For centuries, crops in many parts of the world have been grown on improved soils in elevated planting areas between sidewalks. This "raised bed" technique has been adapted to 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 sites contaminated with heavy metals or other soils.
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 mounds are prone to erosion and take up a larger footprint. 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 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 slow-draining, 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 (frameless)
Frameless raised beds often require a lot of shoveling, sometimes years. However, with a relatively simple process of soil improvement, the following methods can produce good garden yields in the first year.
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 that it breaks up easily and doesn't appear in large chunks.
To create mounds, you 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 walkway 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. A shovel accomplishes the same goal, but using a cultivator is less work and the results are more even, especially in heavy clay soils.
Use a shovel and rake to shape the bed (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 in a 48-inch wide seedbed.
Prepare the loft bed with the frame and
Compared to frameless beds, "retaining walls" or raised beds with frames can be used to create special shapes, create barrier-free garden beds, and use space more efficiently.
First, determine your needs. What height and width 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 food crops like vegetables, choose materials that won't leach chemicals into the soil (avoid railroad ties and old pressure-treated lumber that may contain creosote or other chemicals). Cedar or redwood are more expensive, but they are long-lasting, safe choices. Concrete blocks or rocks can also be used.
Next, consider your site and plan for beds. Framed loft beds can be placed closer together than frameless ones, but you'll still need to incorporate walkways. Consider the type of equipment you will need to move between hospital beds; for example, will your trolley fit? Consider your plan for watering the beds. In-line irrigation systems are easiest to set up during this step, as they may require water hoses to be placed in the seedbed before filling with soil. And consider the site preparation where the bed is located. If dense vegetation is present, 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 fragments.
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 raised bed). Remember that the framing material needs to support the weight of the soil, plants and irrigation water. Beds longer than 6 feet or taller than 18 inches should be reinforced (using cross 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 mix with coarse soil may 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 until at least 6 inches and mix the native soil into the soil mix as you fill the bed. This is called "double digging," and it's 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, remember that if you're growing vegetables in raised beds, you need a lot of nutrients. They grow quickly, taking only 25 to 100 days to develop a full plant and crop ready for harvest. Make sure to apply enough nitrogen, phosphate and potassium to properly feed the plants. Light green plants that require nitrogen may appear more frequently in raised beds than in traditional gardens. Add nitrogen 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 where you want them on 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 higher the raised bed, the more frost protection is needed on cooler nights.
Maintain beds and walkways
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 reducing the quality of the bed. Organic matter breaks down and disappears, so more frequent additions are required. Use compost to provide nutrients during the summer. Mulch the bed each winter with 2 inches of leaves or other organic material. By spring, the material will be well decomposed 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 the walkway with foliage where 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, rotary tillage is no longer required. Conditions may not be ideal the first spring after a bed is established, but a light shovel or fork can create a proper 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 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. Sidewalks can provide better footholds after rain. You're more likely to harvest cool-season crops with less soil!
