What You Need to Build a Raised Bed
A raised garden bed is a wooden or composite box you fill with soil and plant into. To build one, you need lumber (usually 2-by-10 or 2-by-12 boards), corner brackets or wood screws, a drill or screwdriver, a level, and a saw if you're cutting boards to length. Most people also add landscape fabric to the bottom to block weeds, and a corner post or L-bracket at each corner to hold the frame square.
The simplest design uses four boards screwed or bolted together at the corners. You can buy pre-cut kits that come with all pieces ready to assemble, or you can buy lumber from a hardware store and cut it yourself. Cedar and composite materials last longer than pine or spruce, but they cost more. Pine boards typically last five to seven years before rot sets in; cedar lasts ten to fifteen.
You do not need a foundation, but the ground should be relatively level. If your yard slopes, you can dig out the high side and build up the low side with soil, or you can accept that one side will sit higher than the other—plants don't mind.
Key Takeaways
- A basic raised bed uses four boards screwed together at the corners, with landscape fabric stapled to the bottom to block weeds.
- Cedar and composite lumber last longer than pine, but pine is cheaper and works fine for five to seven years.
- You can assemble a bed in an afternoon with a drill, a level, and a tape measure; no special tools or skills are required.
- The bed should sit on relatively level ground, and you fill it with topsoil or a soil mix rather than garden soil alone.
- A 4-by-8-foot bed is a common size that holds enough soil for most vegetables and is straightforward to reach across from either side.
Choosing Your Lumber and Size
The most common raised bed is 4 feet wide by 8 feet long by 10 or 12 inches tall. This size is wide enough to hold two rows of plants, long enough to be useful, and tall enough that you don't have to bend far to plant and weed. You can make it smaller (3 by 6 feet) if space is tight, or larger if you want more growing area.
For lumber, a 2-by-10 board is 9.5 inches tall when installed, and a 2-by-12 is 11.5 inches tall. Both work well. Cedar is the best choice if you plan to keep the bed for many years—it resists rot naturally. Composite lumber (made from wood fiber and plastic) lasts even longer and never rots, but it costs two to three times as much as cedar. Pressure-treated pine is cheaper and lasts longer than untreated pine, but some gardeners avoid it because of the chemicals used in the treatment. Untreated pine is the cheapest option and works fine if you're willing to replace boards every five to seven years.
Avoid railroad ties and old utility poles—they are often treated with creosote or other toxic substances that can leach into soil.
Assembling the Frame
Lay the four boards on the ground in a rectangle. At each corner, you have two choices: screw the boards together directly, or use a corner bracket or L-bracket to hold them square. Screwing boards together is simpler and cheaper. Brackets are stronger and make it easier to keep corners at 90 degrees.
If you're screwing boards together, drill a pilot hole first (a small hole that guides the screw and prevents the wood from splitting). Use 3-inch exterior-grade wood screws—at least two per corner, one near the top and one near the bottom. Tighten them firmly but don't over-tighten, which can strip the wood. If you're using brackets, follow the bracket's instructions; most bolt or screw to the inside of the corner.
Once the frame is assembled, place it where you want it and use a level to check that the top edges are even. If the ground is uneven, you can dig out the high spots or add soil under the low spots. The frame doesn't have to be perfectly level—a slight slope is fine—but if one corner is much higher than the others, water will run to the low side and plants on the high side may dry out faster.
Lining the Bottom and Filling with Soil
Before you fill the bed, line the bottom with landscape fabric to block weeds from growing up from the ground below. Landscape fabric is a thin, permeable material sold in rolls at garden centers. Lay it across the bottom of the bed and staple it to the inside of the frame with a staple gun. You don't need to cover every inch—just enough that weeds can't push through the gaps.
Fill the bed with a soil mix rather than garden soil alone. Garden soil is heavy and compacts over time. A better mix is about one-third compost, one-third topsoil, and one-third peat moss or coconut coir (a sustainable alternative to peat). You can also buy pre-made raised bed soil mixes at garden centers, though they cost more than mixing your own. A 4-by-8-foot bed that is 10 inches tall holds about 26 cubic feet of soil, which is roughly 1 cubic yard. A cubic yard of soil weighs about 1,500 pounds, so have it delivered if possible rather than carrying bags.
Fill the bed to within an inch or two of the top. The soil will settle over the first few weeks, so don't worry if it looks too full at first.
Positioning Your Bed for Sun and Water
Most vegetables need at least six hours of direct sun per day. Before you build, observe your yard throughout the day and note which spots get full sun and which are shaded by trees or buildings. Position the bed in a sunny spot if you're growing vegetables, or in partial shade if you're growing leafy greens or herbs that prefer cooler conditions.
Make sure the bed is close enough to a water source that you can reach it with a hose. If you have to carry water by hand, you'll be less likely to water consistently. Also avoid placing the bed directly under trees, where falling leaves will clog it and tree roots may grow into the soil.
If you're building on a slope, orient the bed so the long side runs across the slope rather than up and down it. This helps water distribute evenly.
Protecting Your Bed from Pests and Weather
Once the bed is filled and planted, you may want to add a cover to protect plants from birds, insects, or frost. A straightforward row cover (lightweight fabric that lets light and water through) can be draped over plants and held down with stakes or rocks. For more protection, you can build a frame over the bed and cover it with hardware cloth (a metal mesh that keeps out larger animals) or bird netting.
In winter, a raised bed drains faster than ground soil because water runs through the sides. If you live in a cold climate, you may need to water more often in late fall and early spring, or add mulch to the top to slow evaporation. In very hot climates, mulch also keeps soil cooler and reduces watering needs.
Check the frame each spring for signs of rot or damage. If boards are soft or crumbling, they need to be replaced. This is easier to do before the bed is full of soil, so plan ahead if you know a board is failing.
Frequently Asked Questions
Do I need to put anything under the landscape fabric?
No. Landscape fabric alone is enough to block most weeds. Some gardeners add cardboard under the fabric for extra protection, but it breaks down over time and doesn't add much benefit. If you're building on a lawn, you can skip the fabric and just lay cardboard directly on the grass—it will kill the grass underneath and eventually decompose.
Can I use treated wood in a vegetable garden?
Pressure-treated lumber sold today is safe for vegetable gardens. Older treated wood (before 2004) contained arsenic and should not be used. If you're unsure about the age of the wood, cedar or composite is a safer choice. Some gardeners prefer untreated wood for peace of mind, even though modern treated wood is considered safe.
How deep does a raised bed need to be?
Most vegetables grow well in 10 to 12 inches of soil. Root vegetables like carrots and parsnips need at least 12 inches. Shallow-rooted plants like lettuce and herbs can grow in 6 to 8 inches. If you're growing a mix, 10 inches is a good middle ground.
Can I build a raised bed on top of concrete or pavement?
Yes, but you'll need to add a bottom to the frame so soil doesn't fall through. Screw plywood to the underside of the boards, or line the bottom with landscape fabric and staple it very securely. Water will not drain as well, so you may need to drill drainage holes in the plywood or add a layer of gravel under the soil to prevent waterlogging.
What's the best time of year to build a raised bed?
Spring and fall are ideal because the weather is mild and you can plant right away. You can build in summer or winter, but you'll have to wait until the next growing season to plant. Building in fall gives the soil time to settle over winter, which is helpful.