Garden Doctors: Raised beds are more efficient

Alice S. of Santa Rosa asks: I have gophers and need to plant my vegetables in raised beds. What general information can you give me about sizes and shapes?

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Concentrate on small areas where you amend and prepare the soil. Raised beds warm up quickly in spring and stay warmer longer through the summer and fall; they limit foot traffic to the walkways between the planting beds, thereby reducing soil compaction; and they help conserve water. Raised beds facilitate better drainage, are easy to cover for spring and fall frost protection, can be shaded during the hottest part of summer and are ideal for enabling people with limited mobility to garden.

Although planting beds require more frequent watering due to more plants per square foot, a raised bed is more efficient overall. It results in higher yields for the amount of water used.

Raised beds make it easy to create a deep, fertile soil high in organic matter. They allow you to completely amend your native soil, which is the ideal situation, or to bring in any soil mix you’d like to fill the beds. These beds are usually 4 feet wide and can be as long as you want. The height can be almost any dimension, although 12 inches seems to be the norm and allows for good root development. This should be the minimum height when working with hard native soil.

To accommodate those gardeners with special needs, the bed height can be raised to minimize bending or to allow gardening work from a wheelchair. Remember to plan a walkway space between the beds that’s wide enough to accommodate specialized equipment for mobility.

You can make raised beds without sides. Simply mounding soil creates a “raised” bed. Walkways are dug down with the soil thrown up onto the bed. This type of bed is also usually 4 feet wide at the base and 3 feet wide at the top and amended with organic mulch to prevent soil erosion and to reduce any compaction from rain and sprinkler irrigation.

When building a frame, most gardeners tend to use rough-sawn cedar or redwood 2-by-12-inch boards, but you don’t have to use landscape timber - concrete blocks or “plastic wood” work well, too.

Think about which direction you should lay out the beds. For frost protection, an east-west orientation has a slight advantage of collecting heat, which is a good thing. For summer crops, a north-south orientation holds the slight advantage of sunlight on both sides of the plant row each day. Because there’s really no clear advantage overall, orient your beds in whatever direction works best for your landscape design.

Do not line the bottom of your frame with plastic. The lining will impede good drainage.

Because you have gophers, lay hardware cloth or 3/4-inch mesh poultry wire under raised beds before planting. It should go up the insides of the walls at least a foot.

Do not use CCA pressure-treated lumber (due to arsenic concerns) or railroad ties (creosote-caused cancer concerns) to build raised beds. Both can lead to environmental and health issues.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.