How To Keep Dirt From Draining Under Garden Boxes

Of course, you don't need a raised bed to grow great-tasting produce—most any plot of flat ground that gets full sun will suffice for that. But gardening in a raised bed offers a number of advantages. For one thing, there's less bending over, so it's easier on your back. Build the sides high enough and you can even garden while sitting.

Raised-Bed Gardens

Raised beds also allow you to start fresh with enriched, uncontaminated soil-; on sloped property, they offer level, easy-to-tend planting areas. And because these beds warm up faster in the spring than those at ground level, you get a head start on the growing season.

But all those advantages won't help if you neglect the soil, and according to sustainable-living expert Greg Seaman, that's the mistake most beginners make. Seaman, who shares his gardening know-how online at Eartheasy.com, has been growing vegetables in raised beds for nearly 40 years. "When the soil is rich in organic matter and nutrients, plants are more robust and virtually take care of themselves," he says. "There's less weeding, less watering, and fewer pests."

Here we provide practical advice about the types of frame materials and mulches to use, ways to enhance soil fertility, and the various options for irrigating. Plus, we offer strategies for deterring insects (and other invaders). In short, we show you all you need to know to get started as a raised-bed gardener.

Shown: To make optimal use of the space in these raised beds, use tall teepee trellises to provide sturdy supports for pole beans.

Before You Start

HOW MUCH DOES A RAISED BED COST? A simple 4-by-8-foot cedar frame built from scratch or a kit generally runs just over $100. A 4-by-8-foot brick-sided bed built by a mason will cost about $2,000. Plan on spending about $3 per cubic foot for bagged garden soil.
DIY OR HIRE A PRO? Wood-framed beds and kits are easy to build, even for a beginning DIYer. In most cases, the hardest part is preparing the soil under the bed and filling the frame. You'll probably need a pro to erect a bed made of mortared masonry.
WHERE TO PUT IT? Choose a spot that gets at least 8 hours of sun a day, and orient each bed so its long side runs east to west. Keep beds at least 6 feet from pavement and south-facing walls, which intensify summer heat.
HOW LONG DO BEDS LAST? That depends on what they're made of. Beds built with western red cedar can last 10 to 15 years; galvanized steel, 20 years; masonry or plastic composites, indefinitely.

Shown: TOH landscape contractor Roger Cook helps a homeowner build a frame out of 2x western red cedar, a naturally rot-resistant wood well suited for this purpose. He advises against using preservative-treated boards or creosote-soaked railroad ties, which can leach chemicals that contaminate soil.

Build a Raised Garden Bed from Scratch or a Kit

Both are viable options, but if you're looking for out-of-the-ordinary materials, kits ease the process.

Until fairly recently, about the only way to get a raised bed was to buy some boards, cut them to size, and screw them together yourself. Or you could hire a mason to build one for you out of brick or stone. The only limits were your imagination and budget.

But these days, you can find a growing assortment of all-inclusive raised-bed kits with precut parts that save time, eliminate guesswork, and offer a variety of looks. They may not have the one-of-a-kind uniqueness of scratch- or pro-built beds, but they come in a wide array of striking materials—including wood, steel, composite boards, and tumbled concrete blocks—that can add a handsome accent to any landscape.

Shown: These kit-built beds have porous, rot-proof sides made of wood chips and cement. They're held in place by aluminum corners coated with a tough, baked-on finish and are capped with western red cedar.

From $298; Durable GreenBed

How Big Should a Raised Bed Be?

WIDTH: Four feet across is considered ideal, so you can comfortably reach the center from either of the long sides.
LENGTH: A bed can be any length, as long as the sides are supported every 3 to 4 feet to resist the soil's outward pressure. Either drive 2x stakes next to the sides or attach the ends of wood or metal strapping to opposite sides of the bed.
HEIGHT: Low beds are less work to construct and fill, but require double digging to prep soil beneath the bed. High beds mean less digging and less stooping, but need more soil and building materials. Eleven inches is a common height: that's two 2x6s stacked on edge.

How deep to make it?

