Growing in raised beds has many advantages: It can be easier on aging backs and knees, and the soil conditions inside a raised bed can easily be kept optimal. By relegating external areas to the compaction of walking and wheelbarrows, the contained soil stays aerated, thus draining better. Raised beds can be maintained by simply topping with compost or mulch.
They extend a gardener’s growing season because the walls collect early spring sun and warm up before native soil, giving plants and seeds a jump on the growing season. I also like that my raised beds look tidy, since I mow right up to the wooden edge of the bed itself.
Determine where you want the beds to be and how large an area you want to grow in. While the sides can be as high as you’d like, raised beds should not be so wide that you can’t reach the middle from either side for planting, harvesting and maintenance.
Obtain the lumber to build the beds. This is often a complicated decision because of the many choices. In our Oregon area, cedar, while expensive, is the most common choice. When we lived in California, redwood was by far the most prevalent. Both of these woods have a natural resistance to rot and decay, which is imperative since they will be filled with dirt and water for their entire useful lives.
Another option is newer, recycled “lumber,” commonly known by the brand name Trex, which is a mix of sawdust and recycled plastic.
Pile It On
Exposure to light, wind and elements is important, but soil is also an important consideration. While it’s usually listed second to exposure, I personally feel it’s No. 1 in importance. It’s possible to change the exposure of your growing area, whether by selective tree trimming, shade cloth and screens, or planting hedges to reduce wind and increase warm microclimates. Soil, however, is a much more difficult thing to change. No one in their right mind wants to remove tons of native soil and replace it with imported, no matter how high quality. And even if this were possible, and not prohibitively expensive, some experts say that it’s impossible to completely rectify soil problems, particularly overall pH levels. I believe that piling on top of existing conditions is the best way to improve your soil, building it up with compost and beneficial amendments, much as happens in a deciduous forest. The easiest way to achieve this is with a raised bed.
Raised beds can be placed almost anywhere, provided other garden conditions have been met—good exposure and convenience for the gardener. If your beds are out of the way or difficult to get to, their regular care will fall to the wayside and success will be elusive. There are a few caveats when placing raised beds—ideally, you want to avoid placing them over the root systems of large, thirsty trees whose roots will invade the improved soil area and steal water and nutrients from the intended bed residents. If you have pernicious rodents like gophers or field mice, you can lay hardware cloth at the base to impede invaders. Other than that, beds can even be placed over excessively weedy areas or on solid subsurfaces like pavement, as long as protective underlayment or gravel to aid drainage is provided before filling.
Although expensive, this will last indefinitely and often can be bent into interesting shapes to increase visual interest. Other alternatives are stone, cinder blocks, fieldstone, bricks and more; pretty much anything, except treated lumber that can leach hazardous chemicals, can be used as bed edges.
Cut the material to the desired sizes for your bed walls. Remember to account for overlap at the ends. For sides that are longer than 4 or 5 feet, plan to have upright supports in the middle to prevent the longer boards from bowing out.
Drill pilot holes in the wood to prevent splits during assembly. Screw the wall pieces onto the support braces. Use screws instead of nails since screws will hold better as the wood shrinks and swells over time and seasons. Nails have a tendency to loosen and pop out.
With a helper, screw the side walls to the end walls. When complete, the raised bed will be ready to place.
Again with a helper, carry the finished bed to its intended location.
By having a “free-floating” bed, you can move it around and adjust it until you’re happy with the location. At this point, it can be left as is; the weight of the wood combined with filling will keep it in place. Otherwise, you can sink metal stakes inside the walls and secure them with pipe clamps prior to filling. This lends some additional support to the walls and prevents shifting of the finished bed. These pipes can also be used to support hoops or trellising. I salvage old metal pipe, but wooden stakes can also be used. Make certain they are a rot-resistant variety and screw them to the bed walls from the outside.
Put underlayment in the bed. This can be as simple as newspaper to block grass and other tenacious weeds or as elaborate as landscape cloth and metal mesh. On top of this you can place either manure or unfinished compost, which will eventually rot, providing roots with a nutrition boost, or simply fill the raised bed with planting soil or finished compost. If you start with unfinished compost, be sure to top it off with a fine-textured planting mix or finished compost when doing final planting.
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Enjoy! With regular mulching, you can keep the beds filled and see a happy, thriving population of earthworms and other beneficial organisms that perform the tilling and incorporating work for you.
This article first appeared in the May/June 2008 issue of Hobby Farms magazine. Pick up a copy at your local newsstand or tack and feed store. Click Here to subscribe to HF.