The Basic Steps to Build Your Raised Bed

A raised garden bed is a wooden or composite box you fill with soil and plant into—it takes a weekend to build and costs between $50 and $200 depending on materials. You'll need to choose a location, build or buy a frame, level the ground, add landscape fabric, fill it with soil, and plant. Most people finish in a single day once they have materials on hand.

The frame is the core of the project. You can build one from untreated wood boards (typically 2-by-10 or 2-by-12 lumber), buy a pre-made kit, or use composite materials like recycled plastic lumber. Untreated wood is cheapest and easiest to work with; it lasts 5 to 10 years before rotting. Composite materials cost more upfront but last 15 to 20 years.

Key Takeaways

  • Choose a location that gets at least 6 hours of direct sun per day and is relatively level, because water will pool in low spots.
  • Build or buy a frame, then level the ground underneath by removing grass and high spots so the frame sits flat.
  • Line the bottom with landscape fabric to block weeds, then fill with a mix of topsoil and compost rather than garden soil alone.
  • Fill the bed to within 2 inches of the top rim so soil doesn't spill over when you water.
  • Let the soil settle for a few days before planting, or plant right away if you water gently the first week.

Choosing the Right Location and Size

Pick a spot that receives at least 6 hours of direct sunlight daily—this is the single most important factor for vegetable growth. If you're growing leafy greens or herbs, 4 hours works. Check the sun pattern over a few days before you commit, because trees grow and shadows shift with the seasons.

Choose a level or nearly level spot. If the ground slopes, water will drain to the low end and leave the high end dry. You don't need perfectly flat ground—you'll level it during construction—but avoid steep hillsides. Also avoid spots directly under trees, where roots will compete with your plants and falling leaves will clog the bed.

Standard raised beds are 4 feet by 8 feet and 12 inches deep, but you can build any size. Smaller beds (3 by 6 feet) are easier to reach into and maintain. Deeper beds (18 inches) let you grow root vegetables like carrots and potatoes. Wider beds (more than 3 feet across) become hard to reach the center without stepping on soil.

Building or Buying the Frame

If you're building from wood, buy untreated 2-by-10 or 2-by-12 boards from a lumber yard or home center. Avoid pressure-treated wood, which contains chemicals that can leach into soil. Cedar and redwood resist rot naturally but cost more. For a 4-by-8 bed, you'll need four 8-foot boards and four 10-foot boards, plus 16 corner brackets or 3-inch wood screws.

Lay the boards on the ground in a rectangle. Attach the corners with L-shaped metal brackets bolted to the inside, or drill pilot holes and drive 3-inch exterior wood screws through one board into the end of the next. Metal brackets are faster and stronger; screws are cheaper. Make sure the frame is square by measuring diagonally from corner to corner—both measurements should be equal.

Pre-made kits come flat-packed and bolt together in 30 minutes. They cost $100 to $300 depending on size and material. Composite kits last longer than wood but weigh more and are harder to modify if you need a custom size. If you're building your first bed, a kit removes the guesswork.

Leveling the Ground and Laying Landscape Fabric

Set the frame in place and check that it sits flat. Use a 2-foot level across the frame in both directions. If one corner is high, dig out soil from under it. If one corner is low, add soil underneath. You don't need it perfectly level—within 1 inch of level is fine—but avoid tilting more than that.

Once the frame is level, remove grass and weeds from inside. You can dig them out by hand, spray them with herbicide a week before building, or straightforward lay cardboard over the grass and let it rot under the soil. Cardboard takes 2 to 3 months to break down but saves digging.

Lay landscape fabric over the bottom of the frame. This blocks weeds from growing up through the soil and keeps burrowing pests like moles out. Use a heavy-duty weed barrier (at least 3 ounces per square yard), not thin plastic sheeting. Overlap seams by 6 inches and staple or pin the fabric to the frame so it doesn't shift when you add soil.

Filling the Bed With Soil and Compost

Fill the bed with a mix of topsoil and compost, not garden soil alone. Garden soil compacts over time and drains poorly in a raised bed. A good mix is 60 percent topsoil and 40 percent compost by volume. For a 4-by-8-by-12-inch bed, you'll need about 32 cubic feet of soil, or roughly 1.2 cubic yards.

Buy topsoil and compost by the cubic yard from a landscape supply company or garden center. Bags from a hardware store work but cost more per cubic yard and create a lot of waste. Ask the supplier to deliver if you're buying more than a half cubic yard—it's cheaper than hauling bags yourself.

Dump the soil into the bed and spread it evenly with a shovel or rake. Fill to within 2 inches of the top rim. Soil will settle over the first few weeks, dropping 1 to 2 inches. If you fill to the brim, water will wash soil over the edge. Water the bed thoroughly after filling so the soil settles faster.

Planting and Watering Your New Bed

You can plant when ready after filling, or wait a few days for the soil to settle. If you plant right away, water gently for the first week so you don't wash soil around the roots. Most vegetables and herbs grow well in a new raised bed without any additional amendments.

Water the bed deeply and regularly. Raised beds drain faster than in-ground gardens, so check soil moisture every 2 to 3 days in warm weather. Stick your finger 2 inches into the soil—if it feels dry, water. In hot weather, you may need to water daily. Mulch the surface with 2 inches of wood chips or straw to slow evaporation.

As seasons pass, the soil will compact and compost will break down. Add 1 to 2 inches of compost each spring to maintain soil quality. After 3 to 5 years, you may need to replace the top 6 inches of soil if it becomes compacted or depleted.

Common Mistakes to Avoid

The most common error is filling the bed with garden soil or potting mix alone. Garden soil compacts and holds water; potting mix drains too fast and costs too much. Use the topsoil-and-compost mix described above. Another mistake is building on uneven ground and not leveling it first. Water will pool on one side and dry out on the other, killing plants unevenly.

Don't skip the landscape fabric. Weeds will grow through the bottom and compete with your plants. Also avoid pressure-treated wood, which can leach chemicals into soil over time. Finally, don't fill the bed all the way to the rim. Soil will settle and water will overflow, and you'll have nowhere to add mulch.

Frequently Asked Questions

How deep does a raised bed need to be?

Most vegetables need 12 inches of soil. Root vegetables like carrots and potatoes need 18 inches. Leafy greens and herbs grow fine in 8 inches. Deeper beds hold more water and stay warmer in spring, but they cost more to fill and are heavier to move.

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

Yes, but you'll need to drill drainage holes in the bottom or add a layer of gravel so water doesn't pool. Concrete heats up in summer and can warm the soil too much, so consider partial shade or extra mulch. You'll also need to water more often because concrete doesn't absorb moisture.

What's the best soil mix for a raised bed?

A mix of 60 percent topsoil and 40 percent compost works for most plants. Some gardeners use equal parts topsoil, compost, and peat moss or coconut coir for better water retention. Avoid pure compost, which is too rich and drains poorly, and pure garden soil, which compacts.

How long does it take for soil to settle?

Most settling happens in the first 2 to 4 weeks. You'll see the biggest drop in the first week after watering. Soil continues to settle slowly over months as compost breaks down and particles compact, but it's stable enough to plant when ready.

Do I need to add fertilizer to a new raised bed?

No. A fresh mix of topsoil and compost has enough nutrients for the first season. After that, add 1 to 2 inches of compost each spring or use a balanced fertilizer during the growing season if plants look pale or weak.