1. Raised floor bed
The simplest raised beds are flat-topped mounds, usually 6 to 8 inches tall. They don't require any materials other than extra soil.
Introduce additional soil to form the beds, or dig three to four inches of soil from the paths between the beds. If you're introducing additional soil, make sure it's not from an area where soil-borne plant pathogens or contaminants like lead and pesticides are present. Whether you dig out the aisle or not, make sure the aisle area around the raised bed is at least 24 inches wide.
Start by determining the size of your raised ground bed. If you only have access to one side of the bed, the maximum width should be 2½ feet. The bed can be up to five feet wide if you can access it from both sides. The length and shape are entirely up to you.
To make the bed itself, add 4 to 6 inches of finished compost, peat moss, or well-rotted manure to the existing area. Thoroughly until it gets into the soil below. Farming on raised beds will not be a normal practice. Shape the tilled soil into a flat mound about 8 inches high, tapering the sides at a 45-degree angle. Let the soil rest for a week or two before planting.
Avoid stepping on raised beds, which can compact the soil. Use a hoe to remove weeds from the center of the bed. Likewise, lean on a hoe to harvest from the middle of the garden. Try to keep the sides of the mound intact so your raised bed doesn't slide down the trail.
As the seasons go on, the soil settles, but the mounds remain. Once created, raised ground beds only need a slight makeover with a rake at the start of each season. Organic matter is added to the surface as mulch each season during the growing season or after harvest. Earthworms and other soil organisms carry it into the soil, so no farming is required.
2. Supported Raised Garden Beds
Create a vital barrier between your garden and lawn, the largest source of perennial weeds, around the edge of your raised bed. Frames, whether wood, stone, brick or plastic, add a neat, complete look. Some gardeners also leave four inches of bare or covered soil around the bed to make mowing easier.
When deciding on the shape and size of a support loft bed, keep in mind that some edge materials only allow angular corners. Prepare the soil as before, but place the frame around the bed before raking the soil into shape.
Unlike unsupported beds, you can make supported loft beds wider than five feet. A sturdy wooden edge can support a wide plank used as a bridge to move from one part of the garden to another so you can reach the center of the garden without stepping on the soil.
To make a wooden frame, cut 2"x6" untreated rot-resistant wood, such as cedar. Railroad sleepers are not a good choice for loft beds unless the weathering is very good. Railroad sleepers treated with creosote are toxic to plants. Wood treated with copper, chromium and arsenic (CCA) is also harmful to vegetable crops, as some of the arsenic may leach from the wood and into the plant.
Turn the planks "in" so that if they warp, they bend slightly outward in the middle. Secure the corners with decorative screws. Remove or add soil as needed to ensure the frame is level. Once the frame is in place, spread the soil evenly over the top. Now you can plant directly to the bedside. You'll have more room to grow than a raised ground bed in the same area because you don't have to maintain sloping sides.
3. Container Raised Garden Bed
Raised beds with 10-inch to 12-inch walls provide more protection for plants in high-traffic areas near sidewalks. In paved areas where reflected heat can stress plants, raising the bed a foot or two can reduce heat. Raised beds with taller walls maximize physical accessibility and reduce maintenance. 27" is a comfortable working height for most wheelchair users, but you can customize the bed to any height. Choose a width that matches the reach of your arms.
To make a 27" tall planter, place a 2"x4" and three 2"x8" planks horizontally and a 2"x4" plank vertically for reinforcement, especially in the corners. Build the sides first and turn the planks again to have the "heartwood in." Use decorative screws to attach the vertical stiffeners and attach the corners. You can make a seat stand by laying a 1"x4" board flat on top of the frame, extending it to the sides.
Fill the planter with a mixture of soil and organic matter, adding 2 to 4 inches per year as the soil settles and ages. Remember that even large containers require extra watering.
