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How to build a 3x8 raised garden bed

A 3 × 8 ft raised bed you reach from both sides, from six 8-foot 2 × 6 boards, a 6-foot 4 × 4 and 40 screws, with the cut list, the steps and the soil it takes.

11 in8 ft outside
The finished bed, drawn to scale beside an adult 5 ft 6 in tall: 8 ft × 3 ft outside, 11 in tall, filled 10 in deep with 12 bags of 1.5 ft³ soil.

Build it

96 in
1. Each long side: 2 boards of 96 in, 3 posts, the end ones 1½ inches in from the ends.
33 in end boards
2. Stand the sides up and fit the 33-inch end boards between them, into the corner posts.
96 × 36 in outside, 11 in tall
3. Square it, set it level and fill 10 in deep: 17.3 ft³, 12 bags of 1.5 ft³.
  1. Choose a level spot and mark a 96 × 36 inch rectangle. Keep a path along both long sides.
  2. Cut two of the 2 × 6 boards into four 33-inch end boards, two from each, and cut the 4 × 4 into six 11-inch posts. Check each cut with the square.
  3. Build each long side: lay two 96-inch boards flat, edge to edge. Place a post on them 1½ inches in from each end, leaving room for the end boards, and one post centered at 48 inches. Drive two screws through each board into each post, 12 screws per side.
  4. Stand the two long sides up, posts facing in, so the boards are 33 inches apart on the inside.
  5. Fit two 33-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, 16 screws in all.
  6. Measure both diagonals from corner to corner on the outside. They should both be about 102½ inches; push the frame until they match, then check it is level.
  7. 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.
  8. Set the bed in place and fill it.

How much soil it takes

Filled 10 inches deep, the inside of this bed takes 17.3 cubic feet of soil once the posts are taken out: 0.6 cubic yards, or 12 bags of 1.5 cubic feet. That leaves an inch at the top of the 11-inch walls for mulch, and it is three quarters of what the 4 × 8 plan takes (16 bags).

Open this bed in the soil calculator to change the depth or split the soil into a mix. It counts the full 93 × 33 inches with the posts left in, so it shows 17.8 cubic feet; the bag count stays at 12.

Once it is filled, open its 93 × 33 inches in the planting planner to see what fits: it starts from a salad bed you can change. The 3 × 8 planting layouts are drawn for a full 3 × 8 feet inside, so this bed holds a little less of each crop: 14 heads of lettuce across the whole bed rather than 24.

Pricing it? The build or buy calculator sets this plan’s list against a kit you could buy instead, soil included, at the prices you are quoted.

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.

Try it with your numbers

Open the raised bed soil calculator with this guide’s bed filled in, then change any figure to match yours.

Open the raised bed soil calculator

References