Tender herbs can grow in 6 or 8 inches of soil, but many vegetable roots go much deeper. Make room for them by building a high- sided bed or double-digging below grade (or both). As you dig, amend the top 10 inches of under-bed soil with peat moss or coconut coir. This organic matter helps retain water in sandy soil and improve drainage in clay soils.

ROOT DEPTHS

12–18 inches: Lettuce, potatoes, radishes, strawberries
18–24 inches: Carrots, peas, beans, cucumbers, peppers
24–36 inches: Tomatoes, rhubarb, asparagus, artichokes

Choose Your Material: Wood

There's more than one way to build a bed frame.

Readily available and easy to cut, it's the most commonly used material for raised-bed frames. For maximum longevity, use thick boards cut from rot-resistant species, like this 1½ inch-thick Port Orford cedar.

Shown: 48-by-96-by-11-inch Rectangle kit, $295; Naturalyards

Choose Your Material

Steel

It's stiff and strong and usually given a galvanized or painted finish to stave off rust. This bed, made of lightweight corrugated steel, has a colorful powder coating.

Shown: 34-by-68-by-12-inch Demeter kit, $90; Gardener's Supply

Mortared Masonry

This type of bed will last nearly forever with minimal maintenance, but requires a concrete footing poured below the frost line and someone with bricklaying skills to build it. Weep holes every 2 feet or so in the base course let water drain out. Expect to pay about $2,000 for a 4-by-8-by-2-foot brick bed similar to this one.

Stacked Stone

Fitted together and held in place with dabs of construction adhesive, natural stone or look-alike cast-concrete blocks don't need mortar or a footing, just a tamped crushed-stone base. Line the bed with landscape fabric so water can drain without carrying away soil.

Shown: 49-by-49-by-10 ½ inch RumbleStone concrete-block raised-bed kit, $273; Home Depot

PVC

Hollow vinyl planks won't rot or rust, are lighter and more flexible than wood, and help insulate the bed from rapid temperature changes, but they do get brittle with age. If you want another color, you can apply a heat-reflective paint. These food-grade planks are BPA- and phthalate-free.

Shown: 48-by-48-by-11-inch Raised Garden kit, $90; Vita

Composite Lumber

Usually a blend of plastic and wood fiber, these boards are more resilient than vinyl, and last longer than wood. Just make sure they're rated for ground contact.

Shown: 48-by-96-by-11-inch Classic Sienna kit, $200; Frame It All

The Secrets of Great Soil

TO START: Mix equal parts compost with peat moss (or coconut coir) and vermiculite (or perlite). Or blend compost 50-50 with topsoil or bagged garden soil. If you want an organic bed from the start, buy bagged soils and compost that are OMRI-Listed; they've been certified by the Organic Materials Review Institute. Note: Soil that doesn't meet organic standards can be considered organic after three years if not treated with herbicides, pesticides, or synthetic fertilizers during that time.

IN THE FALL: Pull up and compost any spent plant material, and cover the soil with a thick layer of ground-up leaves (just run over them with a mower). Hold them in place with netting so they don't blow away. Or plant seeds for a thick cover crop of alfalfa, buckwheat, white clover, or annual ryegrass. Do this 30 to 60 days before the first frost so the seeds have time to germinate.

IN THE SPRING: About a month before planting, chop the leaf material or cover crop into bits with a spade or hoe and blend it gently into the soil. Before you plant rooted seedlings, fertilize each planting hole with a few trowelfuls of compost, a scoop of composted manure, and ½ cup of rock phosphate or blood meal.

Shown: Fill the bed right to the top with soil; it will soon settle a few inches, leaving a lip to hold in the mulch.

Design the Corners of Your Garden Bed

Low Profile

With prefab connectors, you can quickly build beds with your choice of wood or composite planks. Just slide them into the connector grooves, and screw into place, as needed.

Rigid powder-coated aluminum brackets from 8 to 35 inches tall form sturdy corners for a range of bed heights. Matching in-line extrusions are available to connect side walls.

Shown: Lifetime Corners, from $25 per pair, screws included; Gardener's Supply

Four Sided

This wood-plastic composite corner has grooves on all sides to join corners and side walls, and even to link up with other beds, no screws required. When stacked, they're held together with rebar driven through their center holes.

