Raised Beds

Raised beds are a common gardening practice that raises the elevation of the soil surface above the surrounding soil and increases the volume of soil being used to grow plants. With heights ranging from a few inches to several feet and a diversity of shapes, raised beds allow for flexible designs based on the needs, abilities, and wants of the user.

Raised beds provide a number of benefits to plants and practitioners:

• Extended growing season
• Improved drainage
• Ease of soil management
• Accessibility to growing spaces for a variety of users
• Contaminant mitigation and physical separation from underlying soil
• Attractive element of garden design

Raised beds can be beneficial in a number of situations. Soil in urban areas is often contaminated with heavy metals, toxic man-made chemicals, and other problematic materials. Raised beds provide a way to grow plants in uncontaminated soil and avoid issues related to toxicity. Raised beds can also increase soil drainage, which is useful in areas with heavily compacted, poorly drained, or flooded soil. As raised beds can increase soil temperature, they are useful in cooler areas and can be used to extend the growing season.

It is important to note that in some cases, raised beds are not ideal, namely in windy, dry, or warm areas due to increased soil temperature and drainage and less protection against wind. Be conscious of your climate and environment when considering raised beds.

There are two main types of raised beds: framed and unframed. Framed raised beds are also called structural, permanent, enclosed, or walled raised beds. Unframed raised beds are also called mounded, hilled, temporary, or frameless raised beds. We will use the terms “framed” and “unframed.” Note that “raised bed” is often used to refer only to framed raised beds. While the main benefits of framed and unframed raised beds are the same, there are benefits and downsides to both types. It is important to understand these in order to choose which raised bed is the best for your lifestyle. The chart below shares an overview of the pros and cons of each type of bed, and more information can be found in the following sections on this page.

The most important benefit from raised beds is the ability to provide an improved plant growth environment. This is the result of multiple properties created by the increased height and the ability to easily manage the soil in the bed.

Framed raised beds can be aesthetically pleasing since they are more contained and variable in design than unframed raised beds. Framed beds are more accessible than unframed beds as they can be built up to the needed height. They can be designed to be larger and use space more efficiently, and, if cared for correctly, framed beds can last a long time. They are convenient if you have limited space, sloped land, are wanting to build a hoop house or mini-greenhouse, or would like to cover your crops. Weed and pest management is easier with framed beds, in part due to the use of landscape fabric or another physical barrier over the soil below. In the case of contaminated, compacted, or inappropriately textured soil, this can provide another layer of protection to prevent soil mixing as well.

• Improved drainage. With the elevated height, the soil is less likely to become saturated with water during wet periods. The moisture may arrive due to high water tables or large storm events, but by simply raising the elevation, the raised bed can avoid the high water table or allow the rain water to drain more freely from the raised bed’s soil.
• Extended growing season. With their elevated position, soils in raised beds tend to warm up faster in the spring. This is due to the soils being drier and therefor more easily warmed by sunlight and spring rains. Warmer soils allows for plants (seed germination, tender annuals and perennials) to get an earlier start in the spring and thus extending the growing period to earlier in the season. This can be countered by earlier cooling in the fall, which would shorten the growing season, but with smart management (see below) this can be overcome.
• Increased rooting volume. With increased soil depth comes increased rooting volume. While not always needed, with proper management healthy and productive soil environments can be created to overcome agronomic limitation from native soil. Raised beds are often used to manage for wet native soils, impervious barriers, poor water holding capacity, inadequate nutrients, inappropriate pH and/or contaminated soils.
• Prevent erosion. When the soil is held in a structure, the raised bed will act to prevent that soil from being lost by wind or water movement. Often used on sloping land to divert or slow water, these structures can also protect the surrounding landscape from soil erosion.
• Preventing contaminant. When dealing with contaminated soil two effective strategies are to create a barrier between or distance from the contamination and the growing media. Depending on the height of the structure, raised beds can be effective for both of these strategies. For these benefits to work, clean soil must be placed in the bed and the added soil must be deep enough to prevent roots from reaching into the contaminated soil below. It should be noted that a physical barrier, such as landscape fabric, will also help in preventing upward mixing of contaminated material into the clean soil as well as prevent downward growth of plant roots into contaminated soil.
• Ease of access. The increased height of raised beds provides access to plants and soil for gardeners with limited mobility. This raised elevation also helps in a number of other ways: easier identification of soil and plant issues that may be hidden under plants, easier harvest and weeding, and access to water at the base of the plant, which can help prevent disease.

Notes about downsides:

Framed raised beds require some degree of craftmanship, especially if you desire a more complex design. They require extensive planning to figure out needed equipment and materials, proper dimensions, total expenses, and placement as they are more permanent than unframed raised beds. Framing material must also be considered carefully as many materials are not appropriate for building raised beds. Chemicals from the material can leach into the soil, causing issues of contamination even if you are using uncontaminated soil. Oftentimes, rot resistant hardwood, concrete or landscaping pavers/blocks, galvanized metal, stackable bricks or rocks, and food grade plastics are acceptable, but pressure-treated wood, used tires, cinder blocks, and materials of unknown origin are unacceptable. Materials containing known contaminants are also unacceptable. Regarding soil care, it can be more difficult to till or incorporate compost and other organic matter into the soil.

