Consider a raised bed if you live in an area where the soil is rocky or mostly sand or mostly clay. Adding organic matter to your soil is always a good idea and will always help make poor soil better. But sometimes a raised bed is the best solution.
You can choose the soil in your raised bed. You can purchase rich garden soil at the garden center or you can make your own by taking native soil from nearby and amending it with well-rotted manure and compost until it is rich and loamy.
The soil in a raised bed warms more quickly in spring—that’s good in short season and cool coastal regions. A raised bed also can be made tall enough to aid a back tired after years of bending. And the width of a raised bed will allow you to work your vegetable bed from different sides.
A bed width of no more than 4 feet (1.2 m) will allow easy access from each side. You don’t have to worry about soil compaction with a raised bed. All of your gardening is done from the edge. You can bring a chair, stool, or wheelchair to the edge of a raised bed. The more narrow the bed, the easier it is to reach into the bed without having to lean on the soil.
A raised bed can be as little as 8 inches (20 cm) deep for shallow rooted vegetables such as lettuce, spinach, and Asian greens. A raised bed 12 inches (30 cm) deep will work for root vegetables such as beets, carrots, and turnips and larger vegetables with deeper roots such as cabbage and Brussels sprouts. A bed 20 inches (50 cm) deep is best for fruiting vegetables such as tomatoes, eggplant, and beans. The roots of rooting vegetable reach deepest into the soil.
You can make a raised bed by simply placing a bottomless container or box in your garden and filling it with soil. You can also build a raised bed with lumber that has not been chemically treated, or you can place rocks in a square or rectangle and fill the area with good soil. You also simply mound the soil in your garden to create a raised planting area.
To edge a raised bed with wood, choose 2 by 6 or 2 by 8-inch lumber. Use two or three levels of boards held in place by stakes. Leave paths of 2-3 feet (60-90 cm) wide between the beds. Place newspaper covered by sand or shredded bark in the pathways to keep the weeds down.
With a raised bed you can concentrate your watering and plant care on the exact ground that will bring your food to the table. Raised beds cut down on soil compaction which can affect plant growth and productivity.
Not all vegetables are suited for raised bed gardening. Tall crops such as corn and sunchokes might be more easily managed in a level garden. But tall and vining crops can be grown in a raised bed where the trellis is placed on the north side of the bed allowing the tall crops to grow without shading the shorter crops.