Raised Beds

Raised beds provide an optimum environment for germination and growth, especially when used with the stale seedbed technique. Raised beds are formed with special bed shapers. Raised beds improve drainage and hasten the drying of soil. Without irrigation, bed height should be restricted to 4". When irrigation is available, bed height can be raised to increase air flow and benefit crops such as lettuce. In areas of heavy rainfall, crops are seeded on beds so that excess water drains off. Yields of vegetables such as carrots and parsnips, where root length is important, are often increased because the depth of friable soil is greater. Pre-formed raised beds warm up faster and allow for early seeding. Raised beds can also reduce the incidence of Phytophthora root rot, damping-off, and feeding by slugs because raised beds can dry out more quickly than flat beds. Herbicides are often incorporated into the soil at the same time or just after the beds are made. Be certain that the herbicide is incorporated to the proper depth. For best results, do not incorporate the herbicide before the beds are made; the herbicide will likely end up too deep and cause crop injury; or concentration can be increased when soil is piled up while forming the beds.

Wind damage is reduced with raised beds. Level soil has a more pronounced airfoil effect, and with the wind passing over them, this allows for a partial vacuum effect. Soil particles are more easily lifted and seedlings more often twisted. The resulting abrasions on the plant surfaces allow for easier disease introduction if conditions are favorable to the pathogens. Raised beds break up the airfoil effect, reduce the twisting of seedlings and the number of airborne soil particles. Wheel traffic is also restricted to a narrow zone between the beds.

Growers should consider bed direction and the slope of the bed. During cool, spring days, maximum warming of the bed is needed to provide suitable conditions for plant growth. When the days are short and temperatures are low, orient the beds north and south if two rows per bed are used (if soil erosion is not a consideration). If beds are set in an east-west orientation, the rows planted on the south side of the bed get more heat and grow faster than rows planted on the north side of the bed. This can lead to a lack of uniformity at harvest time. However, beds that are oriented across the slope following the contour of the land minimize soil erosion. For instance, on south-facing slopes, beds of spring crops should be oriented east-west.