Community News

Gardening 101: Container and Raised Bed Gardening

Part 1 – Raised Bed Gardens

With gardening season quickly approaching, Gakwi:yo:h Farms is providing helpful information pertaining to these two methods of gardening

Submitted by Mike Snyder, Gakwi:yo:h Farms Director | Reprinted from GrowPittsburgh.org

How-To: Building Raised Beds. In an urban setting, raised beds gardens are used to create “islands” of fertile, clean soil in areas where none exists. If they are carefully planned and built, raised beds will provide garden space for many years.

Why Raised Beds? There are many reasons to build a raised bed garden! If any of the following describe your garden space, raised beds may be a good fit for you.

Lack of Good Soils – Raised beds can be built on asphalt, or in areas with thin soil or heavy metal contamination. *Please note that we recommend soil testing for any type of garden site. If heavy metals exist, a raised bed may be built on top of a heavy barrier that keeps the contaminated and safe soil from mixing.

Poor Drainage – Raised beds lift the growing area above ground level. This can make a big difference for waterlogged areas that could otherwise drown plant roots.

Accessibility Needs – Raised beds can be built to any height, which makes them a great fit for gardeners who are unable to bend to ground level.

Many Visitors– Because raised beds have clearly defined edges, they work well in spaces with lots of foot traffic. Raised beds protect the garden areas from being trampled and compacted. Raised beds are especially well suited for children’s gardens!

Raised beds also look tidy, which can be important in highly visible locations. They extend the season, as they warm up more quickly than the ground. Because the soil inside is lighter and less compacted than the surrounding land, they can be easier to plant, regardless of the weather.

There are a few drawbacks with raised beds as well. The materials can be expensive, and it’s labor intensive to construct and prepare them the first season. However, once raised beds are built, they require very little money and maintenance.

How to Build Raised Beds

Location– Raised beds work best on flat sites. If there is a gentle slope, dig into the hill when installing the raised bed so the bed sits level. This will help prevent soil from eroding from the bed when it rains.

Bed Dimensions – We recommend beds 3′ wide or less, to make the whole bed easily reachable. Lumber should be at least 1″ thickness and 8″ height. Alternatively, you can stack two boards to make a deeper bed.

Walkways – Consider the dimensions of walkways, too. You’ll want to be able to move easily and possibly maneuver larger items like a wheelbarrow or mower between beds.

Decide whether to grow a groundcover in the walkways and mow it regularly, or put down mulch.

For the Frame – A variety of materials can be used to build the raised bed structure. A bed made out of untreated lumber is easiest to install. We recommend cedar, hemlock, larch (tamarack), or black locust. Do not use treated lumber for beds or trellises you will grow food in/on, as this wood is treated with chemicals that have not been approved for food gardening. Please see the chart for more information on each type of lumber (see next page). Clean bricks, landscaping blocks, Belgian blocks, or rocks could also be used for the edges of the bed.

If you plan to stack two boards to create a deep enough bed, secure the boards together with a “cleat” – a short piece of 1″x4″ or 2″x4.” (Please see diagram.)

Bed corners are the first to show signs of wear and tear. Building them well can add years of life to the bed. Plan to order and use 2″x2″ or 4″x4″ posts to secure the interior corners of the bed. (Please see diagram.)

Soil – For filling the beds, we recommend a topsoil: compost ratio in the range of 70:30 to 50:50. You can purchase bags of topsoil and compost for a small bed, or find a local nursery or compost supplier to deliver a larger amount of materials. For beds that are 18″ deep or more, treat the raised bed as a large container, and avoid topsoil, which can be too heavy. For these deep, container-like beds, we mix 5-gallon buckets of materials in the following ratio: 2 buckets compost, ½ bucket vermiculite, ¼ bucket peat, 1/8 bucket sand.

Hardware – Choose galvanized or zinc plated screws meant for outdoor use. Lag bolts, lag screws, or deck screws will work. Pre-drill holes, as the lumber could be very dense or may split easily. Metal corner braces are not necessary but can help with construction.

Liner – A liner is not needed, unless there is no soil beneath the bed or the soil underneath the bed is contaminated. Liners are commercially available and keep the soil in the raised bed from seeping out the side of the frame, or mixing with the soil beneath the raised bed. After the bed is built and placed in its final location, lay down cardboard if you are not using a commercial liner. The cardboard will smother weeds or turf and will eventually break down.

Choosing Lumber for Raised Beds

Lumber for Raised Beds– Choosing the right type of wood makes a big difference for raised bed gardens! Some wood rots easily and other types will last for years.

Ordering Lumber – All types of lumber are typically available in 8-foot lengths. Other available sizes generally include: 10′, 12′, 16′ and 24′. There are three dimensions to consider:

  1. Thickness of board. 1-2″ depending on the strength of the type of lumber. (Please note that lumber sold as 2″x4″ is actually 1.75″x3.75″ or less.)
  2. Width (or height) of board. It may be possible to find lumber that is 12″ wide, to build a bed 12″ high. More likely you will need twice the number of boards at half the width/height (for example, 2, 6″ boards, stacked).
  3. Length of board. Length is usually measured in “board feet” or “linear feet”. This is the total length of lumber needed. For example, a 3’x12′ bed would require a total 30 board feet of lumber (two walls 3′ long plus two walls 12′ long). Suppliers can cut lumber to length, for a nominal fee. Plan to order extra wood for corner posts (2×2″ or 2×4″) and/or 1×4″ or 2×4″ cleats to join narrow boards.

Online Resources:

^^ Citation Grow Pittsburgh http://www.growpittsburgh.org/wp-content/uploads/General-Info-Lumber-for-Raised-Beds-for-web.pdf

University of Maryland Extension – Container gardening resources – https://extension.umd.edu/hgic/topics/container-gardening.

The April 24, 2020 edition will feature CONTAINER GARDENING (Part 2) information and the comparisons between raised bed vs. in-ground gardens.