This is ideal for carrots and other root crops that require extensive root penetration. To construct beds, rototill or dig until the soil is well loosened to at least six inches. Place two parallel strings four feet apart over the area to be planted, and shovel the loosened soil an both sides of the string onto the raised bed area. Add an inch or two of compost, and rake level. The result is a four foot raised bed that is 6-12 inches higher than the adjacent paths.
Some growers using raised beds frame their beds with wood.
While ordinary rough cut wood is the least expensive choice, it will rot out in a few years and need to be replaced. Eight inch cedar boards, which are rot resistant, are a better choice. Do not use pressure treated wood because the toxic wood preservative, chromium copper arsenate, will leach out and contaminate the soil. Steel corner brackets make the sturdiest frames. Raised beds, either framed or unframed, offer so many advantages that it is surprising that more backyard gardeners do not use them.