How to Build a Raised Garden Bed — Materials, Soil Mix & Cost

A raised garden bed can be built in a single afternoon and produces vegetables for 10–20 years. This guide covers lumber selection, soil volume calculations, the best soil mix, and everything you need from hardware store to harvest.

Soil volume by bed size

Bed size	Depth	Cubic feet	Cubic yards	40 lb bags
4×4 ft	6 in	8	0.30	12
4×4 ft	12 in	16	0.59	24
4×8 ft	6 in	16	0.59	24
4×8 ft	12 in	32	1.19	48
4×12 ft	12 in	48	1.78	72
4×8 ft	18 in	48	1.78	72

40 lb bag of garden soil ≈ 0.67 cu ft. For bulk orders, 1 cu yd = 27 cu ft.

Lumber materials (standard 4×8 bed, 12 in tall)

Material	Quantity	Approx. cost
2×6×8 ft cedar boards	4 boards	$60–$100
2×6×4 ft cedar boards	4 boards	$30–$60
Corner posts (4×4×12 in)	4 pieces	$20–$40
3 in exterior screws (box)	1 box	$8–$15
Cardboard (free)	1 layer	$0
Landscape fabric (optional)	32 sq ft	$8–$15
Soil mix (see below)	1.2 cu yd	$80–$200
Total		$206–$430

Best soil mix recipe

For 1 cubic yard of raised bed mix:

0.6 cu yd (60%) topsoil — provides minerals and weight
0.3 cu yd (30%) compost — feeds plants, improves drainage
0.1 cu yd (10%) perlite or coarse sand — prevents compaction

This mix drains well, holds nutrients, and stays loose season after season. Add 2 inches of compost on top each spring.

Build steps

Step 1 — Choose your site

Full sun (6+ hours/day) is ideal for most vegetables. Level ground makes construction easier. Keep it near a water source.

Step 2 — Cut and assemble the frame

For a 4×8 bed: two 8-ft boards for the long sides, two 4-ft boards for the short sides. Stack two boards high for 12-inch depth. Screw boards to corner posts with 3-in exterior screws.

Step 3 — Position and level

Set the frame in place. Check with a level. Use a rubber mallet to adjust corner posts into the ground for stability.

Step 4 — Line the bottom

Lay cardboard inside (overlapping seams by 6 inches) to kill weeds. Wet the cardboard thoroughly.

Step 5 — Fill with soil mix

Add soil in layers, tamping lightly. Leave 2 inches from the top to allow for watering and mulch. Water thoroughly after filling.

Step 6 — Mulch the top

Add 2–3 inches of straw or wood chip mulch between plants to retain moisture and suppress weeds within the bed.

Best vegetables for raised beds

Vegetable	Min depth	Spacing
Lettuce, herbs	6 in	4–6 in
Beans, peppers	12 in	6–12 in
Tomatoes	18 in	18–24 in
Carrots, beets	12 in	3–4 in
Squash, cucumbers	12 in	18–24 in

Frequently Asked Questions

How much soil do I need to fill a raised bed?

A 4×8 ft raised bed at 12 inches deep needs 32 cubic feet — about 1.2 cubic yards. Use a mix of 60% topsoil, 30% compost, and 10% perlite or coarse sand. For a 4×4 bed at 12 inches: 0.6 cubic yards.

What wood should I use for a raised garden bed?

Cedar and redwood are the top choices — both are naturally rot-resistant and last 15–20 years without treatment. Douglas fir is cheaper and lasts 5–7 years. Avoid pressure-treated lumber near vegetables; if you must use it, choose ACQ-treated wood (arsenic-free).

How deep should a raised garden bed be?

Minimum 6 inches for flowers and lettuce. 12 inches is ideal for most vegetables. 18 inches for deep-rooted crops like tomatoes, carrots, and squash. Taller beds (24 in) reduce bending and are good for accessibility.

Should I put cardboard at the bottom of a raised bed?

Yes — a layer of cardboard (remove tape and staples) at the bottom smothers grass and weeds beneath the bed and breaks down into organic matter within a season. It also keeps soil from washing out through the gaps.

What is the best soil mix for a raised bed?

Mel's Mix (from the book Square Foot Gardening) is widely recommended: 1/3 vermiculite, 1/3 blended compost, 1/3 peat moss. A simpler alternative: 60% topsoil, 30% compost, 10% perlite. Never fill with 100% native soil — it compacts and drains poorly.

How to Build a Raised Garden Bed — Complete Project Guide