Start with the frame: wood, composite, or metal

A raised bed is a box that sits on top of your ground. The frame is what holds the soil in place. You have three main choices: untreated wood (usually cedar or pine), composite boards (plastic and wood fiber mixed), or galvanized metal.

Untreated wood is the cheapest and easiest to work with. Cedar lasts 10 to 15 years before rot sets in; pine lasts 5 to 10 years. You can buy pre-cut cedar boards at most garden centers, or ask the lumber yard to cut 2-by-10 or 2-by-12 boards to length. Composite boards cost more upfront but last 20+ years and don't need sealing. Metal frames (usually steel or aluminum) are durable and look clean, but they heat up in direct sun and can be harder to find locally.

Do not use pressure-treated wood from before 2004—it contains arsenic. Modern pressure-treated wood is safe for vegetable gardens, but many gardeners avoid it anyway and choose cedar instead.

Key Takeaways

  • A raised bed frame can be built from untreated cedar boards, composite materials, or metal, each with different lifespans and costs.
  • You will need to assemble the frame with corner brackets or screws, then place it on level ground and line the bottom to block weeds.
  • Fill the bed with a mix of topsoil and compost rather than garden soil alone, which compacts over time.
  • The bed should be at least 6 inches deep for shallow-rooted crops like lettuce, and 12 inches deep for tomatoes, peppers, and root vegetables.
  • Drainage and sunlight matter more than the exact location—most vegetables need 6 to 8 hours of direct sun and soil that doesn't stay waterlogged.

Assemble the frame with corner brackets or screws

Once you have your boards, you need to join them at the corners. The two most common methods are L-brackets and wood screws.

L-brackets (also called corner braces) are metal plates that bolt or screw to the inside of two boards at a right angle. They are fast and strong. Drill pilot holes first so the wood doesn't split, then drive 3-inch bolts or lag screws through the bracket into each board. You need one bracket per corner, so four total for a rectangular bed.

Wood screws are simpler if you have a drill. Lay two boards perpendicular to each other, then drive 3-inch exterior-grade screws through the face of one board into the end grain of the other. Use at least three screws per corner, spaced a few inches apart. Exterior-grade screws won't rust; interior drywall screws will corrode in soil moisture.

If your boards are longer than 8 feet, add a support board down the middle to prevent the sides from bowing outward under the weight of wet soil.

Level the ground and block weeds from below

Set the assembled frame on the spot where you want it. Use a level to check that the top edges are even—if one corner is higher, dig out soil or add soil underneath until it is flat. A tilted bed will drain unevenly and make watering harder.

Once the frame is level, lay down a barrier to stop grass and weeds from growing up into your bed. Cardboard works well: flatten boxes, overlap them by a few inches, and lay them inside the frame. Landscape fabric (the black or tan woven kind, not plastic sheeting) also works and lasts longer. Staple or pin the fabric to the inside of the frame so it doesn't shift when you fill the bed. This step is optional if you don't mind weeds, but it saves work later.

Do not use plastic sheeting—it traps water and creates soggy soil.

Fill the bed with soil and compost

Never fill a raised bed with garden soil alone. Garden soil compacts when wet and stays dense, which roots hate. Instead, use a mix: roughly 60 percent topsoil and 40 percent compost, or follow the "Mel's Mix" formula of one-third compost, one-third peat moss or coconut coir, and one-third vermiculite.

For a 4-by-8-foot bed that is 12 inches deep, you will need about 32 cubic feet of soil. Most garden centers sell soil by the cubic yard (27 cubic feet), so order one cubic yard and you will have a little left over. Compost is usually sold in bags; a 2-cubic-foot bag covers about 8 square feet at 3 inches deep.

Dump the soil and compost into the bed and mix them together with a shovel. The bed will settle over the first few weeks as the soil compacts naturally, so fill it slightly higher than the rim. Water it well after filling—this helps the soil settle and removes air pockets.

Choose the right depth for what you want to grow

Shallow-rooted crops like lettuce, spinach, and radishes need only 6 inches of soil. Medium-rooted crops like beans, chard, and beets need 8 to 10 inches. Deep-rooted crops like tomatoes, peppers, carrots, and parsnips need 12 inches or more.

If you are building a single bed and want to grow a mix, go with 12 inches as a safe middle ground. You can always add more soil later if a crop needs it, but you cannot remove soil easily once the bed is full.

Taller beds (18 to 24 inches) are easier on your back if you have mobility issues, but they dry out faster and need more soil to fill.

Position the bed for sun and drainage

Most vegetables need 6 to 8 hours of direct sun per day. Leafy greens tolerate 4 to 6 hours. Tomatoes, peppers, and squash need the full 8 hours. Walk around your yard at different times of day and watch where shadows fall—that tells you which spots get sun.

Drainage matters as much as sun. Do not place the bed in a low spot where water pools after rain, or in a spot where runoff from a roof or driveway flows through. Soggy soil causes root rot and fungal disease. If your yard is naturally wet, build the bed on a slight slope or add a drain line under the frame before filling it.

Avoid placing the bed directly against a fence or wall if possible—it limits air flow and makes the back side hard to reach. Leave at least 2 feet of space on all sides if you can.

Frequently Asked Questions

Do I need to treat the wood with sealant or stain?

No. Untreated wood will rot eventually, but that is normal and expected. Sealants and stains can leach chemicals into the soil, especially if they are not food-safe. It is better to let the wood weather naturally and replace the boards when they rot—usually 5 to 15 years depending on the wood type.

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

Yes, but drainage becomes your problem. Concrete and asphalt do not absorb water, so any rain or watering that drains through the bed will pool underneath and keep the soil wet. Drill or drill holes in the bottom of the frame, or set the frame on spacers (concrete blocks or wood strips) so water can run out underneath.

What if I want to build a very large bed or an unusual shape?

Rectangular beds are easiest to build and fill. If you want something larger than 4 by 8 feet, add support boards down the middle to prevent the sides from bowing. For L-shaped or curved beds, composite boards or metal are easier to work with than wood. Very large beds (over 100 square feet) are better built as two separate beds—they are easier to reach into and easier to fill.

Should I add fertilizer or amendments before planting?

Good compost already contains nutrients, so you do not need to add fertilizer right away. After the first season, mix in 1 to 2 inches of fresh compost each spring to replenish nutrients. If a soil test shows you are low in specific nutrients (nitrogen, phosphorus, or potassium), add those amendments based on the test results.

How long does it take to build a raised bed?

Assembly takes 30 minutes to an hour if you have the boards cut and the tools ready. Filling takes another hour or two depending on how much soil you are moving and whether you are mixing it by hand. If you order soil delivered, the whole project is usually done in an afternoon.