How do I keep soils in my raised bed healthy?

As thoughts of spring enter our minds, many people are starting to design and develop their perfect spring and summer gardens. If you are new to gardening, you should know that there is no “right” way to design a plot. There are countless options! This fact allows you to embrace your creative side and build a garden that best suits you and your environment.

Raised beds add a flexible option where space or poor soil are limitations. Credit: Morguefile

Of the options available, raised beds are very common. Raised beds are a great choice because their soils warm up more quickly, which can prolong the growing season. Raised beds promote soil drainage, provide adequate space for root growth, and can also be quite beautiful. Lastly, individual raised beds can be managed differently, which allows for growing plants (such as blueberries) that require specific soil conditions. Two types include temporary and permanent raised beds.

Temporary raised beds are tilled plots of land that extend 12 or more inches above the ground surface. They are not reinforced, so must be reshaped over time, especially before each growing season. Permanent raised beds, on the other hand, are contained in boxes made of brick, untreated wood, and 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 if:

• You can easily bend over for prolonged periods
• You have plenty of yard space
• Your soils are uncontaminated, productive and/or easy to manage

Permanent raised beds are fitting if:

• You have limited yard space
• Your soil contains contaminants (such as lead)
• Your soil is difficult to work with
  • High clay, low fertility, poorly drained, compacted, etc.
• You have physical limitations that make bending over a challenge
• You enjoy the look of a permanent bed!

If temporary beds seem appropriate for you, congratulations! You are one of the lucky few with access to space and manageable soil. For most people, especially city-dwellers, permanent raised beds are a perfect solution to challenges posed by many urban soils.

You can find more information on permanent raised beds here. Information about urban soils can be found here, and guidance on testing for and/or dealing with soil contaminants can be found here.

Healthy soil is dark, well-drained and loose. Source: SSSA files

Once you’ve established your perfect garden, it is important that you maintain the health of your garden’s 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 loose granular structure, well-drained but moist soil, and a relatively dark soil color (influenced by organic matter).

A few easy ways to maintain soil health in your raised beds include the following:

1. 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.
2. 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 dealing with contaminated soils, please first seek professional guidance before developing a permanent raised bed.
3. Amend your soil with organic matter every spring. Organic matter is a great source of slow-released plant nutrients. It encourages structure development 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.
4. Cover your soil, especially during the off-season! Naked soil is vulnerable to wind and water erosion. Both processes effect soils in different ways, though all lead to soil and organic matter loss, reduced water infiltration, and structural loss. Cover crops are a great solution, as they also provide additional nutrients to your soil. They can also be tilled into the garden bed before planting 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 tips that will reap great rewards. Good luck, and happy gardening!

Answered by Mary Tiedeman, soil scientist

To receive notices about future blogs, be sure to subscribe to Soils Matter by clicking on the Follow button on the upper right! Explore more on our webpage About Soils. There you will find more information about Soil Basics, Community Gardens, Green Infrastructure, Green Roofs, Soil Contaminants, materials for Teachers and more.