USING RAISED BED GARDENS

            If you are new to the South Texas area or have recently decided you want to get serious about gardening, raised beds are the most practical way to grow vegetables, annual flowers, modern roses or fruit trees. We use raised beds because the native soil is rocky, poorly drained or absent. Many area residents have rock where soil is normally found.

            Raised beds have been described as containers on a large scale. In most cases, however, they are containers without bottoms. Raised beds have several advantages over native soil: you can have “perfect soil”, they warm up fast in the spring, and they drain very well. Garden them intensely by planting rows close together, fertilizing frequently, using drip irrigation, gardening 12 months out of the year, and you will have large yields per square foot of garden.

            Some type of material needs to be selected for containment of the soil. Among the choices are rock, cement blocks, cedar lumber, treated lumber, landscape timbers, used railroad ties, and plastic lumber. I like used railroad ties or treated wood the best but have used rock, cement blocks, plastic lumber and landscape timbers as well. Treated lumber and landscape timbers scare some people because they are treated with CCA (chromium, copper, and arsenic), but field research I have done indicates they are safe. Locally conducted soil tests also verify the safety of used railroad ties.

            Select a level, sunny spot for your raised bed. If you have any native soil at all you can produce good flowers and vegetables with a bed 8 to 12 inches deep (one railroad tie, three landscape timbers, one cement block, etc.). There are several options with the native soil under the raised bed. Some gardeners kill all the grasses with Round-up, double dig or till it, and others cover it with plastic or newspapers. I don’t do anything to it.

            Covering the ground with plastic reduces drainage from the raised bed and prevents your tomatoes, roses or peach trees from utilizing the soil that is available. The newspapers and Round-up slow down weed encroachment but, eventually, some weeds will find their way into the bed. Weeds are easy to control by use of mulch, some hand weeding, and a Round-up-killed, weed-free zone around the bed.

            The digging makes integration of the native soil and raised bed soil easier but it is serious hard work! I have found that the native soil under a raised bed loosens up well just from being covered by the raised bed.

            You can get quite elaborate in constructing the beds or you can keep it simple. I just lay the rock, cement blocks or railroad tie in place without any mortar or special fasteners. These materials are heavy enough to stay put. The Bexar County Master Gardeners have approximately 1000 raised beds constructed of landscape timbers arranged like “Lincoln logs” with 6” nails pounded into the overlap for their classroom gardens program. Another good way to keep landscape timbers in place is to drill a hole through all the timbers at the overlap and drive an 18-inch piece of concrete reinforcing bar through the drilled hole into the soil.

            Used railroad ties cost about $8 each. They do best when used for beds 8’ wide and in multiples of 8” for as long as you want. Landscape timbers are easy to cut out with a small chain saw or power saw so you can make beds in dimensions of less than 8’ easily. The landscape timbers cost under $4 each.

            Fill the beds with a special mix of compost, sand, and native soil. Many nurseries, and all of the landscape supply companies (Fertile Garden Supply, Garden-Ville, Keller Material, New Earth Technology, Living Earth Technology, etc.), offer a landscape light or raised bed mix for about $20/cubic yard. You can build your own with one part washed sand, one part compost, and one part soil.

            A cubic yard of soil is 27 cubic feet of soil or the amount that will almost fill a bed 1’ deep and 4’ by 8’ long. An 8’ by 8’ bed of used railroad ties (8”deep) take 1.5 cubic yards.

            Do not use regular soil for the beds, it will be difficult to work and poorly drained. Even the landscape mix in a raised bed will have to be replenished by compost every two or three years. I incorporate SAWS compost, leaves, or compost from my compost pile into the bed by using it as mulch between the rows or by digging it in row by row as vegetables are harvested or flowers replaced.

            For those of you that prefer to work raised beds with a tiller instead of a shovel, small gasoline and electric powered tillers exist just for the purpose. My little Mantis tiller would not last long in tilling native soil; but is light and compact, perfect for raised beds.