A raised bed is the most forgiving way to start a garden. You control the soil, the drainage, and the layout. But the dimensions you choose on day one affect everything that follows: how many plants fit, how easy it is to reach, and how much soil you need to buy.
The golden rule: reach from both sides
Never build a raised bed wider than you can comfortably reach to the center. For most adults, that means:
- 4 feet wide if accessible from both sides (the standard)
- 3 feet wide if you have shorter arms or limited mobility
- 2 feet wide if the bed is against a wall or fence (accessible from one side only)
Length is flexible. Common lengths are 4, 6, 8, or 12 feet. Longer beds need internal bracing if the walls are thin, or the soil pressure will bow them outward.
Common bed sizes
- 4×4 feet (16 sq ft) — great first bed. Fits 16 square-foot planting squares. Enough for a salad garden: lettuce, herbs, radishes, and a few tomato plants.
- 4×8 feet (32 sq ft) — the workhorse. Room for a diverse mix of vegetables with proper spacing. Two of these feed a couple through summer.
- 4×12 feet (48 sq ft) — serious production. You can dedicate sections to crop families and rotate annually. Needs sturdy construction.
Depth matters
The soil depth determines what you can grow:
- 6 inches — minimum for lettuce, herbs, and shallow-rooted greens. Only works if there is plantable ground underneath.
- 10-12 inches — the standard. Accommodates most vegetables including tomatoes, peppers, and root crops like carrots. Works on any surface, including concrete or compacted clay.
- 18-24 inches — table height or deep beds for accessibility. Also good for deep root crops like parsnips or daikon radish. Requires significantly more soil.
For beds placed on existing soil, roots will grow down into the ground below, so even a 6-inch bed can grow deep-rooted crops. For beds on hard surfaces, 12 inches is the minimum for serious vegetable gardening.
Spacing between beds
Leave enough room to walk, kneel, and wheel a barrow between beds:
- 18-24 inches — tight but walkable. Fine for small gardens.
- 30-36 inches — comfortable. Room to kneel beside the bed without blocking the path.
- 48 inches — allows a wheelbarrow or garden cart to pass. Essential for larger gardens where you move soil, compost, or harvests in bulk.
Soil mix
The classic raised bed mix is equal parts by volume:
- Topsoil — provides mineral content and structure.
- Compost — provides nutrients and microbial life. Aged compost, not fresh.
- Coarse material — perlite, vermiculite, or aged bark fines for drainage and aeration.
A 4×8 bed at 12 inches deep needs roughly 32 cubic feet of mix, which is just over 1 cubic yard. Buying soil in bulk (by the cubic yard from a landscape supplier) is dramatically cheaper than bags.
Materials
- Cedar or redwood — naturally rot-resistant, lasts 10-15 years. The premium choice.
- Douglas fir or pine — affordable, lasts 3-5 years untreated. Line the inside with plastic sheeting to extend life.
- Galvanized steel — corrugated metal panels. Lasts 20+ years, heats up in sun (which warms soil earlier in spring but can stress roots in summer).
- Concrete blocks — cheap, permanent, easy to stack. The cavities can be planted with herbs.
- Stone or brick — beautiful, permanent, expensive. Best for formal gardens.
Avoid pressure-treated lumber from before 2004 (contained arsenic). Modern pressure-treated wood uses copper-based preservatives and is considered safe for vegetable gardens by most extension services, though some gardeners still prefer untreated wood.
Orientation
Run beds north-to-south when possible. This gives both sides of the bed equal sun exposure throughout the day. Plant tall crops (tomatoes, corn, trellised beans) on the north end so they do not shade shorter crops to the south.
If your yard slopes, run beds along the contour (perpendicular to the slope) to prevent soil erosion and water runoff.
Planning your layout
Before you build, sketch your layout on paper or in a planner. Account for:
- Sun exposure (minimum 6 hours of direct sun for vegetables)
- Water access (where is your hose bib or rain barrel?)
- Path widths between beds
- Room for trellises and supports on the north side
- Future expansion (leave space to add beds later)