Building, filling and planting a raised bed

A raised bed is more than a bed on stilts. The layered structure sets off a decomposition process inside that supplies warmth and nutrients over months. The result: an earlier start in spring, stronger growth, and a harvest that in the first year clearly beats ground level.

On top comes the practical advantage you only appreciate once you have it: you work standing up, slugs have a harder time, and the soil is never compacted because nobody treads on it.

In short

Ideal height for working standing up: 80 to 90 cm, width no more than 130 cm.
The layering from coarse to fine is the heart of it — do not simply fill it with soil.
Hungry crops in the first year, then moderate and finally light feeders.
The filling sinks 10 to 20 cm a year: top up with compost each spring.
After four to six years the filling is spent and gets replaced.

Position and dimensions

Sun: at least six hours. Orient the long side north to south so all plants get even light.
Width no more than 130 cm if the bed is reachable from both sides — otherwise 70 cm. You must be able to reach the middle comfortably.
Height 80 to 90 cm for working standing; 60 cm for sitting height.
Base: directly on natural soil is best, then earthworms can move in. On a sealed surface you need a closed floor with drainage holes.
Vole mesh in the base if the bed stands on soil. Galvanised mesh with 13 mm aperture, pulled up at the edges.
Line the inner walls with dimpled membrane — it protects the timber from permanent damp. Do not seal the base.

The layers from bottom to top

The layering is not a ritual but physics and biology: coarse material at the bottom provides air and drainage, fine material at the top serves the roots. In between, the decomposition runs that supplies warmth and nutrients.

1. Coarse prunings (20 to 30 cm): branches, twigs, tree cuttings, root pieces. This is the air cushion and the drainage.
2. Upturned turf or leaves (10 to 15 cm): stops the finer layers trickling straight down.
3. Rough compost, shrub prunings, chippings (20 cm): this is where decomposition runs hardest.
4. Half-ripe compost or manure (15 to 20 cm): the nutrient reserve.
5. Ripe compost and garden soil (20 to 30 cm): the actual planting layer. Good, finely crumbly soil belongs here — do not economise on this layer.

Tread each layer down and water it well. A dry raised bed does not start to decompose. It is best filled in autumn — by spring the filling has settled and is already working.

What grows in which year?

In the first year decomposition releases a great deal of nitrogen, more than most crops can handle. Hence the classic schedule:

Year 1 — hungry feeders: tomato, cucumber, courgette, squash, cabbage, celeriac, leek. They take up the nitrogen.
Year 2 — hungry and strong moderate feeders: additionally pepper, aubergine, chard, beetroot.
Year 3 — moderate feeders: carrot, onion, lettuce, fennel, kohlrabi, spinach.
Years 4 and 5 — light feeders: radish, lamb’s lettuce, beans, peas, herbs.
After that: replace the filling. The contents make excellent compost for beds in the garden.

Caution

Leaf crops such as spinach, lettuce and chard accumulate nitrate in the first year when too much nitrogen is available. Grow them in a raised bed only from the third year — or as a late-summer follow-on crop, once the nitrogen surge is over.

Care through the year

Watering: raised beds dry out faster than ground beds because they catch wind and warmth from all sides. Check daily in summer.
Mulching cuts evaporation markedly and is particularly effective in a raised bed.
Topping up: every spring the filling sinks 10 to 20 cm. Top up with ripe compost and garden soil.
Feeding: from year three help along with organic fertiliser; before that there is enough in the system.
Winter: do not leave the bed bare. Green manure or a mulch blanket protects the top layer from leaching.

Tip

A cold-frame top or a simple hoop with fleece extends the season by three to four weeks at each end. Combined with the warmth from decomposition, you can often set the first lettuce in a raised bed as early as late February.

Common mistakes

Filled with soil only. Without coarse layers everything collapses, holds water and delivers no warmth.
Built too wide. Anyone who cannot reach the middle eventually climbs in — and compacts precisely what should stay loose.
Thuja clippings or walnut leaves built in. Both inhibit growth. Use fruit and deciduous tree prunings instead.
Too little planting layer. Under 20 cm of fine soil, carrots and cabbage do not root properly.
Bark mulch as filling. It takes nitrogen out of the soil as it rots instead of supplying any.

Frequently asked questions

Which material suits the frame?

Larch and Douglas fir last 10 to 15 years untreated, spruce only 5 to 8. Metal and stone last longer but heat up more. No pressure-treated timber for vegetables.

Can I plant it up in the first year?

Yes, if you filled it in autumn. When filling in spring, wait a few weeks and choose vigorous crops — decomposition is still very active then.

Do I have to seal the inside completely?

No, only the side walls to protect the timber. The base must stay open, otherwise water builds up and soil organisms cannot get in.

How much filling material do I need?

A bed of 2 by 1 m at 80 cm height holds around 1.6 cubic metres. About half of that is coarse material from your own garden, the rest compost and soil.

Because a freshly filled raised bed really gets going in the first year, sturdy young plants pay off especially well here — they use the nutrient surge immediately instead of letting it go to waste.