Shown: Oldcastle Planter Wall Block, $3.50; Home Depot

Hinged

These ABS plastic brackets pivot 270 degrees, allowing you to build beds in interesting, non-rectangular shapes. To stack them, simply insert the built-in stake into the bracket below; slot in boards and secure with screws.

Shown: Stacking Bracket, $15; Frame It All

Why Does Mulch Matter?

The right top layer-—about 3 inches thick—discourages weeds, retains moisture, adds nutrients, and keeps the soil where it belongs.

Use these to improve the soil:

STRAW OR HAY: Straw (harvested grain stalks) stays put, doesn't mat, and insulates the soil. Hay (alfalfa or a grass) breaks down faster, enriching the soil; but avoid the fresh stuff used for animal feed—it contains weed seeds. Instead, spread salt hay (a marsh grass) or old feed hay that has started to decay; their seeds won't sprout.
FALLEN LEAVES: Another boon to soil fertility, if you can find enough of them in the spring. Grinding them up first makes them less likely to mat and helps them break down faster.
GRASS CLIPPINGS: They're high in nitrogen and break down quickly, but apply them just 1 inch thick to prevent matting. In late summer, use only dried clippings—they won't stimulate unneeded growth, as fresh ones will. But don't use them at all if your lawn is being treated with herbicides or pesticides.
SEAWEED: Rinsed of salt, this nutrient-rich material contains no weed seeds, acts as a natural fertilizer, and, once dry, stops slugs. Kelp isn't a good mulch, but does make a fine fertilizer tea.

Avoid these:

WOOD CHIPS: They're slow to degrade and, if mixed into soil, will acidify and starve it of nitrogen. Put them on paths between beds.
SAWDUST: This fine waste forms a water-impenetrable mat and, as with wood chips, can have a negative effect on soil fertility.

Shown: Straw mulch keeps leaves and produce clean and dry.

Keep Beds Hydrated

Sprinklers can waste half the water they emit. These efficient systems deliver it right to the roots, where it's needed most.

Soaker hose: At about 40 cents per foot, it's the least expensive, least complicated watering option. Just lay it in the bed, and hold it in place with landscape staples. Thread on a pressure regulator set to 15 psi for spray-free operation, and connect it to a hose bib with a backflow preventer. Most soakers are made from recycled tires; Water Right's food-grade, BPA-free polyurethane hose is a welcome exception ($55 for 25 feet; Water Right).
Drip tape: Flat tubing made of polyethylene—a plastic similar to that in milk jugs—comes in various widths, wall thicknesses, and drip-hole spacing. A 15-mil-thick tape will last longest, about 7 ½ years; 5⁄8-inch-wide tapes with holes every 12 inches are suitable for most beds. These tapes only go in straight runs; a rigid manifold at one end of the bed feeds water to each tape.Use a pressure regulator set to 15 psi or less to prevent bursting. $49 for 100-foot kit; Dripdepot
Drip line: The most efficient and longest-lasting irrigation option, it's also the most expensive ($76 for 50-foot kit; Dripdepot). Plastic fittings allow the thick-walled polyethylene tubing to follow any path you choose without a manifold, and the tubes can be fitted with drip emitters to send water precisely where it's needed. Quarter-inch lines are limited to 30-foot runs; ½-inch lines can go up to 200 feet. Both work best at 25 psi.
Irrigation controller: A battery-powered timer like the Aquauno Logica ($49; Dripdepot) lets you set the timing, frequency, and duration of waterings. An add-on sensor suspends the schedule if it rains. More expensive electronic controllers, like the Rachio 3 ($230; Rachio), automatically regulate watering based on local forecasts, and enable you to use your smartphone to monitor water use and initiate watering.

Shown: Drip tape irrigates in straight runs.

Damage Control: Tree Roots

How to deal with creeping, crawly, and furry invaders that can decimate a garden.

Stop them from sucking up moisture and nutrients by digging a 2-foot-deep trench around the bed and lining it with corrugated plastic panels. Overlap panel edges by 6 inches and seal them with polyurethane adhesive and stainless sheet-metal screws. Leave the panels' top edge exposed so roots can't grow over it.

