Raised beds are elevated garden plots created by mounding soil above the surrounding ground level, typically within a framed enclosure. They provide improved Drainage, warmer soil in spring, better root aeration, and reduced soil compaction compared to ground-level gardening. Raised beds allow gardeners to create optimal Soil Composition independent of the native soil quality. Standard raised beds are 15 to 30 centimeters (6 to 12 inches) tall and 0.9 to 1.2 meters (3 to 4 feet) wide to allow easy reach from both sides.
Ungrounded raised beds sit directly on the soil surface and allow roots to penetrate into the native subsoil below. These are the most common type and are suitable for most vegetables and annual crops. Bottomless beds are similar but have a solid frame that extends above and below ground. Fully contained beds have a solid bottom and are used on patios, balconies, or areas with contaminated soil where separation from ground soil is necessary. In greenhouses, raised benches are a form of elevated bed that brings plants to working height.
Framing materials include untreated lumber, cedar, redwood, recycled plastic lumber, concrete blocks, stone, and corrugated steel. Cedar and redwood naturally resist decay and can last 10 to 15 years. Pine treated with ACQ (alkaline copper quaternary) is a modern alternative to older CCA-treated wood and is considered safe for vegetable gardens. The bed is filled with a mixture of topsoil, compost, and other amendments, typically in a ratio of 60 percent topsoil to 40 percent organic matter.
Raised beds are especially beneficial in areas with poor native soil, heavy clay, or drainage problems. They warm faster in spring, allowing earlier planting of warm-season crops. The loose, well-aerated soil reduces root friction and supports vigorous root growth. Raised beds facilitate intensive planting methods such as square-foot gardening and produce higher yields per unit area than traditional row gardening.