Raised Bed

A raised bed is a growing area held above the surrounding ground and filled with soil brought in rather than the soil already there. Four rather different reasons sit under one shape. It lets a crop grow where the ground cannot be used at all: contaminated, compacted, paved over, or off limits. It brings the work up to a comfortable level, around 70 cm (27 in) for a gardener in a wheelchair. It warms faster in spring than the ground beneath - the point of it where spring is slow to warm, a drawback where heat is the problem. And perennial weeds, which return from their roots each year, trouble it less.

Reach sets the width: the test is working the middle without stepping in. A bed reached from one side stops near 75 cm (2.5 ft), one reached from both near 1.5 m (5 ft), and a ground-level bed is usually 15 to 20 cm (6 to 8 in) high. Boards longer than about 1.8 m (6 ft) warp and break. The fill is roughly half to two-thirds topsoil and the rest plant-based compost; heavier on compost and the mix dries out fast and can then shed water rather than soak it up. Height and thirst move together: a bed dries faster than open ground, and the taller it is the more often it needs watering.

What the sides are made of sets how long the bed lasts. Cedar and hemlock far outlast pine or fir; old or arsenic-treated timber is avoided in favour of copper-treated boards rated for ground contact; galvanised steel resists rust for decades but its zinc leaches where soil is strongly acid. One mistake cannot be fixed later: wire mesh must go under the fill at build time or rodents tunnel up from beneath. The fill is a closed volume and drifts, so test it every two or three years; heavy yearly compost builds up phosphorus. Keeping a crop family out of the same bed for three or four years is easier with several small beds than one large, a layout decision made before anything is built.