Thinking about a raised-bed garden?

By Carol Holmquist
Extension Master Gardener
University of Vermont
Maybe this is the year that you will finally decide to put in that raised-bed garden. Raised beds can add a designated gardening area to your yard. They also can be installed in areas that are difficult to garden conventionally such as sites with shallow soil (over rock), steep slopes or poor soil quality. 

Raised beds can have soil structure and drainage that allow the soil to warm up earlier in the season and give you a head start on spring. Stubborn perennial weeds can be less of a problem in raised beds than in other gardens.

The simplest form of raised beds is the flat-topped mound, usually six to eight inches high, which requires no materials other than additional soil. Alternatively, you can edge your raised bed. This will give it definition as well as put a barrier between the garden and the lawn and prevent perennial weeds from creeping into your plantings.

For a more stylistic look, build raised beds with other materials. Do not use treated wood for edible crops. Alternatives to treated wood include wood that is naturally resistant to decay (cedar, redwood, and black locust), synthetic products made of recycled plastics, rock or masonry block. All of these provide sturdy structures that should persist for a long time in the landscape. 

You can make soil for your raised bed from your own garden soil. Add four to six inches of finished compost, peat moss or well-rotted manure and thoroughly till it into the soil. I use 50 percent screened topsoil and 50 percent high-quality compost, but you also can purchase high-quality potting soil, similar to what you would use for container gardening. 

Different vegetables like different pH levels, so be sure to run a soil test on your bed and amend your soil to support the vegetables you intend to grow. You can order a standard or field soil test through the University of Vermont  Agricultural and Environmental Testing Laboratory in Burlington. For the form and instructions visit go.uvm.edu/ag-testing.

If you are not using field soil in your beds but rather more of a potting mix, you will need a saturated media test, available from the University of Maine (umaine.edu/soiltestinglab). Request the basic high tunnel test, and indicate on the form that the test is for raised beds.

You can grow most vegetables in your raised bed, but here are a few things worth noting. Plants that spread easily (mint) or need a lot of room (squash or melons) may take up a lot of your space. For vegetables such as carrots, parsnips, beets and turnips that have significant tap roots, make sure your raised bed has the depth to accommodate the particular variety you intended to plant. Or choose miniature varieties of these vegetables. 

For more information, call the UVM Extension Master Gardener Helpline toll-free at (800) 639-2230 or (802) 656-5421. Or consider becoming a Master Gardener (www.uvm.edu/extension/mastergardener). Registration for the next course opens in November.