If you already have a garden plot, you can build "Raised Rows" (also know as wide-row gardening) to achieve many of the benefits of Raised Beds. In essence, raised rows are raised beds without a "container". Raised Rows demand the least amount of materials but are more labor-intensive. All you need to build them is a good garden fork or rototiller, a rake, a hoe and organic matter.
Step 1. Test your soil. The most accurate soil tests are done by your state's University Extension department. They will also provide you with specific instructions on what to add to your soil and in what quantities. Do-it-yourself kits are available at the resources listed at right and garden centers.
Step 2. Wait until your soil has dried enough to crumble in your hand. Remove all weeds, sod, trash and rocks. Spread organic matter such as compost, rotted leaves and decomposing straw over the garden plot. The quantity needed depends on the current state of your garden soil. At least 1 inch is a good start. Spread any soil amendments dictated by the soil test results. Work it all in to the depth of 8 - 12 inches using a garden fork or rototiller to create loose, crumbly soil.
Step 3. Mark the layout of your beds and paths using stakes and string. The beds should be no more than 4 feet wide (the ideal width is somewhat dependent on your reach -- see Step 4). Paths should be at least a foot wide and wider where you anticipate you'll be using a wheelbarrow or garden cart.
Step 4. Rake or hoe the soil from the paths up on to the beds, creating beds that are 4 to 6 inches taller than the paths. When one path has been completed (you don't want to walk on the planting area and compact it) it is easiest to stand in the new path, reach across the bed and rake the soil from the opposite path up on to the bed.
Step 5. Finish the paths with a shovel, dumping the soil into the middle of the bed.
Step 6. Level and smooth the top of the beds using the backside and right side of the rake.
Step 7. Line your paths with newspaper 5 sheets thick or cardboard (to kill any weeds underneath) and top with mulch, wood chips, straw, leaves or wooden planks.
Step 8. Mulch your beds too. It won't take long for weeds to find that lovely uncovered soil!
Step 9. Work compost into your garden soil every year, and keep it mulched.
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You may also appreciate these books on growing vegetable gardens.