CORVALLIS — Afraid gardening and your soil are not compatible? Raised beds can come to the rescue.
"By building raised beds, you instantaneously can have good garden loam," said Ross Penhallegon, a horticulturist with the Oregon State University Extension Service. "Raised beds answer the question of how we garden in inhospitable areas that are too sandy, too wet or have too much clay."
April is a good time to build raised beds. First select the plants you want and learn how deep their root systems grow. Raised beds are generally six to 12 inches high depending on the depth of the plant's roots, Penhallegon said. Raised beds are typically three feet wide so you can reach across easily to weed and maintain the plants, he said. The bed can be as long as you want.
After you build the structure framing the raised bed, fill it halfway with loam. Using a three-tined garden fork, mix in an equal amount of organic matter such as compost, leaf mulch or animal manure. After the first season of growing vegetables in the raised bed, add two to four inches of compost in October. Then in March or April, mix the compost into the soil using a garden fork.
To build your raised bed, Penhallegon suggested using the following materials:
- Straw bales —Use straw from wheat, barley or other grains but do not use hay because it can contain weeds and seeds, he said. Bales should be free-standing. Dig a hole in the straw for each plant. The bales are especially good for growing carrots and potatoes. You can also plant peas or pole beans in them if you use a trellis. Fertilize and water by hand or use a soaker hose. The straw slowly composts for the plants, feeding them nutrients.
- Raw wood — Cedar is a good choice because it is fairly resilient, Penhallegon said. Coat boards with exterior latex paint, which is not as strong as chemical preservatives and can resist moisture. In choosing between raw and treated wood, decide how often you want to replace the wood, as it decays faster when wet, he said.
- Treated wood — Wood that is treated with preservatives such as pentachlorophenol, creosote and linseed oil lasts longer in rainy climates, Penhallegon said.
Research shows that there is little likelihood of wood-preserving substances contaminating the soil, he added. Nevertheless, he still advised covering the wood with plastic sheeting or exterior latex paint to reduce the risk.
- Old tires — Old tires stacked on top of each other work especially well for potatoes.
- Concrete blocks — Concrete lasts a long time, absorbs heat well and is water-resistant, Penhallegon said. Stack one, two or three blocks high. Keep in mind that it is more expensive than wood. Look for inexpensive blocks that are cracked or chipped, he said.
- Railroad ties — Whether railroad ties are safe to use is hotly debated among researchers and the general public, Penhallegon said. "It's been shown that there is very little creosote leakage out of railroad ties," he said, "but that depends on how old they are, whether they're damaged and how long they've been around. It's very tough to say absolutes." He recommends covering railroad ties with plastic sheeting to protect your plants.
OSU Extension's "Growing Your Own" guide at http://bit.ly/T0vIYv offers suggestions for building raised beds.
Also check out Extension's guides "Raised Bed Gardening" at http://bit.ly/UxPfmA and "How to Build a Raised Bed Cloche" at http://bit.ly/Z4XFB0.