As planting season is here, in this column we are providing information about raised-bed gardening.
Raised-bed gardening is a popular technique for growing plants in Missouri. Vegetables, fruits, flowers, trees and shrubs may be grown in raised beds, which can be attractive as well as useful.
Advantages of raised-bed gardening
Raised-bed gardening has many advantages. Growing plants in raised beds is a logical choice for gardeners with heavy, poorly drained soils. Raised beds permit plant roots to develop in soil held above water-logged for compacted zones. This soil environment is much better for root growth. As beds are built up, compost or other forms of organic matter may be incorporated, further improving soil structure, drainage and nutrient holding capacity.
Better root growth from improved soils leads to higher yields for food crops and lusher growth of ornamental plantings. Also, intensive planting in raised beds means more plants can be grown in a smaller area than with conventional row-cropping techniques. No space is wasted between rows.
Better drainage speeds soil warming and allows earlier spring planting. In wet seasons, soil dries faster, so planting can proceed between rains.
Because plants grow above the level of walkways, less stooping is required for weeding, watering and other chores. Intensively planted raised beds provide dense foliage cover, shading out much weed growth.
Raised beds make gardening possible on sites where growing plants would otherwise be possible. Rooftop gardens and raised beds on top of solid rock are examples. Terraced raised beds turn hillsides into productive growing areas while reducing soil erosion potential.
Types of raised beds
Temporary raised beds work well for many backyard vegetable gardeners. As the soil is tilled, it is loosened. If tillage equipment and foot traffic are kept off tilled beds, the loosened soil remains slightly raised above surrounding pathways. Adding compost or other organic matter to the bed raises it even higher.
The main advantage of temporary raised beds is their simplicity. No expense is involved in constructing framework to contain the soil. Temporary beds are less labor intensive to make than permanent beds. However, temporary beds flatten over the course of a growing season and require reconstruction the next year.
Permanent raised beds are more satisfactory for most situations. In the landscape, planting berms may be constructed by harling in topsoil to create traffic barriers as well as visual interest. When planted and mulched, berms need no edging to keep the soil in place. Walled raised beds may be used in the landscape for vegetable gardens. Besides controlling erosion better than temporary beds, walled beds permit deep soil amendment.
Although constructing walls for raised beds takes labor and has an initial cost, the finished product should last for many years.
Soil mix
Good quality existing topsoil may be used in raised beds. However, the addition of organic matter to any soil will improve its physical and chemical makeup, thus making it more productive. Peat moss, compost and decomposed manures are good sources of organic matter.
To take full advantage of the deep rooting potential with raised beds, work up the base soil by rototilling or hand digging before bringing in additional soil. Many gardeners double dig beds.
Double digging involves removing the topsoil the depth of a spade, setting the soil aside, then loosening the subsoil another spade's depth. Finally, the topsoil is returned with added amendments, such as compost, manure or fertilizers. This labor-intensive soil preparation method provides an excellent rooting zone for plants. However, less intensive methos also permit satisfactory plant growth.
Maintenance of raised beds
Soil in raised beds warms faster and dries out more quickly than soil at ground level. In spring and fall, these traits are desirable. They are less desirable during the heat of summer.
Use of organic mulches, such as straw or hay, in vegetable gardens, or wood chips placed on landscape fabric weed barriers around ornamental plantings help combat both problems. Soil temperatures are lower under organic mulches, less water is lost through evaporation, and weed growth is suppressed. Use irrigation to supplement natural rainfall during dry periods. Soaker hoses or drip irrigation may be placed directly on the bed. Overhead sprinklers can also be used, but because they wet foliage, they are more likely to spread diseases.
At the end of the growing season, plant residue in a vegetable garden can be tilled into the soil, adding organic matter. Additional compost may be added before the next planting. Over time, the soil may become improved enough so little additional tillage will be necessary.
Fertilization of plant grown in raised beds is similar to that of plants grown conventionally. For most crops, a complete fertilizer such as 10-10-10 applied at the rate of 1 to 2 pounds per 100 square feet is satisfactory. Organic fertilizers and manures may also be used. For specific fertilizer suggestion rely on recommendations based on soil tests.
Source: MU Extension guide sheet g6985.
Dhruba Dhakal, PhD, is a University of Missouri Extension Horticulturist, serving to Missourians for about a decade in Central Missouri. Dhakal can be contacted at [email protected] with gardening questions.