Start with untreated wood, landscape fabric, and soil — here's what you actually need

A raised garden bed is a wooden or composite box you fill with soil and plant into. To build one, you need four boards (usually cedar or composite), corner brackets or screws, landscape fabric to line the bottom, and soil to fill it. The whole job takes two to four hours and requires only a drill, saw, and level. You do not need concrete footings, special tools, or a contractor — just straight boards, a way to join them at the corners, and the ability to measure twice.

The most common mistake is using pressure-treated wood that contains chemicals, or boards that are too thin to hold soil weight. Cedar lasts ten to fifteen years without treatment. Composite boards last longer but cost more. Either way, buy boards at least one inch thick and untreated.

Key Takeaways

  • Cedar or composite boards at least one inch thick are the only materials worth buying; pressure-treated wood contains chemicals that leach into soil over time.
  • Corner brackets bolted through the boards are stronger and faster than screws alone, and they let you build without a helper.
  • Landscape fabric stapled to the inside bottom stops weeds from growing up through the bed without blocking drainage.
  • Fill the bed with a mix of topsoil and compost rather than garden soil alone, which compacts and drains poorly.
  • A level bed drains evenly and looks finished; check it before you fill it, because moving it after is much harder.

Choose your boards and cut them to length

Buy untreated cedar, redwood, or composite boards. Cedar is the standard because it resists rot, costs less than composite, and lasts long enough to justify the work. Composite boards (made from wood fiber and plastic) last twenty years or more but cost two to three times as much per board. Pressure-treated wood is cheaper but leaches copper and arsenic into soil — avoid it for vegetable beds.

Boards should be at least one inch thick (one-by lumber, not half-inch plywood). A four-by-eight-foot bed needs four boards: two at eight feet and two at four feet. If you want a different size, write it down before you go to the store. Most home centers will make one or two cuts for free if you buy the boards there.

Lay the boards on a flat surface and check that the corners are square by measuring diagonally from corner to corner — both diagonals should be the same length. If they are not, adjust the boards until they are.

Attach the corners with brackets or screws

The strongest method is corner brackets bolted through both boards at each corner. Buy four L-shaped steel or composite brackets rated for outdoor use. Drill a hole through each bracket hole, then bolt them tight with washers and nuts. This takes fifteen minutes and requires only a drill and wrench. You can do it alone and the bed will not rack (twist) when you fill it.

The faster method is deck screws driven through one board into the end grain of the other. Use three-inch exterior-grade deck screws (at least three per corner) and a drill with a screw bit. Drill a pilot hole first so the board does not split. This method is weaker than brackets but works fine for beds up to four feet wide. Do not use nails — they pull out as the wood dries.

If you choose screws, have a helper hold the boards square while you drive them, or use a speed square to hold the angle. Brackets let you work alone.

Line the bottom with landscape fabric

Landscape fabric stops perennial weeds from growing up through the bed while letting water drain through. Lay it across the inside bottom of the bed and staple it to the inside of the boards with a staple gun. Overlap seams by at least six inches. Do not use plastic sheeting — it blocks drainage and creates a swamp.

If you are building on bare ground with no existing weeds, you can skip the fabric. If you are building over a lawn or weedy area, the fabric is worth the twenty minutes it takes. Staple it loosely enough that it does not tear when you pour soil on top.

Level the bed and position it in place

Set the bed in its final location before you fill it. Use a level to check that the ground underneath is flat — if one corner is high, dig out soil until the bed sits level. A bed that is not level will drain unevenly and look crooked.

If the ground is very uneven, you have two choices: dig the bed into the ground so the top is level, or build a second layer of boards on the downhill side to level it. Digging is faster. Leveling with boards is better if you want the bed to sit on top of the ground.

Once the bed is level and in place, you are ready to fill it. Do not move it after you add soil — it will be too heavy.

Fill the bed with soil and compost

Do not use garden soil alone — it compacts when wet and drains poorly. Instead, mix topsoil and compost in equal parts, or use a raised bed mix (topsoil, compost, and peat or coco coir blended together). A four-by-eight-foot bed twelve inches deep holds about thirty-two cubic feet of soil. Order it delivered if you can — carrying bags is slow and your back will hurt.

Spread the soil evenly and rake it level. Water it lightly and let it settle for a day before you plant. The soil will compact slightly as it dries, so you may need to add more after a week.

Frequently Asked Questions

Do I need to put anything under the bed to stop gophers or moles?

If gophers or moles are a problem in your area, line the bottom with hardware cloth (a metal mesh) before you add landscape fabric. Staple it to the inside of the boards so it does not move. This adds cost and time but stops burrowing animals from eating your roots.

Can I use old pallets to build a raised bed?

Pallets are free but often treated with chemicals or pesticides. If you use them, make sure they are marked HT (heat-treated) rather than MB (methyl bromide). Even then, line the inside with plastic sheeting to keep soil from touching the wood. New cedar boards are safer and not much more expensive.

How deep should the bed be?

Twelve inches is the minimum for most vegetables. Root crops like carrots and potatoes need eighteen inches. Shallow beds work for lettuce and herbs. Deeper beds drain better and give roots more room, so go deeper if you can afford the soil.

What if the ground is concrete or asphalt?

You can build on concrete without any preparation. Water will not drain through, so drill a few half-inch holes in the bottom boards or add a layer of gravel under the landscape fabric. This lets water escape instead of pooling.

How long does it take for a raised bed to pay for itself?

That depends on what you grow and how much you would spend at a farmers market. A four-by-eight bed costs fifty to two hundred dollars in materials and produces thirty to fifty pounds of vegetables in a season. If you grow tomatoes, peppers, or herbs, you will recover the cost in the first year. Leafy greens take longer because they are cheap to buy.