University of Vermont Extension 
Department of Plant and Soil Science

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RAISED BEDS
 
Dr. Leonard Perry, Extension Professor
University of Vermont

         
Raised beds can be any shape and form, from a simple mound of soil to elaborate ones a foot or more high with wooden sides—basically elaborate and large, generally non-mobile containers.  They make gardening much easier, especially for those less agile or with physical challenges.  The off season, fall or early spring, when garden chores are less (like weeding and watering), is a good time to build such beds.
           
Since raised beds are above ground, they heat up sooner in the spring.  But, on the flip side, they cool down more quickly in fall and can get quite cold in winter so are not suitable for tender plants nor most perennials.  Many gardeners with clay or poorly draining soil find these beds make successful gardening possible.  If for vegetables and most flowers, site in full sun or with at least 6 hours of sun per day.
           
Perhaps the simplest raised bed has straw bales for the sides, the center filled with soil.  The straw will eventually break down, leaving a mounded berm of soil unless you reconstruct them every couple of years.
           
Most gardeners use lumber for the sides, either 2-inch by 8-inch or wider boards.  You can connect the ends with lag screws (nails tend to pull out), or buy corners just for this purpose.  These corners, available from some garden retailers and online, are often sturdy plastic, push in the ground, and have slots to hold the boards.  Make sure the soil where the boards will rest is level.  An advantage of lumber is that you can affix hoops, such as from flexible plastic piping or sturdy wire,  on the sides to hold shade and frost cloth.
                         
If you have at least decent soil, you can usually get by with a 6- to 8-inch high side.  If poor soil, you’ll want at least a 12-inch depth for rooting of most vegetables.  Don’t make beds more than about 24 to 30 inches wide, if accessible by only one side, or twice that if you can reach from both sides. If you want to sit, particularly on taller beds, make sure you have a board or width on top of sides for this.
           
When choosing lumber, avoid creosote treated railroad ties.  Many gardeners also avoid  pressure-treated wood so any chemicals won’t leach into the soil, particularly if vegetables are to be grown.  You can spend a bit more money for composite materials such as made from sawdust and recycled plastics, which will last for many years.  If you have a local lumber mill, check for natural woods such as cedar. Some home and garden stores have raised bed kits in the spring with all the supplies you’ll need, or perhaps even already built.
            
If you’ll have more than one raised bed, you can get quite creative with shapes if you time and skills allow.  Otherwise, a simple rectangular bed is easiest to construct.  Allow plenty of room between beds for movement.  I have 3 feet between mine for carts, and for me to maneuver while weeding and harvesting.  This also might be good for wheelchairs and mobility carts.  For these, also plan space for turning around, hard surfaces, and no more than 5 to 8 percent grade.
           
For the paths between beds, I use a thick layer of newspapers covered with straw.  The newspapers help with weed control, and decompose after a year.  Weed control fabrics could be used instead for longer control    The straw is the same that I’ve recycled from covering garlic or other winter crops in the beds. Or, you might use bark, wood chips, or similar.
           
Once you’ve constructed the bed sides, fill with a good quality topsoil amended with plenty of compost or composted manure.  Especially if your beds are large, you may want to buy bulk soil or have it delivered.  Make sure you mix these together well with a garden fork or hoe, or by turning.  Particularly if the native soil beneath the beds is poor, break it up somewhat first with a fork.
           
Raised beds will dry out faster than field soils since they are raised and more exposed.  Use mulches on crops, soaker hoses, and check frequently for watering. 
           
Once the season is done, I clean up my beds so they are ready for spring.  Test the soil every few years, and add lime if needed in fall.  I also add an inch of compost on beds in fall after they’re cleaned so they’re ready in spring when I’m much busier.  But you can add compost just before planting instead.  I wait until spring, or before planting, to mix in some organic, dry fertilizer.
                 

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