How to build a tall raised garden bed

The plan at a glance

This bed measures 96 × 48 inches on the outside and stands 22 inches tall: four 2 × 6 boards high. It is built like the 11-inch cedar bed, with posts as tall as the walls inside each corner and at the middle of each long side, and a 48-inch 2 × 4 laid across the top between the two middle posts so the long sides cannot bow outward under the soil. The inside is 93 × 45 inches.

A tall bed suits poor or compacted ground: with nothing usable below, Washington State University Extension says to build at least 15 to 18 inches deep, so the whole root zone is in the fill.

Cut list and materials

A 2 × 6 board is 1½ × 5½ inches when you buy it dry, and a 4 × 4 is 3½ × 3½ inches, the dressed sizes the American Wood Council lists. The lengths below use those sizes and allow ⅛ inch for each saw cut.

Build it

1. Choose a level spot and mark a 96 × 48 inch rectangle, with a path on both long sides.
2. Cut four of the 2 × 6 boards into eight 45-inch end boards, each 4 × 4 into three 22-inch posts, and the 2 × 4 to 48 inches.
3. Build each long side: lay four 96-inch boards flat, edge to edge. Place a post on them 1½ inches in from each end and one centered at 48 inches. Drive two screws through each board into each post, 24 screws per side.
4. Stand the two long sides up, posts facing in, so the boards are 45 inches apart on the inside.
5. Fit four 45-inch boards at each end, between the long boards and against the corner posts. Drive two screws through each end of each board into the post, 32 screws in all.
6. Measure both diagonals from corner to corner on the outside. They should both be about 107.3 inches; push the frame until they match, then check it is level.
7. Lay the 48-inch 2 × 4 across the top over the two middle posts and drive two screws down through it into each post.
8. If gophers or voles dig in your garden, fasten hardware cloth across the bottom before you set the bed down. UC IPM advises hardware cloth or ¾-inch mesh poultry wire under raised beds for gophers; Colorado State University Extension gives ¼-inch hardware cloth for voles and pocket gophers.
9. Set the bed in place and fill it, wood first if you are using it (below).

How much soil it takes

Filled 20 inches deep, leaving 2 inches at the top, the inside takes 47.6 cubic feet once the posts are taken out: 1.76 cubic yards, or 32 bags of 1.5 cubic feet. At that size a delivered load is worth a quote: the bagged vs bulk soil calculator compares them.

To buy less, lay branches and logs in the bottom 8 inches and keep at least 10 inches of mix on top; the deep-bed guide explains the settling and the nitrogen it costs. Open this bed in the soil calculator to try other depths.

Wood and screws

Use cedar heartwood and stainless steel screws, as in the 4 × 8 cedar plan, which gives the reasons; the best wood guide compares the other choices.

What this plan does not cover

This is a plan for a bed on open ground. It is not an engineered design and makes no load rating. For a bed on a patio, deck or roof, read the hard-surface guide and have the surface assessed for the filled weight first.

References

• Raised Garden Bed Dimensions (Circular 1027-4), University of Georgia Cooperative Extension
• Span Tables for Joists and Rafters, 2024 Edition, American Wood Council
• 2018 NDS Supplement, Table 1B, American Wood Council
• Wood Handbook: Wood as an Engineering Material (FPL-GTR-282), chapter 14: Biodeterioration of Wood, USDA Forest Products Laboratory
• Raised Beds: Will They Benefit Your Vegetable Garden? (FS075E), Washington State University Extension
• Fasteners for Outdoor Projects, Western Red Cedar Lumber Association
• Pocket Gophers (Pest Notes), UC Statewide IPM Program
• Vegetable Gardening in the Mountains, Colorado State University Extension