Building Raised Beds

If you prefer, once the soil underneath is loosened (via trenching, bastard trenching, double digging, a digging fork, mounding with a rake after tilling, or even just tilling), you can also make raised beds to corral your loosened soil and even to hold added soil—or just to delineate the bed areas if you’re only tilling—using several different methods and materials. However you build or use them, raised beds are relatively easy to make. 

One can make a raised bed out of just about anything and mitigate the deficiencies with clever strategies, so there’s no need to specify any one kind or type of material. You can use boards, timbers, straw bales, concrete blocks, bricks, stone, or whatever other material you prefer, fastened together in a way that makes the most sense for that material and your purposes. For example, boards are often nailed or screwed together for more permanent beds, but stakes pounded into the ground on the outside to hold boards or timbers against the soil can also be used for beds on which you’d prefer easy disassembly. Similarly, straw and concrete blocks can simply be stacked together and supported by stakes as needed.

If using boards, you can use nominal one-inch or two-inch lumber, from four inches to twelve inches wide, to get the particular height and stiffness you desire. Nominal two-inch-thick boards, being a fair bit sturdier, are often a nice choice for longer beds—timbers are overkill but might be wanted to for a certain aesthetic—but stakes pounded into the ground can stiffen and support nominal one-inch lumber as needed. Obviously, wider boards, up to nominally twelve-inches wide, give much greater depth for roots if soil is being added. Four-to-six-inch-wide boards are usually plenty if just delineating an area or holding in mounded soil in a double dug bed. Most don’t use any structure around double-dug beds, but it would make sense if someone would.

If you’re using untreated wood or straw, they will rot faster. If you’re using treated wood, it’ll last longer, but I’d advise looking up the research on its effects on health when used near garden vegetables and making up your own mind. If it doesn’t break, concrete will last the longest, but it’s heavy to lug around the garden and often a bit too bulky, interfering with path space. 

Many people choose to use the added height of their structure to contain added loosened soil. If that’s the case for you, fill this structure with the best soil you can find.

Raised beds have a few downsides: Being flat on top instead of curved, they don’t have as much surface area for planting as a double-dug or raked mounded beds, nor, for the same reason, do they let as much oxygen into the soil. Even though it’s covered by the sides, having so much of their soil above ground, raised beds can also dry out quickly. Further, when people use them directly on unprepared soil or sod, they don’t have soil loosened beyond what is contained inside their structures. We know plants need soil loosened much deeper than this. Likewise, permanent raised beds make it very difficult to loosen the soil deeper than their bottoms once they’re in place. Finally, the wood and straw structures break down over time, needing the cost of replacement, and pulling nutrients out of the garden in the process of decomposition. 

Many of these deficiencies, however, can be cleverly mitigated. As mentioned, the soil underneath should be loosened before placing the bed, and a digging fork or broadfork can be used to loosen the soil up to 12 inches once the bed is in place (or you can make a longer-tined digging bar to loosen the soil 18 inches). It may be difficult, but one could even double dig inside of a permanent raised bed. Mulch can be applied to the top of the soil to limit evaporation, and the bottom of the structure can be dug into the ground enough to keep water from spilling out of the bottom when watered and help mitigate moisture loss in general. Soil inside can also stay mounded. As mentioned, one can even use a raised bed structure around a double dug bed without piling in more soil, especially one designed for easy disassembly when it’s time to re-dig the bed. 

Aside from these solvable deficiencies, raised beds have some benefits as well. In fact, some of the same characteristics that causing deficiencies, create benefits as well. Being above the surrounding soil, for example, may cause them to dry out faster, but it also causes them to be warmer earlier in the spring, a boon for those who want to plant a little sooner. Plus, being drier is welcomed when the surrounding soil is particularly wet. Likewise, raised beds give a holding place for better soil when one thinks the underlying soil is really bad. I’d say, “Improve that soil; it’s already there containing a wonderful starting ground of available nutrients and micro-organisms.” However, others may prefer just adding soil above. To each one’s own.

Raised beds may have both detriments and benefits, but, if you mitigate the detriments, they may be right for you. If you’re interested in them, experiment with several options, and find the best methods for you.

And have fun in the process!

However you build your raised beds and loosen your soil, adding cured compost is the best way to add the organic matter your plants need to be truly healthy.