Express-News Weekly Column
Saturday, December 7, 2002
Submitted by Calvin Finch, Ph.D., Manager, Conservation Division, Water Resources & Conservation Department, SAWS, and Horticulturist

            Do you want to successfully grow vegetables or flowers in the San Antonio area? If so, a raised bed is the way to garden. Building a raised bed is relatively easy.

            Locate a level place in full sun. A shady location is okay for some flowers and foliage plants, but for vegetables and most flowers, full sun is necessary. Some folks do all kinds of elaborate things to the soil surface before they build; I don’t think it is necessary. Putting plastic over the native soil to keep Bermuda grass from invading the raised bed slows the weeds down but also eliminates the native soil as a reservoir for plants with relatively deep roots like tomatoes. Another strategy is to spray the area with Round-up. Round-up kills the Bermuda grass if it is sprayed in early fall or late spring. Now is too late because the cool weather ends the active growth of the Bermuda grass.

            Newspaper spread over the ground is fine. It will decompose about the time the Bermuda grass begins to grow again. In my raised bed gardens I control Bermuda grass by hand and by spraying with a grass herbicide like Vantage or Poast in between crops. It also helps to spray a killed area around the raised bed.

            There are many materials that work well for the garden walls. Used railroad ties are my favorite. Ties laid end to end are heavy enough to stay put and deep enough to grow roses, tomatoes, and all annuals. CCA treated timbers also are very easy to use. Arranged like Lincoln Logs three timbers tall with the overlap ends nailed together; they are light and work for years.  CCA timbers will be off the market soon because of the fear of the arsenic used as part of the treatment process. In several years of tests, the level of arsenic in the raised beds in San Antonio and other areas never reached levels higher than the levels expected in the native soils. Arsenic is a component of all soils and living organisms. It becomes a poison only at relatively high levels, but the material is scary and the industry will seek alternate treatment chemicals.

            Cement blocks, rock, plastic wood, and cedar can also be used for raised beds.

            The soil you use to fill your raised bed is very important. A mix of one-third sand, one-third compost, and one-third native soil is recommended. The landscape mixes offered by Fertile Garden Supply, Keller Material, Garden-Ville, and other suppliers work well. It takes about one cubic-yard of landscape mix to fill an 8 by 8 foot raised bed. The material is about $20 if you pick it up yourself; add $35—$50 for delivery.

            Compost decomposes and compacts in the bed, so expect to replenish the bed every two years with new compost.

            If you build your bed 8 feet wide and multiples of 8 feet long, the ties or timbers do not have to be cut. However, a 4-foot wide bed is the easiest to garden. The middle can be reached for weeding or planting from either side without treading on the soil.

            To really make your raised bed productive, construct a drip irrigation system. For many years my vegetable garden drip system was a simple kit obtained from the home improvement store fed by a hose run on the surface of the lawn. It worked great. Your favorite nursery has the drip kits and so do the soil suppliers. Soaker hoses also work. Remember, for soaker hoses to be effective as a drip irrigation, barely turn the water on. The water should flow from the hose very slowly to be effective.

            Build the bed, construct the drip irrigation system, collect your leaves to use as mulch, and you are in business to grow a great vegetable garden, beautiful annual flowers and high quality roses.