DIY raised garden bed: build a simple bed in an afternoon

A DIY raised garden bed is one of the simplest builds in the garden, and a basic 4 by 8 foot (1.2 by 2.4 m) bed goes together in an afternoon with four boards, some screws, and a drill. You cut the boards to length, screw the corners together to form a rectangle, level the frame in a sunny spot, lay cardboard over the grass, and fill it with a mix of topsoil and compost. There is no bottom to build and no complicated joinery. If you can drive a screw, you can build a raised bed.

My first bed was four cedar boards from the local yard, joined at the corners with deck screws, set against the south wall of the house and filled with bulk topsoil and compost. It took me an afternoon, including a trip back to the store for longer screws, and that bed grew vegetables for nearly a decade before the wood finally gave out. You do not need plans, brackets, or fancy hardware to build a bed that lasts. A rectangle of rot-resistant wood filled with good soil is all it is.

Choose the wood

The wood you choose sets how long the bed lasts and how much it costs. Naturally rot-resistant woods like cedar (Thuja spp.) and redwood (Sequoia sempervirens) last around 10 years or more without any treatment, because they resist the moisture and rot that destroy a wooden bed sitting in damp soil. They cost more up front but save you rebuilding for years.

Untreated pine (Pinus spp.) or fir (Abies spp.) is cheaper and easy to find, but it rots in 3 to 5 years in contact with wet soil, so you trade a lower cost now for rebuilding sooner. It is a reasonable choice for a first bed if budget is tight, with the understanding that you will replace it before long.

Pressure-treated lumber lasts a long time. The American Wood Protection Association recommends labeled UC4A or higher treated lumber for horticultural uses, and Clemson HGIC 1257 notes that modern treated wood is considered safe for vegetable beds by many gardeners, though some prefer to avoid it for food crops. Old pressure-treated wood from before 2003 contained chromated copper arsenate (CCA) and should not be used for growing food. If you want to avoid the question entirely, untreated cedar is the simplest safe choice that still lasts.

Pick the size and depth

A 4 by 8 foot (1.2 by 2.4 m) bed is a good standard size. Four feet (1.2 m) wide lets you reach the center from either side without stepping on the soil, and 8 feet (2.4 m) long suits the standard length of lumber, so you waste no wood. Adjust the length to your space and the boards you can get, but keep the width at 4 feet (1.2 m) or less. Clemson HGIC recommends 3 to 4 feet (0.9 to 1.2 m) wide for exactly this reason, so the gardener can reach the center without stepping into the bed.

For depth, 10 to 12 inches (25 to 30 cm) suits most vegetables, and a single 2 by 10 or 2 by 12 board on edge gives you that. Standard nominal lumber comes in actual widths of 9.25 inches (2 by 10) or 11.25 inches (2 by 12), so one board on edge makes a bed that depth in a single course. For root crops or a bed on hard ground, stack two boards for more depth, or simply rely on the roots growing into the soil below, since a raised bed sits open to the ground.

What you need

Gather your materials and a few tools before you start, so you are not stopping mid-build for a second trip to the store. For a 4 by 8 foot (1.2 by 2.4 m) bed you need two boards 8 feet (2.4 m) long for the long sides and two boards 4 feet (1.2 m) long for the ends, or one long board cut down to those lengths.

You also need exterior or deck screws at least 2.5 to 3 inches (6 to 7.5 cm) long in stainless steel or hot-dip galvanized coating, and optionally four 4 by 4 inch (10 by 10 cm) corner posts or metal brackets to reinforce the joints. For tools, a drill or driver, a drill bit for pilot holes, a saw if you are cutting the boards yourself, a 2-foot (60 cm) or longer level, and a tape measure cover everything. Many lumberyards will cut the boards to length for you, which saves you the saw and gives you cleaner cuts.

Level the frame properly

The step people skip and later regret is leveling the frame. A bed that sits on sloping or uneven ground holds water unevenly, drains to one corner, and looks crooked. Spend the few extra minutes to get the top edges level before you fill it.

Set the assembled frame in place and rest a level across the top edges in both directions. If one side sits high, dig the soil down under that side until the frame sits level. If one side sits low, pack soil under it to raise it. Work around the frame until the top edges are level all the way around. On a noticeable slope, you may need to dig the uphill side into the ground and build the downhill side up so the soil inside sits level rather than running to one end.

A small slope is fine if you cannot fully level the frame. Compensate by burying the uphill edge an inch or two into the slope and letting the downhill edge stand a bit taller, so the soil surface inside sits flat. Water will then soak in evenly rather than running down to the low corner.

Leave the bottom open

A raised bed does not need a bottom. It sits open to the ground below, which lets roots grow down into the soil and lets water drain out the bottom. A solid bottom would trap water and limit root depth, so leave it open.

Before filling, lay cardboard or several sheets of newspaper across the ground inside the frame to smother the grass and weeds underneath. Overlap the edges so no gaps let weeds push through, and wet the cardboard down to hold it in place and start it breaking down. The grass and weeds die off under the cardboard, which then rots away and feeds the soil. You do not need to dig out the sod first, since the cardboard does that work for you.

The only time you need a bottom is for a bed on a hard surface like a patio, deck, or balcony, where there is no soil below to drain into. In that case, build a bottom with drainage holes and use a deeper bed, since the roots cannot grow into the ground.

Fill and plant

Once the frame is level and the cardboard is down, fill the bed with a good soil mix. About half topsoil, a third compost, and the rest an aeration material like coarse sand or bark makes a mix that holds moisture, drains well, and grows good vegetables. Clemson HGIC 1257 recommends compost at 10 to 20 percent of the total bed volume for the same reason. Order the soil in bulk by the cubic yard for a large bed, which costs far less than bags.

A 4 by 8 foot (1.2 by 2.4 m) bed 12 inches (30 cm) deep needs about 32 cubic feet, or roughly 1.2 cubic yards (about 907 L). Fill the bed, water it thoroughly to settle the soil, and top up any low spots once it has settled, since fresh soil sinks after the first soaking. For a deep bed, you can save on fill by putting logs, branches, or wood chips in the bottom few inches before adding the soil.

Then plant. The bed is ready to grow vegetables the day you fill it, with no waiting for soil to improve. Start with easy crops, water steadily, and top the bed with an inch (2.5 cm) of compost each spring to keep the soil rich. Built from good wood, filled with good soil, and topped up each year, a DIY raised garden bed grows vegetables for years from one afternoon’s work.

Bed material options at a glance

Sources: Clemson Cooperative Extension, HGIC 1257 Raised Beds; American Wood Protection Association, AWPA Use Category System.