What You Need Before You Start

A garden box is a wooden frame that sits on the ground and holds soil for growing vegetables, herbs, or flowers. You will need four pieces of untreated wood (cedar, composite, or pine), four corner brackets or L-brackets, a drill with a screwdriver bit, wood screws, a level, and a measuring tape. The wood should be at least 2 inches thick and 6 to 12 inches tall—taller boxes drain better and are easier on your back when you bend to plant.

Do not use pressure-treated wood from before 2004, as it contains arsenic. Modern pressure-treated wood is safe, but cedar and composite materials last longer and look better. Untreated pine is the cheapest option but will rot in 3 to 5 years. Composite materials (wood fibers mixed with plastic) cost more upfront but last 10 to 15 years and never need staining.

Measure the space where you want the box to sit. Most home gardeners build boxes 4 feet long by 2 feet wide by 8 inches deep—that size fits standard garden tools and is straightforward to reach across. Larger boxes are harder to reach into; smaller ones dry out faster.

Key Takeaways

  • Use untreated cedar, composite, or modern pressure-treated wood; avoid old pressure-treated wood and do not use plywood, which delaminates in wet soil.
  • A 4-by-2-foot box that is 8 inches deep holds enough soil for most vegetables and fits standard garden spaces.
  • Assemble the frame on level ground, check that corners are square with a measuring tape, and find corners with L-brackets and wood screws rather than nails.
  • Line the bottom with hardware cloth to keep burrowing animals out, then add landscape fabric to prevent weeds from growing up through the soil.
  • Fill the box with a mix of topsoil and compost rather than garden soil alone, which compacts and drains poorly.

Cutting and Preparing Your Wood

Cut your four pieces of wood to length. For a 4-by-2-foot box, cut two pieces 4 feet long and two pieces 2 feet long. A home improvement store will cut wood for free or a small fee if you do not have a saw at home. Sand the cut ends lightly with 80-grit sandpaper so they are not splintered.

Lay the four pieces on the ground in the shape of a rectangle. Do not assemble them yet. Place the box where you want it to sit permanently—moving a filled box is difficult. Check that the ground is reasonably level using a 2-foot level. If the ground slopes more than 1 inch over the length of the box, either level the ground or build the box on a slight slope so water drains downhill.

Assembling the Corners

Stand the four pieces upright in a rectangle. The two longer pieces should overlap the ends of the two shorter pieces, so the corners form a square. Drill two pilot holes (small starter holes) through each long piece into the end of each short piece, about 2 inches from the top and 2 inches from the bottom. Pilot holes prevent the wood from splitting when you drive the screw in.

Drive a 3-inch wood screw through each pilot hole. Use a drill with a screwdriver bit set to medium speed—too fast and the screw will strip the wood. An L-bracket bolted to the inside of each corner adds strength, especially for boxes larger than 4 by 4 feet. If you use brackets, drill holes through the bracket and wood, then bolt them together with bolts and washers rather than screws.

Check that all four corners are square by measuring diagonally from corner to corner. Both diagonal measurements should be the same length. If they are not, the box is racked (twisted). Loosen the screws slightly and tap the box with a rubber mallet until the diagonals match, then tighten the screws again.

Lining the Bottom and Preparing the Interior

Hardware cloth is a metal mesh that keeps rabbits, gophers, and other burrowing animals from eating your roots from below. Lay a piece of hardware cloth (1/4-inch mesh) across the bottom of the box and staple it to the inside of the wooden frame with a staple gun. Overlap the seams by 6 inches so animals cannot squeeze through the gaps.

Lay landscape fabric (a woven geotextile) over the hardware cloth. This prevents weeds from growing up through the soil while still allowing water to drain. Staple the fabric to the inside walls of the box, leaving a 2-inch gap at the top so soil does not touch the wood directly. The fabric will decompose over 2 to 3 years, but by then the soil will have settled and weeds will be easier to pull by hand.

If you are building on a patio or deck and do not want to line the bottom, you can skip the hardware cloth and fabric. The wood will rot faster where it touches concrete, but the box will still last several years.

Filling the Box With Soil

Do not fill the box with garden soil from your yard. Garden soil is heavy, compacts easily, and often contains weed seeds and disease. Instead, use a mix of topsoil and compost. A common recipe is 60 percent topsoil and 40 percent compost by volume. For a 4-by-2-foot box that is 8 inches deep, you will need about 5 cubic feet of soil—roughly 10 bags of bagged topsoil plus 5 bags of compost from a garden center.

Dump the topsoil and compost into the box and mix them together with a shovel. Water the soil lightly as you mix so the compost breaks down and blends evenly. The soil will settle over the first week, so fill the box slightly higher than the rim. After a week, add more soil if the level has dropped below 6 inches from the top.

If cost is a concern, you can fill the bottom half with wood chips or shredded leaves and the top half with the topsoil-compost mix. The wood chips will break down over time and improve drainage. Do not use glossy paper or cardboard with plastic tape, as the plastic will persist in the soil.

Protecting the Wood From Rot

Wood that touches wet soil rots faster than exposed wood. You can extend the life of your box by painting the interior with a non-toxic wood sealant or lining the interior walls with landscape fabric. Do not use paint or stain on the interior—they can leach chemicals into the soil. A clear, food-safe sealant made for raised beds is available at most garden centers.

Cedar and composite materials do not need sealing. Untreated pine will last longer if sealed, but even sealed pine will need replacement in 5 to 7 years. Modern pressure-treated wood does not need sealing and will last 10 to 15 years.

Positioning and Drainage

Place the box in a spot that receives at least 6 hours of direct sun for vegetables, or 3 to 4 hours for leafy greens. Make sure water can drain away from the box—do not build it in a low spot where rainwater pools. If your yard is very flat, you can tilt the box slightly so one end is 1 inch higher than the other.

Check the level one more time before you fill it with soil. Once the box is full, it is too heavy to move. If the ground settles unevenly after a few months, you can shim one side with a shim or a thin piece of wood to keep the box level.

Frequently Asked Questions

Can I use plywood for a garden box?

Plywood delaminates (the layers separate) when exposed to wet soil and will fall apart within one to two years. Use solid wood boards at least 2 inches thick instead. Plywood is fine for the bottom if you line it with hardware cloth and landscape fabric, but the sides should always be solid wood.

How deep does a garden box need to be?

Most vegetables need 8 to 12 inches of soil. Shallow-rooted plants like lettuce and spinach can grow in 6 inches, but tomatoes, peppers, and root vegetables need at least 10 inches. Deeper boxes also retain moisture better and are easier on your back when you bend to plant and harvest.

Do I need to use corner brackets?

Brackets are not required for small boxes (4 by 4 feet or smaller) if you use 3-inch wood screws and drill pilot holes. Larger boxes or boxes that will sit for many years benefit from L-brackets bolted to the inside corners. Brackets cost $5 to $15 per corner and add 30 minutes to assembly time.

What if my ground is not level?

A slope of up to 1 inch across the length of the box is acceptable—water will drain toward the low end. If the slope is steeper, either level the ground by digging out the high side and filling the low side, or build the box on a slight slope so water drains naturally. Do not force a box onto uneven ground; it will rack and the corners will separate.

Can I build a garden box on concrete or a deck?

Yes, but the wood will rot faster where it touches concrete because water cannot drain away. Place landscape fabric or cardboard under the box to slow rot. The box will still last 3 to 5 years on concrete, depending on the wood type. On a deck, use composite or cedar to avoid staining the deck with tannins from the wood.