Raised Bed Vegetable Gardening

Gardening in raised beds, a common practice before colonial times, is enjoying a  resurgence of popularity among home vegetable growers. In regions of the world with greater population densities or less tillable land, gardening in beds is still the norm.

"Raised" means that the soil level in the bed is higher than the surrounding soil, and "bed" implies a size small enough to work without actually stepping onto the planting area. A bed should be no wider than 4 feet but length can be whatever suits the site or gardener's needs. Wider beds can be subdivided into sections accessible from planks or stepping stones. The bed does not have to be enclosed or framed. The use of power tillers is feasible, for example, in unframed beds, although a properly maintained bed should not need power-cultivation.

Advantages

There are many reasons for choosing raised bed gardening, including higher yields, improved soil conditions, ease of working, ease of pest control, and water conservation.

Higher Yields: Raised beds result in more production per square foot of garden. In a traditional home garden good management may yield about 0.6 pound of vegetables per square foot; studies of raised bed production over a three year period show an average of 1.24 pounds per square foot, more than double the conventional yield. Raised beds do not require the usual space between rows since no walking is done in the bed to cultivate or harvest. Hence, vegetables are planted in beds at higher densities – ideally spaced just far enough apart to avoid crowding but close enough to shade weeds.

Improved Soil Conditions: Soil compaction can reduce crop yields up to 50 percent; water, air, and roots all have difficulty moving through soil compressed by tractors, tillers, or human traffic. Plows, tillers, or spades have been the usual answer to this problem but gardeners can avoid the problem completely by creating beds narrow enough to work from the sides. Content of soil organic matter can be increased greatly without getting bogged down. Raised beds also help in problem soil situations where compaction is not the only culprit. The landscape may have low spots unsuited for conventional gardens because of ponding or excessive erosion from runoff. Raised beds rise above these problems with frames as a foundation. Soil acidity can thus be more easily maintained in the 5.8 to 6.8 pH range, which is preferable for most vegetable culture.

Ease of Working: The first, and most important, benefit of gardening with raised beds is the increased ease of timely planting and harvesting. Many people avoid working traditional gardens in rainy weather to avoid compaction and muddy feet. Because raised beds are designed for walking around, not in, there is no reason for mud to delay operation. Spaces between beds may be mulched or even paved with stone or brick.

Ease of Pest Control: Pest control is easier in raised beds. If burrowing rodents are abundant the bottom of the bed can be lined with poultry wire or hardware cloth. Rabbits and groundhogs can be discouraged simply by placing their favorite foods in a framed bed with a low fence. The narrow dimensions of beds even make bird netting suspended on flexible conduit frames practical. Weed control with plastic mulch can be achieved economically as the width of the bed can be spanned by one roll.

Water Conservation: The narrow dimensions of raised beds are advantageous for water conservation. Canvas soaker hoses, perforated plastic sprinkle hoses, and drip-type irrigation disperse water in a long, narrow pattern. Directing water to the soil helps to reduce disease problems which can result from wetting the foliage with overhead sprinklers.

Construction Tips

There are only a few guidelines to remember in raised bed construction:

1. Keep the beds narrow and match their length to the site and the watering system. A north-south orientation is best for low-growing crops, allowing direct sunlight to both sides of the bed. Beds that will contain taller crops such as pole beans, trellised peas or caged tomatoes might do better on an eastwest axis – lower-growing crops could be planted on the south side of the bed and still get full sun.

2. Avoid the use of creosote- or pentachlorophenol-treated lumber for bed frames as these chemicals can leach out and injure plants. Use pressure-treated lumber, redwood, cement block, or brick; be aware that the cement in block will raise soil pH over time. Framing materials can also be large stones, untreated lumber, sapling trees, straight logs, or recycled plastic lumber. Obviously, colonial farmers did not have all these materials available. You could just hill up the bed and maintain it regularly.

At least one-third of the volume of the bed's root zone should consist of existing soil. Add one-third compost or peat and one-third coarse sand to create a well drained soil. Add a little garden fertilizer and test the soil after the first crop year.

Raised bed possibilities are endless. Beds elevated 2 feet or more offer the promise of gardening without bending and can have benches built on the sides for even more convenience. Because a bed warms up quicker than the ground, it can easily double as a cold frame by covering it with a lightweight clear plastic cover. Imagine being able to start plants early in beds with covers and never having to transplant them! Supports for poles, cages and trellises can be mounted to the frame for longer life and ease of installation and removal.

Adapted from Pete Lane, Ohio State University Extension, 2000