Raised beds are a great solution for many gardeners, and for many reasons.
In areas where the soil is poor, a raised bed allows you to skip all the double-digging, weeding and amending in the effort to get a healthy environment for your garden. Simply add the ideal mixture of garden soil and compost to the bed, and it’s pretty much ready to plant.
Raised beds are also easier to work in, since you won’t have to bend or crouch as far. In fact, some taller raised beds can be reached while standing or from a wheelchair.
Even though a raised bed may offer less square footage than a garden plot, it can be more productive because it’s easier to access the entire planting area and do companion planting that utilizes every foot of the bed. You’re better able to keep on top of weeds, too.
A further benefit of compact raised beds is that they can be covered during cold weather, which allows you to plant earlier in the season. During summer’s heat, you can also use shade cloth on your row covers to protect your plants from sunburn.
Here are some basic considerations on building a raised garden bed:
What size should raised beds be?
The general rule is that raised beds should be no wider than you can reach across. So as long as you can easily reach a foot-and-a-half or two, you may make your beds 3-4 feet wide, as long as you can get around all sides.
The length of the beds doesn’t really matter. Some gardeners create beds the entire length of a fence line; others use the beds to construct a formal garden look. Orient the beds to suit your landscape; the sun will reach the plants which ever way the beds face. Just make sure the bed location gets the required amount of sun for the plants you’ll be using.
How many gardeners will be working there? You may wish to provide space especially for children to use, or in a community garden, each gardener will want their own bed to tend.
Raised bed design
Raised beds can be constructed from a variety of materials, including wood or composite lumber, stone or concrete blocks, or by simply berming the soil to raise it above ground level.
As the University of California says in “Selecting Lumber and Lumber Substitutes for Outdoor Uses”, there are a number of materials that make good raised gardens. These include untreated woods with natural resistance to rot, such as redwood, mahogany, cedar and others.
There are many designs for raised beds, from the purely functional to architectural masterpieces. But for most of us, a simple design with solid, clean lines is perfect.
Here’s the simplest design I’ve seen yet:
Choose boards that are 2 inches thick and 12 inches wide. Purchase them the length you’d like your bed to be, or arrange to cut them down. For instance, for an 8-foot-long bed that’s 4 feet wide, you need three 8-foot boards. Use two for the sides and cut one in half to use for the ends.
Purchase one 4×4 post and cut it into four 16-inch-long pieces. These will be the corner posts. Nail or screw the side rails to the top of the post, leaving a flat area on the top of each corner.
Put the bed frame in place on your desired location, digging the post extensions into the soil to anchor it. (Like it’s going to move once it’s filled with soil anyway!)
And voila! Your raised bed is ready to be prepared for planting.
If you’d like to see someone building a raised bed, this video class from Craftsy will show you the materials you’ll need, how to cut and construct your bed, how to fill it with soil, create a simple irrigation system, and how to cover it. I like these classes because you can watch them at your convenience and your access never expires. (I do earn a small commission on your purchase of Craftsy classes to help support this site.)
But first, a word on using pressure-treated lumber for raised beds:
Is pressure-treated wood safe to use?
At first glance, it may seem that pressure-treated wood is the best choice for raised beds, which will regularly be subjected to water and moisture. But some gardeners, especially those with small children, have been concerned about using chemical-treated wood around plants used for food.
Before 2004, lumber was commonly treated with Chromated Copper Arsenate, or CCA, which contained arsenic, chromium and copper that could leach from the wood as it weathered.
While the Environmental Protection Agency concluded that raised beds constructed with CCA-treated lumber did not present a health hazard, due to safety concerns about decks and playgrounds made from such wood, CCA is no longer used to treat lumber for residential use.
If you do happen to have lumber treated with CCA that you’d like to use for your raised bed, simply line the sides of the bed with plastic to avoid contact with the soil if you‘re concerned about leaching. This effect is greatest in the soil immediately adjacent to the lumber. The amount of chemicals that leach from the wood decreases over time.
As I planned to use pressure-treated lumber left over from a recent fencing project, I checked to make sure it was safe to use near vegetables. This Severe Weather brand, purchased from Lowes, is labeled “Ground Contact General Use,” and it’s treated with ACQ-A: Alkaline Copper Quaternary (ACQ), with copper Azole (CA).
The active ingredient in ACQ is copper, which humans actually need in their diet. Copper poisoning is very rare, and the amount your vegetables could possibly absorb by using copper-treated wood is negligible. The copper keeps insects at bay, and the fungicide prevents soil fungus from attacking the wood.
This very technical study of ACQ-treated wood concludes it is safe for children to play on.
If you still have any concerns about using ACQ-treated lumber, simply line the bed with plastic. That will keep the wood even drier, prolonging its life. You can also top the sides of the bed with untreated lumber, which makes a nice place to sit while you garden.
Prepare the ground and filling with soil
Before you can fill the bed with soil, you’ll need to keep existing grass and weeds from invading your nice, fresh planter.
No, don’t use weed killer!
You can always dig down to remove top layer of grass from the area, but you can also make it easier on your back by covering the area with newspaper, cardboard or landscape fabric to kill off the grass and weeds underneath.
Fill the bed with a good mixture of 2 parts garden soil to 1 part compost, with a shovelful of fertilizer mixed in.
If you have the foresight to build your planter in fall, you can layer organic matter from your compost pile on top of the paper or cardboard. Alternate “browns” and “greens” until the mixture is about two-thirds of the way up the sides of your bed.
Then top the layers with a few inches of garden soil. Add a bit more garden mix in the spring, and you’re ready to plant.
Remember, if you need more help, refer to Karen and Andy Chapman’s “Building a Raised Bed Garden” from our Craftsy affiliate.