Homegrown: Raised garden beds

Linn County Master Gardeners get quite a few calls about raised garden beds. Lisa Slattery, Linn County Master Gardener, Iowa State University Extension, provided the following information on this hot topic:

Last year was my first year gardening with raised beds.  I'm not sure what took me so long to start using raised beds but I'll never go back to the traditional “in the ground” vegetable garden.  

There are lots of advantages to raised bed gardening.  You have terrific, fertile soil from day one since you're not depending on the quality of your ground soil.  You never walk in the raised bed, only around it so you never compact the soil.  Plus raised beds are more user friendly – it's nice to sit on an overturned bucket to garden instead of bending down to reach the ground. 

This year I'm incorporating square foot gardening into my raised beds.  With square foot gardening you plant according to the space in one square foot, not in traditional rows.  Plants are closer together, so yield is higher and weeding time is less.  Vegetable plant spacing is dependent upon the size of your plant.  For example extra large plants like broccoli, cabbage, and tomato plants only have 1 plant per square-foot.  Large plants like leaf lettuce, Swiss chard, snap bush beans and cucumbers have 4 plants per square foot.  Spinach, beets and peas are planted with nine plants per square foot and small plants such as onion, radish and carrots can be planted up to 16 plants per square foot.  This is really tight planting, but that's the basis of square foot gardening.  Square foot gardening also lends itself well to staggering plantings so you have successive harvests.   

In order to do this method of gardening correctly you need a grid on your raised bed.  I love the idea of having a wood lath grid built, but I'm cheap and not too handy with power tools, so I have devised a grid using twine, which will wrap around screws that I have placed 12 inches apart on the perimeter of my raised bed.  My plant markers are old venetian blinds that I cut up.  

Next on my list is to build a protective cage to cover my raised bed.  With smaller beds, a chicken wire cover is easy to make with a wood base (if you're handy), but my raised bed is large so I'm planning to use flexible PVC piping to make a structure over the top to hold protective fabric in place to ward against spring frosts and pests.  Another item you need to consider adding to the raised bed is vertical frames for vine crops.  Build these on the north side of your raised bed so you don't shade other plants.  Choose materials with strength that can hold up quite a bit of weight, such as steel reinforcing rods with steel tubular pipe used for electrical conduit – it's strong.  Give square foot gardening a try this year – and I'll let you know how mine turns out too! - Lisa Slattery