How to Plan and Build a Raised Garden Bed

Quick answer: Build a 4 ft × 8 ft × 12 in cedar bed. Fill with one-third topsoil, one-third compost, one-third aeration material. Buy soil in bulk; bagged soil costs about three times as much. Total project: about $200-300.

Pick the right size

4 feet wide is the magic number. Anything wider and you can't reach the middle from either side without standing in the bed and compacting the soil. Length is flexible: 6, 8, or 10 feet are common.

For depth, 12 inches handles almost everything. Lettuce and herbs are fine at 6-8 inches, but at that depth your bed dries out fast in summer and the roots have nowhere to go in heat. Root crops like carrots, parsnips, and daikon want 18 inches if you can swing it. If you're building one bed and want it to do double duty, 12 inches is the right call.

Use our Raised Bed Plant Spacing Calculator to figure out how many plants of each variety you can fit before you build.

Pick the material

Three reasonable options:

• Cedar. Untreated cedar lasts 10-15 years, looks great, and is the default choice. A 4x8x12 bed needs about three 8 ft 2x12 boards plus four corner posts. Budget $80-150 for lumber.
• Galvanized steel. Pre-fab steel beds (Birdies, Vego, etc.) last 20+ years and skip the carpentry. They run $200-400 for a 4x8 size and slot together in 30 minutes.
• Stone or concrete block. Permanent, attractive, expensive. Best for a yard you'll be in long-term.

Avoid pressure-treated wood from before 2003. It used arsenic-based preservatives (CCA) that leach into soil. Modern pressure-treated lumber uses safer copper-based preservatives, and the EPA considers it safe for vegetable beds, but plenty of organic gardeners still avoid it on principle. Cedar is simpler.

Choose the spot

Three things matter, in order: sunlight, water access, and convenience.

Vegetables need 6-8 hours of direct sun. Watch the area for a full day before you commit; a spot that looks sunny in the morning may be in deep shade by 2 PM. Track the worst-case shade pattern (early summer, when trees are fully leafed out).

The bed needs to be reachable with a hose. If watering is a 20-minute production, you'll do it less than you should, and the garden will fail in your first July heat wave.

Convenience is underrated. A bed you walk past every day on the way to your car will get more attention than one tucked behind the garage. Out of sight really does mean out of mind for gardens.

Prep the ground

If you're putting the bed on grass, lay down a thick layer of cardboard first — flatten cardboard boxes, overlap the seams generously, soak the whole thing with a hose. Then build your frame on top. The cardboard smothers the grass, and worms eat through it within a few months.

For weed-prone areas, double up on cardboard or add a layer of newspaper underneath. Skip plastic — it stops drainage and creates a soggy mess that kills roots.

Gopher problem? Line the bottom of the frame with 1/2-inch hardware cloth (heavy-duty wire mesh) before you fill it. Once the bed is full of soil, you can't add this later.

The soil mix

Don't fill a raised bed with regular garden topsoil. It compacts, drains poorly, and underperforms compared to a proper mix. The standard formula:

• 1/3 topsoil — your structural base.
• 1/3 compost — your nutrient and microbial source. A blend of two or three types (mushroom compost, composted manure, leaf mold) works better than one.
• 1/3 aeration material — coarse vermiculite, perlite, or pumice. This keeps the mix from compacting and improves drainage.

Mel Bartholomew's "Mel's Mix" (one-third compost, one-third peat moss or coco coir, one-third vermiculite) skips topsoil entirely and is popular in square-foot gardening circles. It works, but it's expensive and runs out of structure after a few years without amendment.

How much soil you need

A 4 ft × 8 ft × 1 ft bed holds 32 cubic feet of soil. That's:

• 1.2 cubic yards of bulk soil (yardage from a landscape supplier)
• 64 bags of 0.5 cubic-foot bagged soil from a hardware store
• About 32 bags of 1 cubic-foot bags

Bulk delivery beats bagged on cost. Bulk soil runs about $40-60 per cubic yard delivered; bagged works out to roughly $150 for the same volume by the time you've hauled 64 bags from your car. The catch: bulk delivery dumps a yard pile in your driveway and you have to wheelbarrow it from there.

Use our Garden Soil Calculator for any custom bed size, and our Mulch Calculator if you're also planning to top-dress with mulch.

The hugelkultur shortcut

If you're filling a deep bed (18+ inches) and don't want to buy 50 cubic feet of soil, fill the bottom half with branches, twigs, leaves, and other yard waste. As that material breaks down over a few years, it releases nutrients, holds water, and eventually composts down. Top with the soil mix above. This is called hugelkultur, it's been used in central Europe for centuries, and it cuts your soil bill roughly in half.

What to plant first

First-year raised beds tend to do well because the soil is fresh and the pest pressure hasn't built up yet. Easy wins:

• Lettuce, spinach, kale — quick, forgiving, productive in cool weather
• Bush beans — fix nitrogen for next year's crops, no trellising needed
• Tomatoes — need staking, but raised beds suit them well
• Peppers — slow to start but reliable producers
• Herbs — basil, parsley, cilantro all thrive in a raised bed

Skip pumpkins and watermelon for year one. They sprawl, take up enormous square footage, and you can grow far more total food per square foot with smaller plants.

The cost breakdown

For a single 4×8×12 cedar bed, expect roughly:

• Cedar lumber and hardware: $80-150
• Bulk soil mix delivered: $80-150
• Cardboard, mulch, plant labels, etc.: $20-40
• Total: $180-340

You can roughly double the budget for galvanized steel kits ($300-500 total) and roughly triple it if you only buy bagged soil.