Start with untreated wood, a level spot, and basic tools
A raised garden bed is a wooden or composite box you fill with soil and plant into. You can build one in a weekend with a drill, saw, level, and four pieces of lumber. The most common size is 4 feet by 8 feet by 12 inches deep, but you can adjust the dimensions to fit your space and what you want to grow.
The key decision is what material to use. Untreated cedar or composite lumber lasts longer than pressure-treated wood and won't leach chemicals into your soil. Pressure-treated wood is cheaper but contains preservatives that can break down over time. Avoid railroad ties and old pallets — they often contain creosote or other toxins. Composite materials like recycled plastic and wood fiber cost more upfront but last 15 to 20 years instead of 5 to 10.
You'll also need landscape fabric to line the bottom, which stops weeds from growing up through the bed. Cardboard works too and breaks down over time, adding organic matter to the soil.
Key Takeaways
- Untreated cedar or composite lumber is safer than pressure-treated wood because it won't release chemicals into the soil where you grow food.
- A standard 4-by-8-foot bed 12 inches deep holds about 32 cubic feet of soil and works for most vegetables and herbs.
- You need a level spot of ground, a drill with a screwdriver bit, a saw, a level, and four corner brackets or L-brackets to hold the frame together.
- Landscape fabric or cardboard on the bottom stops weeds from growing up into your bed and saves you weeding work later.
- The whole project takes two to four hours and costs between $100 and $300 depending on materials and size.
Measure your space and cut the lumber to length
Decide where your bed will sit. It needs at least six hours of direct sunlight for most vegetables, level ground so water doesn't pool in one corner, and access from at least two sides so you can reach the middle without stepping into the bed. Mark out the footprint with a tape measure and stakes.
Cut your lumber to length. For a 4-by-8-foot bed, you need two pieces 8 feet long and two pieces 4 feet long. If you don't have a saw, most home improvement stores will make these cuts for you for a small fee. Measure twice before cutting — a mistake here means buying new lumber.
Sand the cut edges smooth so they don't splinter when you handle them. This takes 10 minutes with medium-grit sandpaper and makes assembly safer.
Assemble the frame with corner brackets or screws
Lay the four pieces of lumber on the ground in a rectangle. The simplest way to join them is with L-brackets or corner brackets bolted to the inside corners. Drill pilot holes first — this stops the wood from splitting when you drive the bolts through. Use stainless steel bolts and washers so they don't rust.
Alternatively, you can screw the pieces together. Lay one long piece and one short piece at a right angle, then drive three 3-inch exterior wood screws through the short piece into the end of the long piece. Repeat for all four corners. This method is faster but creates a weaker joint than bolted brackets, especially if you plan to move the bed later.
Once the frame is assembled, set it in place on your marked spot. Use a level to check that all four corners are at the same height. If the ground slopes, dig out the high spots and fill in the low spots until the frame sits level. A bed that slopes will drain unevenly and make watering harder.
Line the bottom and add soil
Lay landscape fabric across the bottom of the frame, overlapping the seams by 6 inches. Staple it to the inside of the frame so it doesn't shift when you add soil. Landscape fabric lets water drain through while blocking weeds from growing up from the ground below.
If you don't have landscape fabric, lay cardboard instead. Overlap the pieces by 12 inches and wet them so they stay in place. Cardboard breaks down over two to three years and adds carbon to your soil, which is actually a benefit. Poke a few holes in it so water can drain.
Fill the bed with soil. A 4-by-8-foot bed 12 inches deep needs about 32 cubic feet of soil. You can buy this as bagged potting soil, garden soil, or topsoil, or order it in bulk from a landscape supplier. Bulk soil is cheaper per cubic foot but requires delivery. Mix in compost — about one part compost to three parts soil — so your plants have nutrients to start with.
Choose the right depth for what you're growing
Most vegetables need 12 inches of soil depth, which is the standard height for a raised bed. Shallow-rooted plants like lettuce, spinach, and herbs can grow in 8 inches. Root vegetables like carrots, beets, and parsnips need 12 to 18 inches so the roots have room to develop without hitting the bottom.
If you're building on top of clay or compacted soil, go deeper rather than shallower. The extra soil gives roots room to grow and keeps them from hitting hard ground. A 12-inch bed is a good compromise for most home gardens because it holds enough soil for most crops without requiring so much material that the cost becomes prohibitive.
You can also build a tiered bed — a taller frame on one side and shorter on the other — to create a slope that looks intentional and drains better. This requires cutting the side boards at an angle, which is more work but looks polished.
Prevent pests and protect the edges
If rabbits or deer are a problem in your area, you may need to add a fence or cage around the bed. A straightforward wire fence 2 feet tall stops rabbits. Deer need 6 feet or more, and some gardeners use electric fencing instead. This is optional and depends on what animals live near you.
Gophers and moles can tunnel up through the bottom of a raised bed. If you have these pests, line the bottom with hardware cloth — a metal mesh with half-inch holes — instead of or under the landscape fabric. Hardware cloth costs more and is harder to work with, but it stops burrowing animals completely.
Sand the top edge of the frame smooth or add a cap board — a 2-by-6 or 2-by-8 laid flat on top of the frame — so you don't get splinters when you lean on it. A cap board also makes the bed look finished and gives you a place to sit while you work.
Maintain the bed as it settles and ages
In the first year, the soil will settle as it compacts and as organic matter breaks down. You may need to add 2 to 4 inches of new soil or compost in spring before planting. This is normal and expected.
Check the frame for rot or damage each spring. Cedar lasts longer than pine, but even cedar will eventually split or warp. If you see soft spots or deep cracks, that board may need replacing. Untreated wood typically lasts 5 to 10 years before rot becomes a problem. Composite materials last much longer but cost more upfront.
Refresh the soil every three to five years by adding a 2-inch layer of compost on top. This replaces nutrients that plants have used and keeps the soil structure loose and workable. You don't need to replace all the soil — just add to it.
Frequently Asked Questions
Do I need to put anything on the bottom to stop weeds?
Yes. Landscape fabric or cardboard stops perennial weeds from growing up through the bed. Without it, you'll spend the season pulling weeds that grew from seeds in the ground below. Cardboard is cheaper and breaks down over time, adding organic matter. Landscape fabric lasts longer but doesn't add anything to the soil.
What's the difference between pressure-treated and untreated wood?
Pressure-treated wood is injected with preservatives to resist rot and insects. These chemicals can leach into soil over time, especially if you're growing food. Untreated cedar resists rot naturally and is safer for vegetable gardens, but it costs more and lasts 5 to 10 years instead of 10 to 15. For a food garden, untreated or composite is worth the extra cost.
Can I build a raised bed on top of grass?
Yes, but the grass will eventually rot and create air pockets under the bed. Lay cardboard or landscape fabric on top of the grass first, then set the frame on top. This smothers the grass and prevents it from growing up into your bed. The grass underneath will decompose and add organic matter to the soil.
How much soil do I need to fill a raised bed?
A 4-by-8-foot bed 12 inches deep needs about 32 cubic feet of soil. A 4-by-4-foot bed 12 inches deep needs 16 cubic feet. Most bags of potting soil are 2 to 3 cubic feet, so you'd need 10 to 16 bags for a standard bed. Bulk soil is cheaper per cubic foot if you're filling multiple beds.
Can I build a raised bed without tools?
You need at least a drill and a saw, or access to someone who can cut the lumber for you. A hand saw works if you don't have a power saw, but it takes longer. Most home improvement stores will cut lumber to length for free or a small fee, which saves you buying a saw if you only build one bed.