More on raised beds

In the Garden

Ralph Purkhiser, Purdue University Master Gardener

     Last week, we began a discourse on raised beds.  We discussed the advantages of beds of different heights and noted that a raised bed of any height allows the gardener to control the type of soil in which he or she will garden.   As promised, this week we will look at bed shapes and building materials.

     Raised beds may be build using a variety of materials.  Of course, wooden beds come to mind first.  Beds may be constructed as boxes, or they may be built using metal or plastic corners that accept boards of a certain size.  Railroad ties are often used to construct raised beds, but I do not recommend using the ties for beds where edible crops will be raised.  The creosote will leach into the soil and could contaminate your food.  The same goes for treated lumber.  While the treated lumber available now is not made using dangerous chemicals, I am personally still leery of using it for vegetables.  I have always used cedar or fir boards.  I have some beds made of native red cedar lumber that have been in use for more than a decade and are still in pretty good shape.

     I also have several metal beds.  Some are old metal stock tanks that have been transformed into beds.  Others were bought as raised bed kits.  The metal beds are also holding up well.  Old tires, especially tractor tires with the sidewalls cut out, have been used for raised beds on farms as long as tractors have been used.  It is good recycling and the heavy tires were often the only way to protect ornamentals from the mowers.

     Several types of plastic beds have been introduced on the market.  Some snap together like fake lumber.  Others are molded into specific shapes.  There are even some plastic grow bags that have been introduced that can be filled with soil and used as free-standing beds.  They range in size from containers for a few plants to beds as large as twelve feet long.  The problem with plastic beds is that plastic tends to grow brittle after being out in the weather for a short time.  String trimmers also may destroy a bed.

      Straw bales may be used to construct beds.  In the past, I have dedicated a column to straw-bale gardens, so I will not go into details here.  However, the drawback with straw bales is that they will only last a couple of seasons.

      For something a little more permanent, beds may be constructed using concrete blocks, bricks and natural stone.  Capstones may be used to form seating atop the concrete blocks, allowing one to tend the bed from a seated position. 

     Finally, one may build a raised bed or berm using just soil.  The soil is mounded in the center of the bed and tapered down to the level of the surrounding ground.  Sometimes, edging may be added to hold the soil in place.

     Whatever material used, the size of a bed is important.  A raised bed should be narrow enough to be cultivated without stepping into the bed.  I usually like to keep beds no more than four feet wide.  If the bed is against some surface and must be tended from only one side, I keep it to no more than two feet.

     Beds may be made in any shape.  Squares and rectangles are more formal and orderly.  Most vegetable gardeners tend to use rectangular beds, often creating rows of similar size and shape.  Curved lines are less formal and are more relaxing.  Kidney-shaped beds are common, but beds may take any shape to fit in the overall landscape

      Go ahead and site a bed or two for next year.  Use a garden hose or some rope to lay out the shape before covering the ground with cardboard.  You may use scrap lumber, rocks or other items to hold the cardboard in place until you cover it with the soil.  Building your bed now will give you a good head start next spring, when the beds will be ready for plants.