How to Care for the Soil in Raised Beds

Text by Mary Tiedeman, courtesy of the Soil Science Society of America.

As thoughts of spring enter our minds, many people are starting to design and develop their perfect spring and summer gardens. For many vegetable growers, beds are a great choice because the soil they contain warms up more quickly than ground soil, which can prolong the growing season. Raised beds promote soil drainage, provide adequate space for root growth and they can also be quite beautiful. Lastly, individual raised beds can be managed differently, which allows for growing plants that require specific soil conditions, such as blueberries that need acidic soil.

Temporary raised beds are tilled plots of land that extend 12 or more inches above the ground surface. They are not reinforced, so they must be reshaped over time, especially before each growing season. Permanent raised beds, on the other hand, are boxes made of brick, untreated wood or other safe, rot-resistant material. These beds can be developed to any height, but like temporary beds, they should contain at least 12 inches of soil.

Which choice is best for me?
Temporary beds are fitting for gardeners who can easily bend over for prolonged periods and who have plenty of yard space. These also work well where soils are uncontaminated, productive and easy to manage.

Permanent raised beds suit gardeners with limited yard space and soil that contains contaminants (such as lead) or presents challenges like a high clay content, low fertility, poor drainage, compaction and so on. Permanent raised beds are also a boon to those with physical limitations that make bending over a challenge, and those who simply enjoy the look of a contained bed.

Soil Maintenance
Once you’ve created your perfect raised bed, it is important that you maintain the health of its soil. The Natural Resource Conservation Service defines soil health as a soil’s capacity to function as an ecosystem that supports plants, animals and humans. Indicators of healthy soil include a loose granular structure, good drainage, moisture retention and a relatively dark color (influenced by organic matter). Here’s how to maintain soil health in your raised beds:

Avoid soil compaction. Compaction is the process of increasing the soil’s density by removing pores and damaging soil structure. This makes it difficult for roots to grow and limits roots’ access to water, air and nutrients. The number-one rule for reducing compaction is to never step or kneel on your garden soil. To reduce this desire, design garden beds that are no more than four feet wide. Also, mulch the paths surrounding your beds. This will highlight their location and will provide padding for the soil.

Promote soil drainage. For both temporary and permanent raised beds, this can be done by digging beds that are deeper than 12 inches. Tilling to deeper depths may prevent water from ponding around the root zone, unless you are already working with very wet soils. (If you’re dealing with contaminated soils, please first seek professional guidance before developing a permanent raised bed.)

Amend your soil with organic matter every spring. Organic matter is a great source of slow-released plant nutrients. It encourages soil structure to develop by holding soil particles together like glue. It also attracts beneficial organisms, which also help develop soil structure. Structural development improves water infiltration, gas exchange and increases soil’s resilience to compaction.

Cover your soil, especially during the off-season. Naked soil is vulnerable to wind and water erosion. Both processes effect soils in different ways, but both lead to loss of soil and organic matter, reduced water infiltration and structural loss. Cover crops are a great solution, as they also provide additional nutrients to your soil when they are tilled into the garden bed before planting crops in the spring. Mulching with leaves or straw is another viable option, as these are easily accessible, decompose relatively quickly and effectively cover soil.

Managing for soil health is one key step toward having a successful garden this summer. Avoiding compaction, digging deep, applying organic matter and keeping the soil covered are simple measures that will reap great rewards.

Soil scientist Mary Tiedeman is a Research Assistant at Florida International University. This article is presented by the Soil Science Society of America. Learn more at soilsmatter.wordpress.com.

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