Keep Out Slugs

These garden pests won't touch copper—it gives their slimy bodies a shock. A strip of copper flashing wrapped around the outside of beds can keep slugs out. Crispy seaweed mulch or a sprinkling of coffee grounds also repel them. Or patrol beds an hour before sunrise or an hour after dark to pick them off plants by hand.

Keep Out Aphids

Add companion plants such as marigolds, nasturtiums, and petunias to vegetable beds to repel these little suckers. These plants emit compounds that discourage all kinds of damaging insects—including whiteflies, cabbage loopers, and squash bugs—from munching away in your garden.

Keep Out Rabbits & Woodchucks

Enclose your vegetable garden with a fence at least 3 feet tall and 3 feet from your beds. To stop critters from chewing through or digging under it, line it with 4-foot-wide, ½-inch galvanized hardware cloth buried 1 foot deep—even under the gate. Rig the gate to close automatically, and make sure it has no gaps wider than an inch.

Keep Deer Out

They can't dig under or chew through a fence, but they can jump it. Plastic netting at least 8 feet high hung around the garden perimeter will keep deer from bounding over. A slanted 8-wire fence, like that sold by Gallagher, is only 4 ½ feet high but 6 feet deep. It works because deer can jump high or far, but not both.

Extend the Growing Season

To protect tender plants from cold snaps in spring and fall, place a cloche, or small tent, over the bed. You can buy a kit or build your own out of ½-inch PVC pipe, 1x lumber, and UV-treated 6-mil plastic sheeting. Be sure to lift the plastic on sunny days, or provide a vent at the peak on each end so heat can escape. Remove the tent entirely when the danger of frost is past. For step-by-step cloche-building instructions, visit the Oregon State University Extension Service.

Give Peas (and Beans) a Chance

A grid-style trellis attached to a raised bed provides the support that peas and beans need as they climb toward the sun. Mount the trellis on the bed's north side, so it doesn't shade the other plants, and leave enough space between the strings or wires—at least 5 inches—so you can reach in and harvest the ripe pods from the back side.

Raised-Bed Inspiration: Canoe-Shaped

Smart, stylish ideas for elevating your garden.

Flat, smooth capstones offer a welcome place to sit when weeding and harvesting in this custom stone bed. Expect to pay upwards of $8,000 for a 12-by-4-by-2-foot bed in a similar shape in quartzite.

Tip: Before building or setting a raised bed in place, make sure—by excavating, if necessary—that it will be resting on level ground. Otherwise, the soil in the bed will shift to the bed's low end and may spill out over the top.

Raised Garden Bed Inspiration

Ochre Rounds

These curved metal planters are made of weathering steel, an alloy that corrodes only on the surface for a warm rusty finish.

Similar to shown: 30-by-10-inch Custom Corten Round Planter, $800; Scott Avidon Design

Keyhole Bed

The 20-inch-high walls of this U-shaped, western red cedar kit-built bed put plants within easy reach. An add-on fence raises the outside to a deer-discouraging 67 inches tall and doubles as a trellis support.

Shown: 8-by-8-foot Raised Garden-Bed Kit with Deer Fence, $1,849; Outdoor Living Today

Formal Finish

The solid stain on these custom frames makes a pleasing contrast with the pea-gravel pathways. To minimize upkeep, make the sides out of rot-proof 5⁄4x10 cellular PVC trim, the rails from clear 5⁄4x4 cedar decking, and use 4x4 cedar posts for the corners, topping them with ball finials cast from polyurethane foam.

Materials cost for a 4-by-12-foot bed similar to shown: about $375

Exposed Joinery

Just stick the side-board tenons through the mortises in the ends; black locust pegs hold the boards together. You can stack the finished frames as high as you like. Made of white cedar, these boards weather to a soft gray.

Shown: two of The Farmstead's 24-by-72-by-8-inch raised garden bed kits, $100 each; Garden Raised Beds

Built-In Benches

Narrow edges don't make for comfortable seating. Here, wood benches are fastened to the bed's sides, offering a perch for tending vegetables or taking in the view. Each 2-foot-long seat can be built from an 8-foot length of 26 western red cedar for about $20.