Building a raised bed — easy on the back, early to start, high-yielding

A Raised bed is essentially a hügelkultur in a box — the same layered decomposition, just packed into a back-friendly frame. You work standing up, the bed warms up earlier in spring, and the lower wood layer feeds your plants for years without you topping up the fertiliser.

Why a raised bed?

• Easy on the back — 31.5 in tall, no bending.
• Earlier start — the rot inside generates heat, the soil is 1–2 weeks ahead.
• Better Drainage — the coarse base prevents Waterlogging.
• Fewer Slugs — the edge is a real hurdle, especially with a slug barrier strip.
• High yields — loose, warm, nutrient-rich soil in the first year.

Material & dimensions

A width of no more than 47.2 in–51.2 in is proven — that way you can reach the middle from both sides without stepping in. The length is free (in the Garden Planner 19.7 × 2.6 ft is the default). Height 31.5 in for comfortable working.

• Frame: untreated larch or Douglas fir (lasts ~10 years without impregnation), alternatively stone, gabions or black locust. No pressure-treated wood next to vegetable beds.
• Inner side: line it with dimpled membrane or pond liner — it protects the wood from the permanently damp fill and extends its lifespan considerably.
• Base: a galvanised vole mesh (fine-meshed) under the bottom layer — otherwise voles will be delighted by the roots.

The fill — coarse to fine

The principle is the same as with compost and with the hügelkultur: coarse, carbon-rich material at the bottom that decomposes slowly and gives off heat; fine planting soil on top. From bottom to top:

1. Coarse wood & branches (7.9 in–11.8 in): tree and shrub prunings, thin trunks. Stores water, provides air.
2. Inverted turf / shrub prunings (5.9 in): grass side down. Decomposes and closes the gaps.
3. Leaves & green cuttings (5.9 in): autumn leaves, shredded plant remains, a little straw.
4. Half-mature Compost (5.9 in): brings in the microorganisms and starts the rot.
5. Planting soil / mature compost (9.8 in–11.8 in): the actual root zone — good garden soil mixed with mature compost.

Lightly firm and water each layer — this prevents large air pockets that later cause settling. Reckon on about 7.9 in of sinking in the first year; top up with compost and soil every spring.

The first year: mind the nitrogen lock

Fresh wood inside binds nitrogen at first (it "pulls" it out of the soil in order to decompose). In the first year the raised bed is therefore nutrient-rich, but at times nitrogen-poor at the boundary layer. In the first year you're better off going with:

• Fruiting vegetables that get fed anyway: tomato, cucumber, courgette (they benefit from the heat of the rot)
• Nitrogen fixer such as beans and peas, which supply nitrogen themselves
• Lettuce and herbs

From year 2–3 the bed is at its peak — anything goes. After 5–7 years the fill has largely decomposed into humus and sinks heavily; then you empty the bed (the contents are the best compost for your garden bed) and refill.

Care

• Water regularly in the first summer — the wood has to soak itself full first.
• Mulching with straw or shreddings holds the moisture and saves water.
• In autumn sow a green manure so the soil stays covered and alive over winter.
• Every spring top up with 2.0 in–3.9 in of mature compost — this offsets the settling.

In the Garden Planner raised beds are intended as kitchen-near herb and lettuce beds in zone 1 — 19.7 × 2.6 ft as the default size, freely adjustable in the detail planner.