For centuries, crops in many parts of the world have been grown on improved soils in elevated planting areas between sidewalks. This "raised bed" technology has been adapted for smaller areas and could be a viable solution to problems with poor soil conditions. Raised beds filled with a high-quality soil mix are also ideal for heavy metal or other soil-contaminated sites.
Raised beds can simply be formed into mounds, or framing material can be used to hold the soil in place. Each type has advantages and disadvantages. Frameless beds are less expensive, but the mounds are prone to erosion and take up more space. A framed loft bed is more space-efficient, but requires additional materials and labor.
For both types of raised beds, additional soil or organic material is required. Large quantities are required, so soil or organic matter should be readily available and relatively inexpensive. Some options include native soil removed from other areas of the garden or a bulk soil mix purchased from a garden center or landscape supply company. If your local soil is heavy and drains slowly, add organic matter such as finished home compost, purchased compost, composted leaves (leaf mold), or well-composted animal manure mixed with trash.
Stackable loft bed (without frame)
Frameless raised beds often require a lot of shoveling, sometimes for years. However, with a relatively simple process of soil improvement, the following methods can achieve good first-year garden yields.
If the soil is compacted, even if only 2 or 3 inches deep, an initial rototilling will help. Don't rush this step; wait until the soil is dry enough to crumble easily and no large clumps appear.
To create a mound, you will need to add additional soil and/or organic material. Spread a 2- to 3-inch layer of organic material over the soil surface. One cubic yard covers 162 square feet 2 inches deep, so you'll need 6 to 7 cubic yards per 1,000 square feet. Another option is to dig the sidewalk area (usually 14 to 16 inches wide) to a depth of 6 inches. Add the dug up soil to the top of the bed. Unless you are using a compost product, a mix containing compost, or a commercial enhanced planting mix, you will need to provide additional nitrogen fertilizer. A soil test is recommended to ensure adequate nutrient levels.
Rotary till to a depth of about 6 inches to mix in organic matter, soil, and fertilizer. Leveling achieves the same purpose, but using tillers is less work and the results are more even, especially in heavy clay soils.
Shape the bed with a shovel and rake (48 inches wide is common, but choose one that can easily access the center of the bed). This produces about 8 inches of soil and organic mix, enough for most vegetable plants to take root. When the elevated area is sloped, the natural slope of the soil will leave about 36 inches of flat planting space on top of a 48-inch wide bed.
Prepare the loft bed with the frame and
Compared to frameless beds, "retaining walls" or framed raised beds can be used to create special shapes, create barrier-free garden beds, and use space more efficiently.
First, determine your needs. How tall and wide do you want your bed to be? Make sure you can easily reach the plant in the center of the bed. A maximum width of 4 feet is a good choice for adult gardeners. Does the bed need to be accessible to children or people with reduced mobility? When choosing a framing material, consider your end use. For edible crops like vegetables, choose materials that won't leach chemicals into the soil (avoid railroad ties and old pressure-treated wood that may contain creosote or other chemicals). Cedar or rosewood are more expensive, but they are long-lasting, safe options. Concrete blocks or rocks can also be used.
Next, consider your location and plan for beds. Framed loft beds can be placed closer together than frameless beds, but you'll still need to incorporate walkways. Think about the type of equipment you need to move between beds; for example, will your trolley fit? Consider a plan for watering the beds. In-line irrigation systems are easiest to set up at this step, as they may require hoses to be placed in the bed before filling with soil. And consider the site preparation where the bed will sit. If there is already dense vegetation, it is best to remove it. One method is to physically remove the above-ground parts of the plant and dig up any large root masses.
Then, mark the area and build your loft bed. A frame bed can be as simple or as decorative as you wish (see Figure 2 for an example of a typical loft bed). Remember that the framing material needs to support the weight of the soil, plants and irrigation water. Beds longer than 6 feet or about 18 inches high should be reinforced (using crossover cables, anchor piles, or other mechanism) to help prevent the weight of the soil from pushing the planks outward
The next step is to fill up your loft bed. Purchase or prepare a soil mix that is high in organic matter. When using soil mixes, good landscaping companies offer separate mixes for different uses, for example a coarser mix might be fine for lawns but not for raised vegetable beds. Choose a mix that has good nutrition and water retention. If the framing material is on top of native soil, first dig or turn down at least 6 inches and mix the native soil into the soil mix as you fill the bed. Called "double digging," this is optional but loosens the soil to encourage plant root growth. A soil test is recommended so you can adjust nutrient levels appropriately and add supplemental fertilization if needed.
Caring for plants in raised beds
Whether you use organic or synthetic fertilizers, keep in mind that if you're growing vegetables in raised beds, these require a lot of nutrients. They grow quickly, taking only 25 to 100 days to develop a full plant and harvest a crop. Make sure to apply enough nitrogen, phosphate and potassium to feed the plants properly. Light green plants that require nitrogen may appear more frequently in raised beds than in traditional gardens. Add nitrogen fertilizer as needed during the growing season.
Water properly to keep the plants growing. The mixture of soil and organic matter in raised beds dries faster than clay. On the other hand, the soil is loose, so it absorbs water faster. A soaker hose or an inverted spray hose can be used. At low pressure, they will water anywhere in each row of plants.
Remember that a raised bed heats up and cools down faster than a floor bed. For year-round gardeners and those growing perennial vegetables, the taller the planting bed, the more frost protection is needed on cooler nights.
Maintenance of beds and sidewalks
Once shaping or framing is complete, keep traffic on the path and do not intervene or otherwise compact the prepared planting bed. Place stakes in the corners of frameless beds to prevent hose drag from damaging plants and damaging the bed. Organic matter breaks down and disappears, so add more often. Use compost to provide nutrients during the summer. Cover the beds with 2 inches of leaves or other organic material each winter. Material will break down well in spring and planting can proceed as planned.
Keep sidewalks as dry as possible to help control weeds. Add wood chips, bark, or paving stones to trails to prevent mud problems. Another option is to fill sidewalks with leaves when available. This will create a furrow for the compost material, which you can later rake into the bed.
Once the bed has gone through the improvement process, there is no need for rotary tillage. Conditions may not be ideal the first spring after the bed is established, but a light shovel or fork will create a suitable bed.
You can garden almost year-round as you keep adding more loose material. Planting can be done earlier because the improved drainage creates a better environment for the plants. It also promotes warmer soil and faster growth earlier in the season. At the end of the season, better drainage means healthier plants that will continue to produce longer. Sidewalks can provide better footholds after it rains. You're more likely to harvest cool-season crops with less dirt!
