What you need to build a raised bed

A raised bed is a wooden or composite box that sits on top of your existing ground. 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 soil to fill it. Most people build beds 4 feet long by 2 or 3 feet wide by 10 to 12 inches deep, though you can adjust these dimensions to fit your space.

The most common material is untreated cedar or composite lumber, because both resist rot without chemicals. Pressure-treated wood is cheaper but contains preservatives that can leach into soil over time—avoid it for vegetable gardens. Composite boards cost more upfront but last 15 to 20 years instead of 5 to 10.

You will also need a drill with a screwdriver bit, a level, a tape measure, and a saw if you are cutting boards to length. If you buy pre-cut boards from a garden center, you can skip the saw. A pair of work gloves and safety glasses are worth having.

Key Takeaways

  • Raised beds are built from untreated cedar or composite boards fastened at the corners with screws or brackets, then filled with soil and planted.
  • A standard bed is 4 feet by 2 feet by 10 inches deep, but you can adjust the size to fit your yard and reach comfortably from the sides.
  • The bed sits directly on grass or bare ground—you do not need to remove sod first, though cardboard under the bed slows weed growth.
  • Filling a 4-by-2-foot bed requires about 8 cubic feet of soil, which is roughly one cubic yard or three 40-pound bags per 4 inches of depth.
  • You can plant when ready after filling, but beds settle over the first few weeks, so you may need to add more soil later.

Choosing a location and preparing the ground

Place your bed where it will get at least 6 hours of direct sun per day for vegetables, or 3 to 4 hours for leafy greens. Avoid spots under trees or next to buildings that cast long shadows. Check that water drains away from the location after rain—if water pools there, the bed will stay waterlogged.

You do not have to remove the grass or sod underneath. The bed will kill the grass over time as it blocks sunlight. If you want to speed this up, lay cardboard or several layers of newspaper under the bed before filling it. This also creates a barrier that slows weeds from growing up into the bed from below. Wet the cardboard so it stays in place and breaks down faster.

Level the ground as much as you can before building. If the ground is very uneven, the bed will sit unevenly and water will pool on one side. You do not need a perfectly flat surface—just remove large rocks and high spots so the frame sits mostly level.

Assembling the frame

Cut your boards to length if needed. For a 4-by-2-foot bed, you need two 4-foot boards and two 2-foot boards. Lay them out on the ground in a rectangle to check the fit before fastening anything.

Fasten the corners using one of two methods. The first is corner brackets: metal L-shaped brackets that bolt or screw to the inside of two boards where they meet. This is the easiest method for beginners because you do not have to cut angles or worry about boards splitting. Drill pilot holes (small starter holes) first, then drive the screws through the bracket into both boards.

The second method is wood screws driven directly through one board into the end of the other. Use 3-inch exterior screws, at least two per corner. Drill a pilot hole in the board you are screwing through, then drive the screw at a slight angle so it bites into the end grain of the other board. This method is faster once you get the hang of it, but boards can split if you do not use pilot holes.

Check that the frame is square by measuring corner to corner—both diagonals should be the same length. Use a level to check that the top edges are roughly level. Small gaps are fine; the soil will settle and fill them.

Filling the bed with soil

A 4-by-2-foot bed that is 10 inches deep holds about 6.7 cubic feet of soil. A 4-by-2-foot bed that is 12 inches deep holds about 8 cubic feet. One cubic yard of soil (the standard bag size at garden centers) is 27 cubic feet, so one yard fills roughly three standard beds.

You have three options for what to fill it with. The cheapest is topsoil from a landscape supplier, which is usually just the top layer of excavated soil. It is heavy, often compacted, and may contain weed seeds. The middle option is garden soil or potting mix from a garden center, which is lighter and has some compost mixed in. The best option for vegetables is a raised bed mix (sometimes called "garden in a bag"), which is a blend of topsoil, compost, and peat moss or coconut coir designed to drain well and hold nutrients.

Fill the bed to the top, then water it thoroughly. The soil will settle over the next week or two, dropping 1 to 3 inches depending on how compacted it was. You may need to add more soil after the first watering. Do not pack the soil down—let it settle on its own.

Preventing pests and extending the season

Raised beds are easier to protect from pests than in-ground gardens because you can add barriers. A hardware cloth (metal mesh with half-inch holes) laid on the ground under the bed stops burrowing rodents and moles. Staple it to the bottom of the frame so it does not shift.

For above-ground pests, a straightforward row cover (lightweight fabric) draped over the bed and held down with stakes or soil keeps insects off young plants. Remove it once plants flower and need pollination. For longer seasons, a cold frame (a wooden box with a clear plastic or glass lid) placed over the bed traps heat in spring and fall, extending your growing season by several weeks on each end.

Raised beds also warm up faster in spring because the soil is exposed to sun on all sides, not just the top. This means you can plant earlier than you could in the ground.

Maintaining the bed year after year

Each year, add 1 to 2 inches of compost to the top of the bed before planting. This replaces nutrients that plants took out and improves the soil structure. You do not have to dig it in—just spread it on top and let earthworms and microbes work it down.

Check the frame every spring for rot or loose fasteners. Cedar and composite boards last much longer than pressure-treated wood, but even they eventually need replacing. If a board starts to rot, you can replace just that one board without rebuilding the whole bed—unbolt or unscrew the corners and slide the old board out.

Drain the bed in late fall if you live in a cold climate. Soil that stays waterlogged over winter can freeze and thaw repeatedly, which breaks down the structure and kills beneficial microbes. Let the bed dry out naturally in fall, or drill a small drainage hole in one corner if water pools there.

Common mistakes to avoid

The most common mistake is building the bed too deep. A 12-inch bed is plenty for most vegetables—roots do not need more than that. Deeper beds use more soil and cost more without any benefit. The exception is root vegetables like carrots and parsnips, which need 12 to 18 inches.

The second mistake is using pressure-treated lumber or old railroad ties. Both contain chemicals that can leach into soil. Cedar, composite, or untreated pine are all safe choices. If you already have a bed made from pressure-treated wood, you can still use it for ornamental plants or flowers, just not for vegetables you plan to eat.

The third mistake is filling the bed with only topsoil. Topsoil alone compacts over time and does not drain well. Mix it with compost or use a raised bed mix instead. The extra cost is worth it because the bed will drain better and hold nutrients longer.

Frequently Asked Questions

Can I build a raised bed on top of concrete or pavement?

Yes. Drill drainage holes in the bottom of the frame or use a landscape fabric liner with holes cut in it so water can drain. Without drainage, roots will rot. You will also need to water more often because the concrete does not absorb moisture the way soil does.

How long does it take to build a raised bed?

Assembly takes 30 minutes to an hour if you have the tools and materials ready. Filling it with soil takes another 30 to 45 minutes depending on how many bags you need to carry. You can plant the same day you fill it.

Do I need to line the inside of the bed with plastic or landscape fabric?

No. Landscape fabric under the bed stops weeds from below, but you do not need it inside the frame. It can trap water and cause rot. If you are concerned about chemicals from old wood, use a fabric liner, but it is not necessary with cedar or composite boards.

What size raised bed should I build?

A 4-by-2-foot bed is the standard because you can reach the center from either side without stepping into it. If you have limited space, a 4-by-1-foot bed works fine. Avoid beds wider than 3 feet because you will have trouble reaching the middle without stepping on the soil and compacting it.

Can I build a raised bed in the shade?

You can, but only for shade-tolerant plants like lettuce, spinach, kale, and herbs. Most vegetables need at least 6 hours of direct sun. If your yard is mostly shaded, consider a smaller bed in the sunniest spot you have, or grow shade plants instead.