A bed should be no wider than 4 feet, but length can be whatever suits the site or gardener's needs. Wider beds can be subdivided into sections accessible from planks or stepping stones.
The bed does not have to be enclosed or framed, but if unframed, the use of power tillers is feasible. Framing offers several other opportunities, however; and a properly maintained bed will not need power cultivation.
The benefits of raised-bed gardening include improved soil conditions; ease of working and pest control, and saving water. Soil compaction can reduce crop yields up to 50 percent. Water, air and roots all have difficulty moving through soil compressed by tractors, tillers or foot traffic.
Raised beds also help in situations where compaction is not the only problem. Homeowners might have low spots unsuited for conventional gardens because of poor drainage or excessive erosion from runoff.
There are few guidelines to remember in raised bed construction:
Keep the beds narrow and match their length to the site and the watering system.
A north-south orientation is best for low growing crops, allowing direct sunlight to both sides of the bed.
Beds that contain taller crops such as pole beans, trellised peas or caged tomatoes might do better on an east-west axis. Thus, lower growing crops could be planted on the south side of the bed and still get full sun.
Avoid the use of creosote or pentachlorophenol treated lumber for bed frames. These chemicals can leach out and injure plants. Use redwood, cedar, cement block or brick, or recycled plastic.
The depth of the soil should be at least 6 inches. Fill the bed with top soil mixed with 2 to 3 inches of compost.
