Why Cedar Offcuts Are Worth Hoarding

If you have had a cedar garden room or shepherd hut built recently, the chances are you are still tripping over a stack of offcuts at the side of the shed. Western red cedar is far too good to burn. It is naturally durable, dimensionally stable and rich in oils that shrug off damp, which makes it one of the finest timbers for anything that sits outside in British weather. A raised planter is the obvious project: it needs only short lengths, tolerates slight differences in thickness and gives you something useful within an afternoon.

The plan I set out below makes a 600mm square planter roughly 400mm tall, using 20mm cladding offcuts for the sides and 45mm square lengths for the corner posts. Scale it up or down as your stock allows, but keep the proportions roughly the same so it does not look top-heavy.

Sorting and Preparing Your Timber

Before you cut anything, spread the offcuts out and sort them into three piles: lengths over 600mm, lengths between 300mm and 600mm, and short pieces. Set aside anything with old nails, staples or heavy splitting. Knots are fine, provided they are not sitting right on a cut end where they will weaken the joint.

• Brush off sawdust and site grime with a stiff brush so your pencil marks and glue take properly.
• Run a plane or an orbital sander over the sawn edges; cedar fuzzes easily and a light pass makes a surprising difference to the finished look.
• Check each piece for twist by laying it on a flat surface. Twisted boards will fight you when you come to assemble the frame, so reserve them for the slats rather than the posts.
• Mark out your cutting list with a pencil and a square, working from your longest piece first so a mistake costs you the least timber.

Cutting the Parts

For a 600mm square planter with corner posts, cut four posts at 400mm from your 45mm stock. Then cut side slats: 520mm for the two side runs that sit between the posts, and 600mm for the front and back runs that cover them. If your offcuts are all cladding, work instead with a simple butt-jointed box and add four internal corner battens to give the screws something to bite into.

Cedar splits readily near an edge, so always pre-drill. Use a bit roughly 1mm smaller than the shank of your screw. Stainless steel screws are worth the extra few pounds here — plain steel will stain the timber black within a season as it reacts with the natural tannins in the wood. I would use 4 x 40mm screws for slats and 5 x 70mm for fixing into posts.

Assembling the Frame

Work on a flat surface, ideally a pair of trestles with a sheet of ply across them. Lay out the four posts and fix the bottom slat of each side first, sitting it just above the base of the posts so the timber is clear of the ground. Check the diagonal measurements across the corners as you go — if they match, the box is square.

• Space the slats 8–10mm apart. The gap lets air move through and stops damp gathering between boards.
• Fix each slat with two screws per end, staggered slightly so they do not split along the same grain line.
• Work your way up one side at a time, checking for square again once you reach the top course.
• Finish with a capping rail around the top edge if you have a longer piece spare — it tidies the rim and gives you something to rest a trowel on.

Lining, Drainage and Filling

A planter built from cedar will last many years untreated, but lining the inside buys you another decade. Staple a butyl or EPDM liner to the inner faces, leaving the base open. If your planter sits on paving, cut a base panel from offcuts, drill a grid of 10mm drainage holes in it, and rest the whole thing on four short battens so air can move underneath. That single detail does more for longevity than any surface treatment.

Add 50mm of gravel over the base, then a layer of geotextile to stop the compost silting into it. Fill with a loam-based compost blended with about a quarter by volume of horticultural grit, which suits the Mediterranean and cottage favourites that look best in cedar.

Finishing and Planting Up

Left alone, cedar weathers to a soft silver-grey that sits beautifully against brick, stone or a painted shepherd hut. If you prefer to keep the warm reddish tone, brush on a breathable oil rather than a film-forming varnish, which will trap moisture and peel. Re-oil every couple of years, ideally in early autumn.

For a cottage feel, plant thyme, lavender, rosemary or alpines in a sunny spot, or ferns and hellebores where the planter sits in shade. Leave a little space between plants at the outset — a cedar planter this size fills out faster than you expect, and you will be glad of the room come July.