Building a Cedar Raised Bed for Strawberries

Why Cedar Earns Its Place

Cedar is the raised-bed timber that asks the least of you. Western red cedar and its close cousins carry natural oils that turn back fungal decay, so a cedar frame needs no stain, no oil and no plastic sleeve to survive a British winter. Treated softwood will outlast many gardeners, but it leaches copper or chromium salts into the soil around your plants, and the debate about food beds has never quite gone away. Cedar sidesteps the argument altogether. It weathers to a soft silver-grey if you leave it, holds a warm honey tone if you favour the new look, and it smells extraordinary when you cut it.

Built well, a cedar bed gives you fifteen to twenty years of service — three or four full rotations of strawberry planting, which is the timescale the crop actually works on.

Sizing, Siting and Depth

Strawberries are shallow-rooted in the wild, but they crop far harder in a deep, cool root run. Aim for a finished internal depth of at least 25 cm, and 30 cm is better. That is deeper than most shop-bought kits, which rarely clear 15 cm, and the difference shows in a dry August when shallow beds bake and the fruit shrivels.

For reach, keep the width to 1.2 m — you can tend plants from both sides without stepping on the compost. Length is your choice; 1.8 m to 2.4 m suits most plots. Site the bed in full sun, six hours minimum, and clear of the rain shadow cast by a wall or hedge. A gentle south-facing slope helps drainage, though level ground is perfectly workable.

• Timber: 45 x 150 mm cedar boards, two courses high
• Corner posts: 75 x 75 mm cedar, 60 cm long, set 20 cm into the ground
• Fixings: stainless steel screws, 70 mm, two per joint per course

Assembling the Frame

Cut the two long sides and two short sides, then mark the post positions at each corner. On soil, drive the posts in first with a spirit level against them — get the posts right and everything else follows. Screw the lower course of boards to the posts, check for level, then fit the upper course so the joints stagger.

Predrill cedar. It is softer than oak and splits readily when a screw is driven into end grain. A 4 mm pilot hole and a countersink takes seconds and saves a board. Where the frame sits on grass, skim the turf first and lay a strip of gravel under the boards to slow contact rot at the base.

Lining the Bed

Line the inside faces and the base with a permeable geotextile membrane, stapled to the timber. The word permeable matters: solid polythene turns a raised bed into a bath, and strawberries sitting in waterlogged compost rot at the crown faster than almost anything else will kill them. Woven membrane holds the compost in, lets surplus water drain away, and keeps soil off the wood so the cedar's own oils do their job undisturbed.

Leave the top 5 cm of liner unstapled until the bed is filled, then fold it down and pin it, hiding the raw edge. If your ground is heavy clay, add a 5 cm layer of horticultural grit beneath the lining to give water somewhere to go.

Filling With an Acidic Mix

Strawberries crop best between pH 5.5 and 6.5, so ericaceous compost is the sensible base. Build the fill from three parts ericaceous compost, one part leaf mould or well-rotted garden compost, and one part horticultural grit or sharp sand for drainage.

• Ericaceous compost: three parts — the acidic backbone
• Leaf mould: one part — moisture retention and slow feed
• Grit or sharp sand: one part — drainage and root aeration
• Feed: a handful of blood, fish and bone per square metre, worked into the top 15 cm

Fill to about 4 cm below the rim, so there is room to water without washing compost over the edge, and firm lightly as you go. Do not tread it down hard; you want structure, not concrete.

Planting and the First Season

Space plants 30 cm apart in staggered rows. Set each one so the crown — the fat growing point where the leaves emerge — sits exactly at compost level. Bury it and the plant sulks or dies; leave the roots exposed and it dries out. Water in well and keep the bed moist for a fortnight.

Mulch under the developing fruit with straw or a woven mat in late May. This keeps berries off wet compost, cuts slug damage and reduces the splashing that spreads mould. Remove runners as they appear unless you want new plants; a runner takes energy that would otherwise go into fruit. Water at the base in the morning where you can, and use rainwater if your tap supply is hard. Top up with ericaceous compost each autumn and plan to replant the bed every three years, when virus and crown rot begin to bite.