The main benefits of unframed raised beds are their cost efficacy and minimal equipment, material, and skill requirement. All that is needed is uncontaminated soil from your yard or a verified seller. Since unframed beds do not require any building materials, it is easy to avoid any potential toxicity from framing materials. Unframed beds can be easily incorporated into your growing area, including already existing landscapes and gardens as you have a control over their shape and size. Your growing area can be further expanded by growing on the inclines of the beds. Deep trenches can easily be built between each bed, which can be beneficial for plants that are easily waterlogged. Regarding soil care, compost and other organic matter can easily be incorporated into the soil to increase soil fertility.

At their most basic, raised beds are a simple hill of soil in a desired location. These are a type of unframed beds. Often structures are built to hold the soil material at increased heights, prevent erosion of gathered soil, or for design reasons. These are framed beds. The images at the top of the page show this distinction.

Constructing Framed Beds

Framed raised beds are often built with wood-based materials, but can be constructed from any material that will be able to maintain its shape and strength in the outdoors against the strain of soil pressure and weather.

Materials to use:

• Rot resistant woods
• Food grade plastics (high density polyethylene, HDPE #4)
• Concrete blocks
• Rocks or stones
• Bricks
• Galvanized sheet metal

Materials to avoid:

• Pressure-treated (PT) wood
• Used tires
• Cinder blocks
• Plastic wood composites

Filling Beds

As with all soils, take care to build healthy soil environments inside your raised beds to create productive plant environments and avoid possible contaminants. Common choices of materials to fill your beds include:

• Soil from surrounding areas
• Top soils and sands from landscape suppliers
• Yard waste and manures
• Composts

Food scraps are also often added, but be careful to bury the material to avoid any pests and encourage decomposition. Avoid yard waste or other plant materials that may have pesticides or salts.

Both framed and unframed raised beds have their benefits and downsides, and the type you pick depends on your preferences and lifestyle. Here are some things to consider:

• Keep in mind that many of the benefits of raised beds are only observed when you use healthy, uncontaminated soil and add enough compost/organic matter to increase soil fertility, improve pH and water infiltration, increase crop yield, and reduce weeds.
• Only fertilize when needed to avoid issues of leaching or surface water eutrophication due to storm water.
• If contaminated soil is a major issue, consider growing ornamental or fruiting crops instead of roots, tubers, or leafy crops.
• Wash all fruits, leaves, and other edible parts carefully before consumption, and avoid unnecessary contact with the soil.
• Pay careful attention to watering your raised beds as they may dry out faster due to increased drainage. Be aware of your planting zone and choose plants accordingly.
• Build your raised beds away from traffic and driveway and keep any beds that are closer to traffic low to the ground to minimize accidents.
• Keep in mind that in some areas, raised beds must be framed regardless of your preference. Check to see if there are any requirements or recommendations for building raised beds, or for gardening or urban agriculture in general, in your area.

How to build framed and unframed raised beds:

University of Minnesota –Raised Bed Gardens

Framed bed materials:

University of Georgia –Raised Bed Materials

Soil contaminants:

Soil Science Society of America –Soil Contaminants

Healthy Soils, Healthy Communities

Vegetable root depth:

University of California –Vegetable Root Depth Chart

Unframed Raised Bed Construction video:

Instant Raised Garden Beds By Flipping Sod

How To Make An Unframed Raised Bed

Mounded Raised Bed

Urban Gardening Resources

Cornell Small Farms Program–Guide to Urban Farming in New York State

EPA–Growing Gardens in Urban Soil

NYC parks GreenThum Gardeners’ Handbook (2023)

Articles & News About Raised Beds:

Long, C. (2013, May 1). How to Make Cheap Garden Beds – You’ll have your best garden ever if you create permanent garden beds — whether they’re raised beds, at ground level, framed or unframed. Mother Earth News (USA). Available from NewsBank: America’s News Magazines: https://infoweb-newsbank-com.proxy.library.cornell.edu/apps/news/document-view?p=AMNP&docref=news/149176E4AD6ECC60.

Miernicki, E. A., Lovell, S. T., & Wortman, S. E. (2018). Raised beds for vegetable production in urban agriculture. Urban Agriculture & Regional Food Systems, 3(1), 1-10.

“Raised beds take gardening to higher level; Urban Growth.” Toronto Star [Toronto, Ontario], 10 Sept. 2016, p. H2. Gale OneFile: News, link.gale.com/apps/doc/A462985742/STND?u=cornell&sid=ebsco&xid=9d1494ad.