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 to smaller areas and can be a viable solution to the problem of 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 form mounds, or a framing material can be used to hold the soil. Each type has advantages and disadvantages. Frameless beds are less expensive, but mounds are prone to erosion and take up a larger footprint. A loft bed with a frame is more space efficient, but requires additional material 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 moved from other areas of the garden or a bulk soil mix purchased from a garden center or landscape supply company. If your native 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 litter.
Ready to stack loft bed (frameless)
Frameless loft beds often require a lot of shovels, sometimes years. However, following a relatively simple soil improvement process, the following methods can achieve good garden production in the first year.
If the soil is compacted, even if it's only 2 or 3 inches deep, initial rotary tillage can help. Don't rush this step; wait until the soil is dry enough to easily crumble 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 will cover 162 square feet 2 inches deep, so you need 6 to 7 cubic yards per 1,000 square feet. Another option is to scoop the walkway area (usually 14 to 16 inches wide) to a depth of 6 inches. Add the excavated soil to the top of the bed. Unless you use a compost product, a mix containing compost, or a commercial fortified planting mix, you will need to provide additional nitrogen fertilizer. Soil testing is recommended to ensure adequate nutrient levels.
Rototill to a depth of about 6 inches to mix organic matter, soil and fertilizer. Spading achieves the same goal, but using a tiller makes the job less taxing and results are more uniform, especially in heavy clays.
Use a shovel and rake to shape the bed (48 inches wide is common, but choose one that can easily go into the center of the bed). This produces about 8 inches of soil and organic mix, enough for most vegetable plants to take root well. When the elevated area slopes, the natural slope of the soil will leave about 36 inches of flat planting space on top of a 48-inch-wide bed.
Preparing a loft bed with a frame
Compared to frameless beds, "retaining walls" or raised beds with frames can be used to create special shapes, create accessible garden beds, and use space more efficiently.
First, determine your needs. How high and wide would you like the bed to be? Make sure you have easy access to the plants in the center of the bed. A maximum width of 4 feet is a good option for adult gardeners. Does the bed need to be accessible for 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 site and plan for beds. A framed loft bed can be placed closer together than a frameless bed, but you'll still need to incorporate sidewalks. Think about the type of equipment you need to move between beds; for example, will your trolley fit? Consider your plan for watering the bed. In-line irrigation systems are easiest to set up at this step, as they may require water hoses to be placed in the bed before filling with soil. And consider site preparation where the beds are located. If there is existing dense vegetation, it is best to remove it. One way is to physically remove the aerial parts of the plant and dig out any large root pieces.
Then, mark the area and build your loft bed. Frame beds can be as simple or as decorative as you wish (see Figure 2 for an example of a typical raised bed). Remember that the frame material needs to support the weight of the soil, plants and irrigation water. Beds longer than 6 feet or taller than about 18 inches should be reinforced (using crossover cables, anchor stakes, or other mechanisms) to help prevent the weight of the soil from pushing the boards outward
The next step is to fill up your raised bed. Buy 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 mix with coarser soil might be fine for lawns, but not for raised vegetable beds. Choose a blend with good nutrition and water retention. If the framing material is on top of native soil, first dig down or rotate till at least 6 inches and mix the native soil into the soil mix as the bed is filled. Called "double digging," this is optional but loosens the soil to encourage plant root growth. Soil testing 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 use raised beds to grow vegetables, these require a lot of nutrients. They grow rapidly, producing a complete plant and crop for harvest in just 25 to 100 days. Make sure to apply enough nitrogen, phosphate and potassium salts to feed the plants properly. Light green plants that require nitrogen may appear more frequently in raised beds than in traditional gardens. Nitrogen is added as needed during the growing season.
Water properly to keep plants growing. The mixture of soil and organic matter in a raised bed dries faster than clay. On the other hand, soil is loose, so it absorbs water faster. A soaker hose or an inverted spray hose can be used. With low pressure, they will water where you want on each row of plants.
Keep in mind that raised beds will heat up and cool faster than ground beds. For year-round gardeners and those who grow perennial vegetables, the higher the raised bed, the more frost protection is needed on cool nights.
Maintain beds and walkways
Once molding or framing is complete, maintain traffic in 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 degrading the bed. The organics break down and disappear, so more often is added. Use compost to provide nutrients in the summer. Cover the bed with 2 inches of leaves or other organic material each winter. The material will break down well by spring, and planting can proceed as scheduled.
Keep sidewalks as dry as possible to help control weeds. Add wood chips, bark, or paving stones to the trail to prevent mud problems. Another option is to fill the walkway with leaves when available. This will create a trench for compost material that you can rake into the bed later.
Once the bed has gone through the improvement process, there is no need for rotary tillage. Conditions may not be ideal in the first spring after the bed is built, but a light shovel or fork will create a suitable seedbed.
As you keep adding more loose material, you can garden almost year-round. Planting can be done earlier because the improved drainage creates a better environment for the plants. It also promotes faster soil warming and faster growth early in the season. At the end of the season, better drainage means healthier plants that will continue to produce longer. After it rains, sidewalks can provide a better foothold. You are more likely to harvest cool season crops with less dirt!
