Setting up a raised bed
This guide covers both framed raised beds and mounded, unframed ones. A common size is 4 feet wide by 8 feet long by 1 foot deep, which gives 32 square feet of growing surface. You can build a basic frame in an afternoon. A bed of that size can hold six to eight large tomato plants. You will pick a sunny spot, set the width and height, choose safe materials, and fill the bed with a mix that drains well. Soil in a raised bed also warms more quickly than ground soil. The steps below follow that order.
When: Spring (Mar–May)
When to do it
Soil in raised beds warms more quickly in the spring than ground soil. Once the bed is filled, let the soil settle for a few days before you plant. Mix fertilizer into the top 6 inches of the bed just before planting. After each planting season, top off the soil to bring it back up to the original planting level. Each winter, cover the beds with 2 inches of leaves or other organic material. Collect a soil test every 2 to 3 years. The best time of day to water is early in the morning. Seedlings require more frequent irrigation for short durations than established plants.
What you need
Cedar or redwood is a long-lasting, safe choice for the frame. Untreated pine or fir also works, and a basic frame uses six 2-inch by 6-inch by 8-foot pieces. Pre-cast concrete blocks are acceptable for edible beds. If you use treated lumber, choose wood labeled UC4A or higher and rated for horticultural use. Railroad ties and older pressure-treated wood may contain creosote or other chemicals, so leave them out. You will also need a 2-inch by 2-inch by 1-foot corner post for each inside corner, plus forty-eight 3-inch wood screws or deck screws. Use stainless steel screws with pressure-treated lumber. For the bottom, gather 1/4-inch hardware cloth, plain cardboard, or black landscape fabric. For fill, gather topsoil, plant-based compost, and a drainage material such as coconut coir. A balanced, slow-release vegetable fertilizer or a 10-10-10 is suitable. Heavy-duty plastic sheeting is an option as a liner inside a treated-lumber bed.
Step by step
- Step 1
A good site gets at least 6 to 8 hours of direct sun each day
Also choose a well-drained spot that is close to a water source.
- Step 2
Find a level spot for the bed, or one that needs only minor changes to become level
Before you build, strip off the top layer of grass, or smother it with cardboard or several layers of newspaper.
- Step 3
Keep the bed only as wide as you can comfortably reach from either side, about 3 to 4 ft (0.9-1.2 m)
Most people can only reach about 2 ft (0.6 m) toward the middle, so beds work best at 4 ft (1.2 m) wide or less. For a bed deeper than 12 in (30 cm), limit the width to 6 ft (1.8 m) or less.
- Step 4
Choose boards 6 ft (1.8 m) long or shorter for the sides of the frame
Shorter boards are less likely to warp or break than longer ones. A common bed size is 4 ft by 8 ft by 1 ft (1.2 x 2.4 x 0.3 m). That gives 32 sq ft (3 m²) of growing space.
- Step 5
Decide how tall to build the frame, starting at a minimum of 6 in (15 cm)
Frames for gardeners with mobility challenges can go as tall as 24 in (61 cm). A height of about 27 in (69 cm) works well for wheelchair access. Some sources recommend a depth of 18 to 24 in (46-61 cm), though a bed that deep drains less well. For an unlined, mounded bed with no frame, aim for a finished height of 4 to 8 in (10-20 cm).
- Step 6
For enclosed, framed beds, leave a walkway 3 to 4 ft (0.9-1.2 m) wide
For mounded, unlined beds, a path 2 to 3 ft (0.6-0.9 m) wide is comfortable. Other guidance puts the walkway at 18 to 24 in (46-61 cm) wide. Other sources recommend leaving at least 3 ft (0.9 m) between beds instead. Plan for a wider 30 in (76 cm) walkway anywhere a wheelbarrow needs to pass.
- Step 7
Avoid railroad ties and older pressure-treated wood that may contain creosote or other chemicals
Cedar or redwood is a long-lasting, safe choice for an edible bed, and pre-cast concrete block also works well. If you use treated lumber instead, pick wood labeled UC4A or higher, which is rated for horticultural use.
- Step 8
Build a basic frame from six 2x6 boards, each 8 ft (2.4 m) long, in untreated pine or fir
Add a 2 in by 2 in by 1 ft (5 x 5 x 30 cm) corner post inside each corner for support. Secure the frame with forty-eight 3 in (7.6 cm) wood screws or deck screws, 12 at each corner. Reinforce beds longer than 6 ft (1.8 m) or taller than about 18 in (46 cm) with cross cable or anchored stakes. Before you fill the bed, check that the tops of all corner posts sit at the same height.
- Step 9
If you build with treated lumber, line the inside with heavy-duty plastic sheeting
Plant vegetables at least 12 in (30 cm) from the inner edge of a treated-wood frame for extra protection. Line the bottom of the bed with 1/4 in (6 mm) hardware cloth to keep out burrowing rodents. Under the bed, black landscape fabric or plain cardboard blocks weeds while still letting water drain through. Skip black plastic sheeting as an underlayment, since it does not let water through and can cause root rot.
- Step 10
Do not fill a deep bed with native soil or plain fill dirt, since it packs down hard over time
Instead, mix in organic matter along with a material such as coconut coir that keeps the soil draining well. Aim for a fill mix with the texture of a premium potting soil. A typical mix runs about two-thirds to one-half topsoil combined with one-half to one-third plant-based compost. Keep added compost to roughly 10 to 20 percent of the bed's total soil volume. Plan on needing about 6 to 7 cu yd (4.6-5.4 m³) of fill material for every 1,000 sq ft (93 m²) of bed. Fill the bed all the way to the top of the frame.
Mistakes to avoid
Do not use native soil or fill dirt in a deeper bed, since it will become very dense and compacted. One of the more common mistakes with beds 18 inches or deeper is using un-amended soil with inadequate drainage. The deeper the bed, the greater the need for good drainage. Black plastic sheeting under the bed is not water permeable and will cause root rot. Colored, printed cardboard may leach printing chemicals into the soil. Railroad ties and pressure-treated lumber purchased before 2004 should stay out of an edible bed. Wood that has been dipped in preservative, rather than pressure-treated, is not usually recommended for contact with the ground. A bed wider than 4 feet is hard to work, since most people can only comfortably reach 2 feet to the center. Boards longer than 6 feet are more likely to warp or break. Beds longer than 6 feet or taller than about 18 inches need cross cable or anchored stakes. Keep added compost to about 10 to 20 percent of the bed's total soil volume. Tall beds also need more frequent watering.
How this page was made
- Written with AI assistance from the sources listed on this page. AI is never the source of a fact.