Your First Raised Bed Costs More in Dirt Than in Wood

Quick answer: Build it 4 feet wide, 8 feet long and about 11 inches tall. Fill it with roughly 60 percent screened topsoil and 40 percent compost. Plant lettuce, radishes, bush beans, basil and one tomato. Skip the zucchini and the corn this year.

Most first-timers spend a Saturday agonizing over cedar versus pine and about four minutes thinking about what goes inside. That's backwards. A 4x8 bed built from 2x12s holds about 30 cubic feet of soil. That's more than a cubic yard, or roughly twenty of those 1.5-cubic-foot bags stacked by the garden center door. The boards are the easy part. The dirt is where the money goes, and where most first beds go wrong.

Get the size right before you buy a board

Four feet wide, no wider. You need to reach the middle from either side without stepping in. The moment you step on the soil, you pack it down and undo the whole point of a raised bed. If the bed backs up against a fence, make it 3 feet wide, because you only get one side to reach from.

Eight feet long, mostly because lumber comes in 8-foot lengths and you'll make two fewer cuts. Longer is fine. Just know that walking around a 12-foot bed to get to the other side gets old by July.

About 11 inches tall. A 2x12 is actually 11 1/4 inches, and that's plenty of root room for nearly every vegetable you'll grow, especially if the ground underneath is decent. Go to 24 or 30 inches only if you've got a bad back or your native soil is solid clay or rock. But understand the trade: double the height, double the soil bill.

Leave at least 2 feet between beds, more if you'll push a wheelbarrow or a mower through. Put the bed where it gets six to eight hours of direct sun and where the hose reaches without a fight. A bed you have to drag 75 feet of hose to won't get watered in August. You know this about yourself.

If you're building from scratch, this 4x8 build comes in under two hundred dollars. Modern pressure-treated lumber is a common choice. The old arsenic-based treatment was phased out for residential use years ago. Cedar lasts longer and costs more. Either one beats a bed that never gets built.

What goes in the bottom

Lay plain cardboard over the grass, tape and labels pulled off. It smothers the turf and rots away by the time roots reach it. If you've got gophers or voles, staple galvanized hardware cloth across the bottom first. You can't add it later without emptying the bed, and you'll only learn you needed it after something eats your carrots from below.

Don't put gravel or rocks in the bottom "for drainage." It's one of the most repeated bits of garden advice and it's wrong. Water doesn't move easily from fine soil into coarse gravel, so it pools right above the rocks and sits there. You just end up with a shallower bed and soggier roots.

The soil mix, and the cheaper way to get there

The famous recipe is Mel's Mix from Square Foot Gardening: one-third compost, one-third peat moss or coconut coir, one-third vermiculite. It grows beautiful vegetables. It's also expensive to fill a full bed with, because vermiculite and coir aren't cheap by the cubic foot.

For a first bed, a simpler mix does the job: about 60 percent screened topsoil, 40 percent compost. Topsoil gives it body and holds water. Compost feeds it and keeps it loose. Mix them on a tarp or right in the bed with a shovel.

Bags or bulk? For one bed, bags are honestly fine. You'll pay more per cubic foot, but you won't pay a delivery fee, and you won't have a pile in the driveway. For two beds or more, call a local landscape supply yard. Ask for their garden mix or raised bed blend and ask what's in it. Run the numbers: there are 27 cubic feet in a yard, so compare their price per yard (plus delivery) against twenty-some bags.

Thinking of hauling it yourself? A cubic yard of wet topsoil can top a ton. Plenty of half-ton pickups have come home from the soil yard with the rear end squatting and the headlights pointed at the treetops. Check your payload rating before you pull in. Or let them deliver. Sometimes the fee is the cheapest part of the day.

The annoying part nobody mentions: some manure and compost carries residue from long-lasting herbicides sprayed on hay fields. It passes through the animal and comes out still active, and it'll curl and stunt your tomatoes and beans. The cheap insurance is to fill a couple of pots with the mix and plant a few bean seeds. If they come up twisted, with cupped leaves, take it back before it's in your bed. If you'd rather make your own going forward, compost that doesn't stink or feed the rats is easier than it sounds.

Overfill. The soil will settle several inches over the first season. Mound it a couple inches above the boards and plan to add an inch or two of compost every spring after that. A raised bed is never "done." It's topped up, like a gas tank.

What to plant first, and when

Your zone and your last frost date decide the calendar, so look both up first. Your hardiness zone decides what lives and what dies, and your local extension office can give you the average last frost date for your county. Everything below hangs off that one date.

A few weeks before last frost (cool season):

• Radishes. Ready in about a month. Sixteen to a square foot.
• Lettuce and spinach. Four lettuce plants or nine spinach per square foot. Cut outer leaves and they keep coming.
• Peas. Plant them along a trellis on the north side.

After last frost, once nights stay warm (warm season):

• One tomato. Just one. Cage it on the north end so it doesn't shade everything else. It'll take a 2x2 corner and act like it owns the place.
• Bush beans. Nine per square foot, no trellis, and a steady harvest by midsummer.
• Basil. Tuck it near the tomato. You'll use it.
• Peppers, if you have room. Compact and productive.

What to skip this year: Zucchini. One plant can swallow a quarter of a 4x8 bed and still look hungry. Corn needs to be planted in a block to pollinate, which a single bed can't give it. Pumpkins and watermelons will sprawl over the edge and across the lawn. And never put mint in the bed. You'll be pulling it out of the tomato's roots for the rest of your life.

The goal of year one isn't maximum yield. It's a bed full of things that work, so you come back next spring wanting more instead of staring at a tangle of squash leaves wondering where it went wrong.

Water is where first beds die

Raised beds drain fast and dry out faster than the ground does. Push a finger into the soil. If the top inch is dry, water deeply, until it's wet several inches down, not a quick sprinkle that wets the surface. In a hot stretch that can mean every day or two.

A soaker hose or drip line on a cheap battery timer solves most of this. So does 2 or 3 inches of straw mulch once the plants are up, which keeps the soil cooler and wetter and smothers the weeds that'll show up anyway.

If you're reading this in the fall

Build it now. Seriously. Fill it in September or October, let the winter rain and freeze settle the soil, and top it up in spring. You'll be planting radishes while your neighbor is still on hold with the soil yard.

Plant a row of garlic in fall, too. Cloves go in a few weeks before the ground freezes, sit there all winter, and come out next summer. It's the easiest win in vegetable gardening, and it means the bed's working before you've even started.

Give one square to the kids

Mark off one square foot and hand it over. Radishes are the right crop. They sprout in days and they're ready before a seven-year-old loses interest. A kid who pulls the first radish out of that bed and eats it, dirt and all, is going to ask you when you're building the second one.

Say yes. And build it 4 feet wide.