What You Need to Build a Raised Bed

A raised garden bed is a wooden or composite box that sits on top of your existing ground. You fill it with soil and grow plants inside. Building one takes a weekend and requires only basic tools—a drill, a saw, and a level. Most people spend between $50 and $200 on materials, depending on the size and wood type you choose.

The simplest design is a rectangle made from four boards screwed together at the corners. You do not need a foundation, concrete, or special fasteners. The bed will settle slightly over the first year as the soil compacts, but that is normal and does not affect how it works.

Key Takeaways

  • Cedar or composite boards last 10 to 15 years; untreated pine lasts 3 to 5 years and costs less.
  • A 4-by-8-foot bed 12 inches deep is a standard size that holds about 32 cubic feet of soil and fits most yards.
  • Screw the corners together with 3-inch deck screws, using two screws per corner for strength.
  • Place the bed on level ground and check with a level before filling; uneven beds cause water to pool on one side.
  • You can build and fill a raised bed in one day, but let the soil settle for a week before planting.

Choosing Wood and Sizing Your Bed

Cedar is the most popular choice because it resists rot naturally and lasts 10 to 15 years without treatment. A 2-by-10-inch cedar board costs $3 to $6 per linear foot. Composite boards (plastic and wood fiber) cost more upfront—$8 to $12 per linear foot—but last 20 years and never rot. Untreated pine is the cheapest option at $1 to $3 per linear foot, but it breaks down in 3 to 5 years, especially in wet climates.

Do not use pressure-treated lumber from before 2004; older versions contained arsenic. Modern pressure-treated wood is safe, but many gardeners avoid it anyway because the chemicals can leach into soil over time.

A 4-by-8-foot bed 12 inches deep is the standard size. It holds about 32 cubic feet of soil, costs roughly $80 to $150 in cedar, and fits most residential yards. If you want something smaller, a 3-by-6-foot bed works well for herbs or a single crop. Avoid beds wider than 4 feet—you will not be able to reach the center without stepping into the soil.

Gathering Tools and Materials

For a 4-by-8-foot bed, you need two 8-foot boards and two 4-foot boards. If your lumber yard does not cut them, you can cut them yourself with a circular saw or ask the staff to make the cuts for free. You also need eight 3-inch exterior deck screws (two per corner), a drill with a screwdriver bit, a level, a tape measure, and a pencil.

Optional but helpful: work gloves, a square to check corners, and a rubber mallet to tap boards into place. If you are building on grass or weeds, a shovel helps clear the area first. Some people lay landscape fabric on the bottom to block weeds, though it is not required.

Building the Frame Step by Step

Start by laying out your two long boards and two short boards on a flat surface—your driveway or patio works fine. Arrange them in a rectangle so the short boards sit between the ends of the long boards. This is called a "butt joint" and is the easiest way to connect them.

Drill a pilot hole (a small hole that guides the screw) at each corner, about 1.5 inches from the edge. Use a drill bit slightly smaller than your screw diameter. Drilling first prevents the wood from splitting and makes the screw go in straight. Screw the first corner together with one 3-inch deck screw, then add a second screw below it. Repeat at all four corners.

Check that the frame is square by measuring diagonally from corner to corner. Both measurements should be equal—if they are not, the frame is racked (twisted). Tap the corners gently with a rubber mallet until the diagonals match. This step matters because a racked frame will not sit flat on the ground.

Positioning and Leveling Your Bed

Choose a spot that gets at least 6 hours of direct sun per day. Clear away grass, weeds, and large rocks. You do not need to dig down or remove topsoil—the raised bed sits on top of whatever is there.

Set the frame in place and use a level to check all four sides. Place the level along the length of each board and note where it is high or low. If one corner is high, you can dig out soil underneath or add soil on the opposite side. Most people accept a slight slope (less than 1 inch over 8 feet) rather than spend time leveling perfectly. Water will still drain, and plants will still grow.

Once the frame is level enough, you can add a landscape fabric barrier on the bottom if you want to block perennial weeds. Staple it to the inside of the boards, or straightforward lay it down and let the soil weight hold it in place. This step is optional—many gardeners skip it and manage weeds as they appear.

Filling and Settling

A 4-by-8-foot bed 12 inches deep needs about 32 cubic feet of soil. Buy bagged soil or bulk soil delivered by a landscape supplier. Bulk soil is cheaper if you are filling multiple beds; a single cubic yard (27 cubic feet) costs $30 to $50 delivered in most areas. Bagged soil costs more per cubic foot but is easier to handle if you have only one bed.

Fill the bed to about 1 inch below the rim. The soil will settle over the next week as it absorbs water and compacts. Do not plant when ready—wait 5 to 7 days and add more soil if needed. This settling prevents your plants from sinking as the soil underneath them compresses.

Water the soil thoroughly after filling. This speeds up settling and helps you see where the level ends up. If you are using a soil mix with compost, the settling will be more noticeable than if you use straight topsoil.

Maintenance and Lifespan

Cedar and composite beds need no treatment and will last for years. Untreated pine boards will start to soften and rot at the bottom corners after 3 to 5 years—this is normal and does not mean the bed is unusable. When rot becomes severe, you can replace just the affected boards instead of rebuilding the whole frame.

Every few years, add 1 to 2 inches of compost to the top of the soil. This replaces nutrients that plants have used and keeps the soil level consistent as it compacts. Over time, the soil will settle 1 to 2 inches per year, so topping it off keeps your bed at the right depth.

Frequently Asked Questions

Can I use reclaimed wood or pallets to build a raised bed?

Reclaimed wood works if you know its history—avoid wood that was treated with chemicals or used to store hazardous materials. Pallets are risky because many are treated with pesticides for shipping. If you do use pallets, choose ones marked "HT" (heat-treated) rather than "MB" (methyl bromide). Cedar or composite is safer and not much more expensive.

Do I need to line the bottom of the bed?

No. Landscape fabric or cardboard blocks some weeds but is optional. Many gardeners skip it and pull weeds as they appear. If you have a serious perennial weed problem (like bindweed or quackgrass), a barrier helps, but it will eventually break down and need replacement.

How deep should a raised bed be?

Twelve inches is the standard depth and works for most vegetables, herbs, and shallow-rooted plants. Root vegetables like carrots and parsnips need 12 to 18 inches. If you are growing only lettuce or herbs, 8 inches is enough. Deeper beds hold more soil and require more filling material, so choose based on what you plan to grow.

Can I build a raised bed on concrete or a patio?

Yes, but drainage becomes important. Soil in a bed on concrete will not drain into the ground below, so water pools at the bottom. Add drainage holes by drilling through the boards, or use a soil mix with extra perlite or sand to improve drainage. Alternatively, place the bed on soil where water can drain naturally.

What if the boards start to bow outward after filling?

Bowing happens when soil pressure pushes the boards apart. Prevent it by using thicker boards (2-by-12 instead of 2-by-10) or adding corner braces inside the frame. If bowing has already started, you can add a horizontal brace across the middle of the long sides, fastened to the inside of the boards with screws.