5 Tips for Raised Bed Gardens
BUILD AND TEST YOUR SOIL
Begin your gardening season with a soil test. This will identify what your soil has or lacks. In turn, you use this information to build your soil.
Start with the planting mix. Most of these are blends of peat moss, bark, and/or compost, and they help growers spoon-feed nutrients to their crops. However, mixes lack a high mineral content and do not provide all the nutrients needed for plants to thrive. Without a strong organic and mineral structure, the nutrients will leech through the soil before plants can use them. Correct this by adding compost to convert the blended mix into soil that holds nutrients, water, and oxygen for plants to use.
Although plants may require more fertilization in the first year or two of gardening, the need for added fertilizer decreases as you build the soil structure to the point where it retains nutrients.
“Good organic matter definitely reduces the need for fertilizer, so building the soil is important,” says Howard Eyre, DelVal’s associate professor for the landscape architecture department, adding “don’t neglect testing the soil’s pH. Consider the needs of your crop and adjust pH as needed based on your soil tests, not by guessing what the plants need.”
For example, blueberries require an acidic soil to thrive, but tomatoes (contrary to what many people will tell you) prefer a slightly acidic, almost neutral pH. Extremely high or low pH causes nutrients to lock up in the soil, and this can lead to plant discoloration, stress, and low yields.
Use solarization to rid the growing medium of soil-borne pests. By spreading a large sheet of clear plastic held in place with bricks, you can raise soil temperatures high enough to kill weeds, insects and their eggs, and various soil pathogens. Yes, this requires more time up front in preparing your beds, but this method can save you time, trouble, and expense later in the growing season when you have to deal with infected plants or damaging insects.
“Many people incorrectly think that solarization sterilizes the soil, and this will kill beneficial organisms,” says John Long, DelVal’s greenhouse manager. “But we regularly use this method in our greenhouse raised beds and enjoy reduced pressure from pests and weeds because of it. This method also provides a valuable lesson for our horticulture majors who use raised beds to schedule, sow, harvest, and weigh their production for a practical lesson in companion planting, crop rotation, and commercial vegetable production.”
Solarization is easier in warm climates, but even in northern regions you can use the method to heat the soil to around 110 to 125 degrees Fahrenheit for an extended period.
Years ago, growers used constant cultivation to stay ahead of weeds, but research has shown this can break down the soil structure that you worked so hard to build. So make use of plasticulture, the method in which you place black plastic over the soil and plant crops through it. Drip irrigation installed under the plastic provides proper moisture. This reduces the need for soil cultivation (weeding) and elevates the soil temperatures in the months when you would like to extend the season for temperature-sensitive crops.
If you are not into plastic and want to repurpose something from around the homestead, you can also use old carpet, wooden planks, bark mulch, or leaf mulch to discourage weeds. “Remember, weeds take vital nutrients and moisture from your plants and impede the harvest,” says Kristin Hulshart, DelVal’s director of the College’s Roth Center for Sustainable Agriculture in North Wales, Pa.
“As soil temperatures begin to heat up, your raised bed may also benefit from swapping the early-season fabric row cover or clear plastic row tunnels for a black woven shade cloth,” Hulshart says. “This can coax your cool-weather crops, such as strawberries, radishes, and lettuce, into producing a little longer into the heat of the summer.”
PLANT COVER CROPS
“Growing vegetables is very taxing on the soil and can strip away its nutrients,” says Scott Smith, assistant farm and horticultural production manager at DelVal’s South Campus Farm. “Planting cover crops in the off-season or between crop rotations adds back in these vital soil nutrients.”
Cover crops add significant organic matter, and future plantings benefit from the stored nutrients. These crops also improve soil structure by reducing compaction and opening up soil pores to store water and oxygen. Some of the more common cover crops are oats, buckwheat, rye, and clover.
GROW WITH WORMS
Worms are terrific little soil engineers. They break down raw organic matter into smaller pieces that beneficial fungi will make available to the plant’s root system. They also help blend organic matter through the soil, and their tunnels improve soil oxygen and water-holding capacity.
Consider building a vermicomposting bin with red worms to convert kitchen scraps into a nutrient-dense organic matter called castings, a great energy source for plants. You can also add night crawler worms directly to your beds to help build the soil structure.