Guides · Landscaping
How to Build a Raised Garden Bed (and Fill It Right)
By the MyBuildCalcHub team · Figures verified against our audited estimating engine · Updated
Choosing size and height
Two dimensions decide how well a raised bed works. Width should never exceed 4 feet, because you garden from the sides and need to reach the center without stepping in and compacting the soil, a 4-foot bed gives two feet of reach from each side. Length is free; 8 feet is popular only because lumber comes in 8-foot lengths. Height is really about root depth and back comfort: 6 to 8 inches suits salad greens, 10 to 12 inches is the versatile default for most vegetables, and 18 inches or more spares your back and lets deep-rooted crops thrive. If the bed sits on open, healthy soil, roots reach below the frame for bonus depth.
Building the frame
The frame is simple carpentry. Choose a naturally rot-resistant, untreated wood, cedar and redwood are the classics, or a composite if budget allows; avoid old-style treated lumber near food crops. Butt the corners and screw into a vertical corner post (a length of 4×4) for a joint that survives years of wet soil, use exterior screws, and level the frame carefully on cleared ground, since a bed that's out of level drains and waters unevenly. That's genuinely the whole build, the craft in a raised bed isn't the woodworking, it's what you fill it with.
Filling it: the volume and the blend
Getting the fill right the first time saves a season of disappointment. Start with volume: a bed is length × width × height, converted to cubic yards by dividing cubic feet by 27. The blend that decades of growers have settled on:
| Component | Share | For a 1 yd³ (4×8×10 in) bed |
|---|---|---|
| Topsoil | 60% | ~16 ft³ |
| Compost | 30% | ~8 ft³ |
| Aeration (perlite, coarse bark) | 10% | ~3 ft³ |
That 4×8 bed with 10-inch sides holds about 27 cubic feet, almost exactly one cubic yard, or 18 of the standard 1.5-cubic-foot bags. At that quantity, a single bulk delivery beats the bag aisle on both price and plastic.
What goes in the bottom
You do not need a solid bottom, the point of a raised bed is that roots reach the soil below. Line the base with plain cardboard or several sheets of newspaper to smother existing grass and weeds; both decompose within a season and let roots pass through. Over a hard surface like a patio, add landscape fabric so the bed still drains. For tall frames, a bottom layer of branches, leaves, and wood chips (the hugelkultur idea) fills cheap volume that slowly composts into rich matter, just plan to top the bed up as that layer settles. For the ongoing care, our mulch depth guide and raised-bed soil guide cover the yearly compost refresh that keeps a bed productive.
Where to put the bed
Placement decides the harvest before a single seed goes in. Most vegetables want at least 6 hours of direct sun a day, so track where the sun actually falls across your yard before committing, a beautifully built bed in shade grows disappointment. Leave a comfortable path between multiple beds (about 2 to 3 feet, enough for a wheelbarrow), site the bed within reach of a hose or water source since raised beds dry faster than open ground, and set it on a level spot so water soaks in evenly rather than running to one end.
Frequently asked questions
How do you build a raised garden bed?
You build a raised garden bed by assembling a bottomless frame, usually rot-resistant lumber like cedar, no wider than 4 feet so you can reach the center, then leveling it on cleared ground and filling it with a topsoil-and-compost blend. A common first bed is 4 by 8 feet and 10 to 12 inches tall.
What do you put in the bottom of a raised garden bed?
The bottom of a raised garden bed is best lined with cardboard or several layers of newspaper to smother grass and weeds, which then break down into the soil. On open ground that's all you need; over a hard surface add landscape fabric for drainage, and in tall beds a base layer of branches and leaves fills volume cheaply as it composts.
How much soil do I need for a raised bed?
A 4 by 8 foot raised bed with 10-inch sides needs about 27 cubic feet of soil, almost exactly one cubic yard, or 18 standard 1.5-cubic-foot bags. Calculate any bed as length times width times height (all in feet), then divide by 27 for cubic yards.