What You Need Before You Start
Building a raised garden bed takes a weekend and costs between $50 and $300 depending on size and materials. You will need untreated wood boards (cedar, composite, or pine), corner brackets or a corner kit, a drill or screwdriver, soil to fill it, and a level. Most people use 2-by-10 or 2-by-12 boards for the sides, which give you 10 or 12 inches of depth — enough for most vegetables and herbs.
The location matters before you buy anything. Pick a spot that gets at least six hours of direct sun, is reasonably level, and has access to water. Measure the space and decide on dimensions. A 4-by-8-foot bed is standard and fits most yards; a 3-by-6-foot bed is easier to reach across. Write down your measurements before you go to the hardware store.
Untreated cedar lasts 10 to 15 years and resists rot naturally, but costs more upfront. Composite boards last longer and never rot, but cost two to three times as much. Pressure-treated wood is cheaper and durable, though some gardeners avoid it because of the chemicals. Pine is the budget option but will rot in five to seven years. Choose based on how long you want the bed to last and what you can spend.
Key Takeaways
- Untreated cedar or composite boards are the best long-term choice; pressure-treated wood is cheaper but contains chemicals some gardeners prefer to avoid.
- A standard 4-by-8-foot bed requires eight 8-foot boards (four for each long side, two per short side), corner brackets, and about 32 cubic feet of soil.
- The bed must sit on level ground or the water will pool on one side and dry out on the other, so check with a level before you fill it.
- You can assemble the frame on the ground, then move it into place, or build it in place — moving it is easier if the bed is small.
- Landscape fabric under the bed stops weeds but is optional; many gardeners skip it and pull weeds as they appear.
Cutting and Gathering Your Materials
Most hardware stores will cut boards to length for free or a small fee. If you are building a 4-by-8-foot bed, you need four 8-foot boards for the long sides (two boards stacked per side) and four 4-foot boards for the short sides (two boards stacked per side). If you are building a 3-by-6-foot bed, you need four 6-foot boards and four 3-foot boards. Write your exact dimensions on a piece of paper and bring it with you.
For corners, you have two options: metal L-brackets (usually $3 to $8 per bracket, and you need four) or a corner kit designed for raised beds (usually $15 to $40 for a set of four). Corner kits are easier because they hold the boards at the right angle automatically. L-brackets work fine but require more precision when you tighten them.
Gather a power drill or a hand screwdriver, 3-inch exterior wood screws (about 16 to 20 for a standard bed), a level, and a tape measure. If you are using landscape fabric, buy enough to cover the bottom with a few inches of overlap at the edges.
Assembling the Frame on the Ground
Lay all four boards on a flat surface in the shape of a rectangle. If you are using corner brackets, position them at each corner on the inside of the frame, then drill pilot holes (small starter holes) and screw the brackets to both boards. If you are using a corner kit, slide the boards into the kit slots and tighten the bolts or screws that come with it.
Check that the frame is square by measuring diagonally from corner to corner — both measurements should be the same. If they are not, adjust the frame until they match. Once the frame is square and all corners are tight, flip it over and check the outside corners for gaps. Tighten any loose screws.
If your bed is large (more than 4 feet wide), add a center support board running lengthwise down the middle, attached with brackets at each end. This prevents the long sides from bowing outward when the soil is wet and heavy.
Moving the Frame Into Place and Leveling
If the bed is small enough to carry (under 50 pounds empty), move it to your chosen location. If it is large or heavy, build it in place instead — lay out the boards where they will sit, attach the corners, and skip ahead to the leveling step.
Set the frame down and place a level on the inside bottom, checking both directions (front to back and side to side). If one side is higher, you have two choices: dig out soil under the high side to level the ground, or accept a slight slope and water more often on the high side. Most gardeners dig out a little soil and call it level enough if the bubble is close to center.
Once the frame is level, check that all corners are still tight and that the frame sits flat against the ground with no gaps underneath. If there are gaps, the frame will settle unevenly as the soil weight shifts.
Lining the Bottom and Adding Soil
Landscape fabric is optional. It stops weeds from growing up through the bottom but also slows drainage slightly. If you use it, lay it across the bottom, staple it to the inside of the frame, and trim the excess. If you skip it, you will pull more weeds by hand but have slightly faster drainage.
Fill the bed with soil. For a 4-by-8-foot bed that is 10 inches deep, you need about 30 cubic feet of soil. Most garden centers sell soil by the cubic yard (27 cubic feet), so you will need just over one cubic yard. Buy a mix of topsoil and compost — usually 50/50 or 60/40 — rather than pure topsoil, which compacts and drains poorly. Avoid "potting soil," which is too light and expensive for a large bed.
Shovel the soil in and rake it level. The soil will settle over the first few weeks, so fill it slightly higher than the top of the frame. Water it thoroughly after filling to help it settle and to give you a baseline for how much water the bed holds.
Securing the Frame and Preventing Collapse
Once the bed is full of soil, the weight pushes outward on the sides. If your boards are thin or your bed is very wide, the sides can bow. To prevent this, drive a stake (a 2-by-2 or a metal rod) into the ground outside each corner, then attach the frame to the stake with a bracket or by screwing through the board into the stake.
Alternatively, run a cable or strap across the top of the bed from side to side, tightened with a turnbuckle. This is less visible than stakes and works well for beds that are 4 feet or wider. For narrow beds (3 feet or less), corner brackets alone are usually enough.
Check the frame after the first heavy rain or watering. If the sides have bowed, tighten the brackets or add stakes. Soil that is too wet is heavier and pushes harder, so this is most likely to happen in spring or after heavy rain.
Maintenance and When to Replace
Wood boards will eventually rot, even untreated cedar. Check the bottom corners and the joints every year — these rot first because water pools there. If you see soft wood or discoloration, that board is starting to fail. You can replace a single board by unbolting the corners, sliding the old board out, and sliding a new one in.
Composite boards do not rot but can crack or fade. Metal brackets may rust over time, especially if you live near the coast. Stainless steel brackets cost more but last longer than galvanized ones.
Most raised beds last five to ten years with cedar, ten to twenty with composite, and three to seven with pine. Budget for replacement or repair when planning your garden.
Frequently Asked Questions
Can I build a raised bed on top of grass without removing it first?
Yes, but the grass will decompose under the bed and create air pockets that settle over time. The bed will sink unevenly. It is better to remove the grass first or lay cardboard under the frame to smother it. If you skip both steps, expect the bed to settle by 2 to 4 inches in the first year.
How deep does a raised bed need to be?
Ten inches is the minimum for most vegetables and herbs. Twelve inches is better for root crops like carrots and potatoes. Lettuce and greens can grow in 6 inches. Deeper beds hold more water and give roots more room, so go deeper if you can.
What size raised bed should I build?
A 4-by-8-foot bed is standard and fits most yards. A 3-by-6-foot bed is easier to reach across without stepping into the middle. Avoid beds wider than 4 feet unless you plan to reach from both sides, because you will step on the soil in the middle and compact it.
Do I need to treat the wood with anything?
No. Do not paint or seal untreated wood — the sealant can leach into the soil. Untreated cedar and composite boards are naturally rot-resistant. If you use pine or pressure-treated wood, leave it as is.
Can I use reclaimed wood or pallets?
Pallets are often treated with chemicals for shipping and are not safe for food gardens. Reclaimed wood can work if you know its history and it has not been treated with pesticides or preservatives. New untreated boards are safer and not much more expensive.