For superior home-grown veg simple wooden raised beds are well worth considering.
They’re good for drainage and easier to access for those with mobility concerns. Importantly, raised beds minimise problems associated with soil compaction as you needn’t walk over the soil. Plus, filled with fresh compost it’s possible to grow tasty crops with success, no matter how poor the soil is underneath.
Pick a level weed free spot. Persistent perennials like bindweed need to be carefully removed. Rather than using a translocated weed killer, consider digging out the roots with a fork, unless it’s a large problem.
Old scaffold boards or similar, are perfect for the frame. If the timber isn’t tantalised or treated, coat it with eco-friendly preservative so it lasts. One 225mm board on edge is deep enough for most vegetables. If the plan is to position raised beds on concrete or old paving, you’ll need to add another board on top of the first for a deeper bed for the concrete underneath will obviously impede the roots of permanent plantings and root crops like carrots and potatoes.
Mark out the bed on the ground to check it fits comfortably in the space. Unless you can access it from both sides, aim for a width no more than 1.2-1.5m or you’ll struggle to reach across without stepping on the bed, and in turn compacting the soil.
- Cut the timber to size and fix the corners together using 3×3” treated fence posts, cut slightly shorter than the height of the sides.
- Use long deck screws, or similar. Fire in three or four per end.
- Check the frame is square as you go using a carpentry or rafters square in each corner, or continually check that the diagonal measurement from one corner to the opposite one is the same. Now nestle the frame into position.
- To stop the sides bowing out use treated 2×2” wooden battens or ¾” steel rebar (from builders’ merchants) cut to size and hammered in on the outside every 40-50cm or so.
To elevate the status of colourful ornamentals or for a permanent bed for veg use railway sleepers (try local builders merchants, or online retailers if it’s not possible to pick them up locally). New softwood sleepers are relatively inexpensive, easy to cut and light. Oak costs more but weathers beautifully. Never use reclaimed railway sleepers; they’re impregnated with foul preservatives and tar.
- For sleeper beds, mark out the position of the bed and compact the soil where they’re going to go with the head of a sledgehammer. Use a thin layer of sharp sand to help get a level base – use a sprit level to check. Then place the sleepers in position. Secure them using thin wooden pegs or short lengths of rebar hammered in either side (be sure to watch for sharp edges). For a tidier finish fix heavy duty angle brackets (ideally galvanised) inside to hold the corners together.
- For a deeper bed stack another layer on top of the first. Alternate the corners and stagger the joints. Screw them together using long coach screws or Timberlock screws of an appropriate size – they are expensive but need no predrilling. If you have a plug cutter, make plugs from an offcut of the same timber and use these to hide the screw holes on the top.
- Once the frame is finished, deeply dig over the bottom of the bed. Skim off any grass (if it’s not been removed already) and stack it near the compost heap grass-sides facing until it rots down into compost.
- Fill the bed with soil. Use spent compost from old baskets and pots, the contents of the compost heap, cheap peat free grow bags, soil-based compost or soil conditioner from DIY stores. For deep beds you might need to buy in ton bags of screened topsoil (try www.rolawndirect.co.uk, price depends on quantity and location). A 1m3 bag covers up to 5m2 at a depth of 20cm. Be mindful if you mix in soil skimmed from borders around the garden; if it’s scraped from the surface in particular it may be full of weed seeds. Put this at the bottom, with clean compost on top to minimise potential problems.
Note: Raised beds on concrete or paving need a thick 8-10cm layer of drainage material in the base so that the compost doesn’t become sodden (20-30mm gravel, or lots of broken terracotta crocks is ideal). Using a ¾” spade bit drill a few drainage holes in the sides close to the bottom of the frame too. The deeper the bed the more soil and compost is obviously required. In this context it might be better growing deep rooted veg in old co-extruded (black on the inside, white on the outside) compost sacks or galvanised metal dustbins instead.