The bed frame can be as simple as 2x4s on top of the ground, or even patio retaining wall blocks. The size is up to you. A bed that's at least 6 inches high provides ease of access and gives roots plenty of room to grow.
These instructions describe building a 4-ft. by 6-ft. by 10-1/2-in. bed with 2x4 untreated lumber. Untreated lumber isn't rot-resistant, but it's a good option for edibles.
The wood to use for a raised bed is your decision. Here are some options:
Compared to untreated wood, pressure treated lumber lasts longer and is available at a comparable cost. Some types are specifically treated for ground contact. But keep in mind that even water-based treatments such as ACQ contain the fungicide and pesticide necessary to make it effective. Here are some practices that may address concerns about using it in raised beds.
STEP ONE
Measure and mark the length of the walls and cut the boards. Measure and cut 2x4s for corner posts to support the walls. They should be the height of the garden bed wall. You can also cut posts to install along the walls for additional strength.
Tip: For our frame, we cut six 6-ft. boards, six 3-ft.-9-in. boards, and ten 10-1/2-in. support posts. You can build this bed with ten 2-in. by 4-in. by 10-in. boards.
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STEP TWO
Clamp together the boards for each wall. Set the corner posts on top of the wall boards, flush with the ends of the 6-ft. walls and set back 1-1/2 in. from the ends of the shorter walls. Drill pilot holes and attach the posts with screws. If you cut additional posts, attach them as well.
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STEP THREE
Drill pilot holes and connect all the sides with screws to form a box. The posts should be on the inside of the bed.
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STEP FOUR
Place the frame in position and outline it with a shovel. Setting up the bed on the ground rather than a hard surface — such as concrete — allows proper root growth and drainage.
Note: A large frame is heavy and unwieldy. You may need a helper when it’s time to move it.
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STEP FIVE
Set the frame aside to remove the grass. Loosen the dirt with a spading fork to help your new plants' roots grow deeply into the ground.
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STEP SIX
Before you set the bed in place, staple wide-mesh hardware cloth to the bottom of the frame. The mesh helps keep weeds out, but earthworms can still get in to enrich the soil. As an alternative to hardware cloth, you can consider using landscape fabric or even newspaper to block weed growth from below, but keep in mind that weed seeds can fall onto the soil and germinate.
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STEP SEVEN
If the wood isn't rot-resistant, staple heavy-duty plastic along the inside walls before adding the soil.
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STEP ONE
Fill the bed with a mix of nutrient-rich soil and compost.
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STEP TWO
Set the plants in holes and lightly fill in with soil. Keep the soil loose around the plants to allow water to reach the roots.
Tip: If you use container plants, break up the root ball before planting.
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STEP THREE
The best time to water is morning or evening, when less water evaporates in the sun. Check the plant tags for additional recommendations.
Tip: A timer on a soaker hose can make as simple task like watering even easier.
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Consider adding a mesh cover to keep birds and rabbits away. You can build the frame with wood and PVC pipes. Consider adding a trellis next to the bed for vines and tall plants.
Tools, products, materials, techniques, building codes, and local regulations change; therefore, Lowe's assumes no liability for omissions, errors, or the outcome of any project. The reader must always exercise reasonable caution, follow current codes and regulations that may apply, and is urged to consult with a licensed professional if in doubt about any procedures.