Blackwelder column: Raised garden beds

Published 12:00 am Friday, January 21, 2011

Raised bed gardening is becoming a very popular gardening method, especially for those with limited space or mobility.
With the continued economic stress, many people are also starting a vegetable garden to save money. Using raised beds was a common cultural practice in colonial gardens.
This style of gardening has a number of advantages, especially for the beginner gardener. One of the greatest advantages is increased yields over conventional gardens. Studies in Ohio indicated that a traditional home garden with good management yielded a little over a half a pound of vegetables per square foot.
In a three-year study of raised bed gardens, researchers produced an average of 1.24 pounds per square foot, more than double that of a conventional garden. Generally, most vegetable crops can be planted more densely in raised beds.
An obvious advantage is soils in raised beds can be amended to reduce soil compaction, allowing for greater root growth, expansion and ultimately, healthier plants. Heavy tillers and plows are not needed for raised vegetable gardens. Organic matter content is easily incorporated with small tillers and hand tools. Organic matter greatly increases productivity as well as pore space and nutrition for maximum plant growth.
Raised beds warm up quicker in the spring and fall than conventional gardens. The growing season for early spring crops as well as fall crops can be extended with raised beds.
Another asset of raised beds is gravity. Raising the growing media allows soggy soils to rapidly drain for ease of maintenance and harvest. Conversely, these beds also aid in water conservation. Strategically placing soaker or drip hoses directs water directly to the root zone instead of wetting leaf surfaces with overhead irrigation, reducing foliar diseases.
Below are a few guidelines to consider in raised bed construction:
• Keep the beds narrow and match their length to the site and the watering system. Bed dimensions of 4 by 10 feet are considered a standard and work well for most vegetable garden applications.
• The height of the raised bed should be a minimum of 10-12 inches. Beds elevated 2 feet or more offer promise for those with physical impairments. Benches can be built on the sides for even more convenience to those with limited mobility.
• Locate the raised beds in full sun. Shady or even partial shade locations often yield poor results.
• Water is important for all vegetable gardens, both conventional and raised bed gardens. Raised beds tend to dry out quickly, especially in hot weather. Have a reliable water source nearby.
• Avoid using creosote or pentachlorophenol-treated lumber for bed frames. The wood preserving chemicals often leach out and injure plants. Use pressure-treated lumber, cement block or brick. Those that have an aversion to any type of treated lumber can line the inside with plastic. Please note that over time, cement used in the block will raise soil pH.
• Even with heavy clay soil, it’s best to have at least one-third of the volume of the bed’s root zone growing in native soil. Clay soils contain a plethora of nutrients. Incorporating ground pine bark, compost and PermaTill (soil amendment) provides an optimum growing medium for most vegetables. Test your soil medium and follow N.C. Department of Agriculture fertilization recommendations.
Darrell Blackwelder is the County Extension Director with horticulture responsibilities with the North Carolina Cooperative Extension Service in Rowan County. Learn more about Cooperative Extension events and activities on Facebook or website at