on your cedar each spring and it will repay you for years. Check for loose fixings and tighten them. Sand away any raised grain or splintering with fine abrasive, always working along the grain. Clear fallen leaves and debris from beneath benches and planters, since damp leaf litter is where rot begins. Bring cushions and parasols indoors for the winter, and store furniture in a dry shed if you have the space – though cedar left out in the open, properly finished and raised off the ground, will cope perfectly well with a British winter.