What You Need Before You Start

A wooden raised bed is a box frame you fill with soil and plant into. You build it from untreated wood boards, assemble them at the corners, and set it on level ground. The whole job takes four to six hours and requires only a drill, a saw, and basic fasteners — no special skills or experience needed.

The most common size is 4 feet by 8 feet by 12 inches deep, which fits standard garden spaces and holds enough soil for most vegetables. You can build smaller (2 by 4 feet works for herbs or flowers) or larger, but the 4-by-8 frame is the easiest to source materials for and to work with alone.

Untreated wood is essential. Pressure-treated lumber contains chemicals that leach into soil over time. Cedar and redwood naturally resist rot and are the best choices, though they cost more. Pine and fir work too but will rot in five to seven years depending on your climate. Avoid treated wood entirely — the cost difference is not worth the risk to plants you will eat.

Key Takeaways

  • Buy untreated cedar, redwood, or pine boards in the dimensions you need — typically 2-by-10 or 2-by-12 lumber — and have the store cut them to length if you lack a saw.
  • Assemble the frame on level ground using 3-inch exterior-grade screws at each corner, drilling pilot holes first to prevent the wood from splitting.
  • A 4-by-8-foot bed 12 inches deep requires eight boards (four long, four short), four corner posts, and sixteen screws.
  • Fill the bed with a mix of topsoil and compost, not garden soil alone, because garden soil compacts and drains poorly in a confined space.
  • Let the bed settle for a week before planting, and water it thoroughly so the soil compacts naturally.

Choosing and Buying Your Wood

The most practical choice for a first bed is cedar or redwood 2-by-10 boards. These are 9.25 inches tall when installed, which is deep enough for most vegetables and shallow enough to reach across comfortably. A 4-by-8-foot bed needs four boards 8 feet long and four boards 4 feet long. If your store cuts lumber, ask them to rip the boards to length — this saves you the cost and hassle of a saw rental.

You will also need four corner posts, typically 4-by-4 lumber cut to 12 inches each. These anchor the corners and prevent the frame from racking (twisting out of square). Some builders skip corner posts and use L-brackets instead, but posts are stronger and last longer.

For fasteners, buy 3-inch exterior-grade wood screws — the kind coated to resist rust. You need sixteen screws total (four per corner, two screws per joint). Exterior-grade matters because interior screws will rust and stain the wood and soil. Avoid nails; they work loose as the wood settles and the bed shifts with frost heave in winter.

Preparing the Site and Leveling

Choose a spot that gets at least six hours of direct sun and is reasonably level. A slope of more than a few inches will cause water to pool on one side and dry out on the other. If your yard slopes, you have two options: build the bed level and backfill the downhill side with soil, or dig out the high side and use that soil to fill the low side.

Clear the ground of grass and weeds. You do not need to remove the sod entirely — you can lay cardboard or newspaper over it and the bed will smother it over the first season. This saves digging and the cardboard breaks down into the soil. If you skip this step, grass and weeds will grow up through the bed and compete with your plants.

Check that the ground is level using a long straight board and a basic level. Place the board across the footprint of the bed and set the level on top. If the bubble is not centered, shim the low side with soil or dig out the high side. Spend ten minutes on this — a bed that is off-level will drain unevenly and look crooked.

Assembling the Frame

Lay out the four corner posts on the ground in a rectangle, spaced to match your board lengths. If you are building a 4-by-8 bed, the posts should be 4 feet apart on two sides and 8 feet apart on the other two. Place the first long board against two corner posts and align it so the top edges are flush.

Drill a pilot hole before driving each screw — this is the single most important step. A pilot hole is a small hole drilled straight through the board into the post, sized slightly smaller than the screw shaft. It prevents the wood from splitting and makes the screw drive in straight. Use a drill bit about half the diameter of your screw. Drill two holes per joint, one near the top and one near the bottom of the board.

Drive a 3-inch screw through each pilot hole into the corner post. Use a drill with a screw-driving bit, not a manual screwdriver — it is faster and more consistent. The screw should pull the board and post tight together with no gap. Repeat this for all four sides. Check the corners with a square to make sure they are 90 degrees. If a corner is off, loosen one screw, tap the frame into square, and retighten.

Filling and Settling the Bed

Do not fill the bed with garden soil from your yard. Garden soil is heavy, compacts easily, and drains poorly when confined in a raised bed. Instead, use a mix of topsoil and compost — roughly equal parts. This blend drains well, holds moisture, and provides nutrients for the first season. A 4-by-8-foot bed 12 inches deep holds about 32 cubic feet of soil, or roughly 1.2 cubic yards. Most landscape suppliers sell this by the yard and will deliver.

Spread the soil mix evenly in the bed and water it thoroughly. The soil will settle over the next week as it absorbs water and compacts naturally. Do not pack it down by hand — let gravity and water do the work. After a week, the level will drop an inch or two. Top it off with more compost if needed, then plant.

Maintenance and Longevity

Cedar and redwood beds last ten to fifteen years with no maintenance. Pine and fir last five to seven years. When the wood begins to rot (usually at the bottom corners where moisture collects), you can replace individual boards rather than the whole bed. Loosen the screws, slide out the rotted board, and slide in a new one.

Every few years, add a layer of compost to the top as the soil settles and breaks down. This keeps the nutrient level high and the drainage consistent. Do not add more than an inch per year or the bed will overflow.

Frequently Asked Questions

Can I use treated lumber if I seal it?

No. Pressure-treated lumber is treated with chemicals that prevent rot but can leach into soil, especially in wet conditions. Sealing the inside does not stop leaching. Untreated cedar or redwood costs more upfront but is safer for food gardens and lasts long enough to justify the price.

What if my ground is not level?

You can build on a slope up to about 4 inches of drop across the bed. Dig out the high side and use that soil to backfill the low side. If the slope is steeper, consider building two smaller beds at different heights or terracing the slope with multiple beds stacked on top of each other.

How deep does a raised bed need to be?

Most vegetables need 8 to 12 inches of soil depth. Shallow-rooted crops like lettuce and herbs work in 6 inches. Root vegetables like carrots and beets need 12 inches or more. A 12-inch bed is the practical minimum if you want to grow a variety of plants.

Do I need a bottom or drainage holes?

No. Water drains naturally into the ground below. If your ground is clay or compacted, you can lay landscape fabric on the bottom to slow drainage, but do not seal it completely or water will pool. Drainage holes are not necessary and will let soil wash out during heavy rain.

Can I build a raised bed without corner posts?

Yes, but it is not recommended. Without posts, the corners will rack (twist) as the wood settles and the frame will go out of square. L-brackets can reinforce corners, but they are more expensive than 4-by-4 posts and still less stable. Posts are the simplest and strongest option.