Experienced gardeners use raisedbeds to sidestep a long list of gardening challenges. These controlled experiments in plant parenthood are so easy, in fact, that they're also well-suited to novices picking up a shovel for the first time.
Bad dirt is out, because you fill a raised bed with a customized soil-and-compost blend. Drainage is built into the bed walls, which hold the soil in place to keep erosion in check. Greater exposure to the sun warms the bed, which allows more plant diversity and extends the growing season. Plants can be spaced closely together, so yields go up, water-use efficiency is maximized and weeds are crowded out. Finally, raising the soil level by even a foot reduces the back-bending effort needed for jobs such as planting, weeding and harvesting.
Beyond the ease is the control—as you grow your favorite foods, you feed and soak your plants with just what they need for optimum growth.
A raised bed is most productive and attractive as a bottomless frame set into a shallow trench. The sides can be almost any durable building material, including rock, brick, concrete and interlocking blocks. Watering troughs or claw-foot tubs can work, as long as they have the capacity and drainage.
But by far the most common material for raised beds is lumber. The major caveat, since raised beds are often used to grow edibles, is to steer clear of wood preserved with toxins. Avoid creosote-treated railroad ties; opt instead for naturally rot-resistant cedar or redwood. The EPA considers wood infused with alkaline copper quaternary (ACQ) to be safe for food crops, but if you use this pressure-treated wood you may want to line the bed interior with landscape fabric—an air-and-water-permeable screen—to prevent soil contact. Whether using pressure-treated or naturally rot-resistant wood, put the bed together with galvanized or stainless screws or bolts.
A 3 x 6-ft bed should be wide enough to support sprawling tomatoes, but narrow enough to reach easily from both sides. The ideal height is 1 to 2 ft tall—you can go taller, but you need a considerable amount of soil to fill a 3-ft-high bed. Don't fill the bed with dirt from the garden. Instead, use peat moss, compost or a soil mix for planters. Use a 2 x 4 to level the soil, then plant. If possible, build more than one bed, which makes it easier to rotate crops and meet the watering needs of specific plants. Aligning beds in straight rows simplifies the installation of an irrigation system.
Finding a flat spot spares a lot of digging—you want the walls to be level. In general, a north-south orientation takes full advantage of available light. Stay close to the kitchen, but avoid sites shaded by the house or beneath messy trees. Leave at least 18 in. betweenbeds for walkways, or 2 ft if you need room for a wheelbarrow or lawnmower.
To prepare the site, get rid of turf and weeds. Outline the bed dimensions on the ground with chalkline or string, then dig with vertical strokes along the outline, just deep enough to bury about half of your first course of lumber. Raised beds are designed so water trickles down, eliminating most of the problem of poor drainage. But if your only viable location is bogged in a marsh, you can prevent the "bathtub effect" by digging a few inches deeper and putting a layer of coarse stone or pea gravel in the excavation. (You can also install perforated drainage pipes in trenches under or around the bed, or just drill weep holes at the base of the sides.) Likewise, if there is no turf between your beds, put down some landscape fabric and cover it with pavers or a layer of gravel to improve drainage—after running out in the rain for a fresh bell pepper, you'll appreciate the mud-free shoes.
Level the earth or gravel layer at the bottom of the bed, then put down a layer of weed-suppressing landscape fabric that extends to the outer edge of the wooden frame. Now is also the time to think about pest control. "The rich soil in a raised bed has worms and other delicacies that attract moles, and gophers and voles relish young veggie roots," Sausalito, Calif., garden designer Tom Wilhite says. "To keep out burrowing pests I always recommend a bottom layer of hardware cloth"—a mesh grid of steel or galvanized metal.
Build each wall separately, then fasten them together and put the bed into position. Raised-bed builders often sink posts into the ground for stability, either at the inside corners of the bed or halfway along the side walls. These hel
p hold the bed in place, but can also reduce the outward pressure that a full bed exerts on the frame, which can dislodge the lumber after a single season. A cap railing that runs around the top of the bed ties everything together. Plus, it provides a handy place to set down gardening tools while working, or, when you're done, a seat to admire the fruits of your labor. Bed covers ward off insects and keep plants warm in cool weather.
A simple framework of hoops and a lightweight cover can extend your growing season in cool areas, conserve moisture in dry areas and protect plants from birds or insects. Use galvanized pipe straps to mount 1-in. PVC pipe inside the bed walls. Cut ½-in. flexible PVC tubing twice as long as the beds' width. Bend it, mount it and clip a cover in place. Use clear polyethylene film to raise soil and air temperatures in early spring or fall—to get an early start on heirloom tomatoes, for instance, or to try your hand at exotic squashes. But be careful not to bake your plants on warmer days. Remove the cover or slit vents in it to avoid excessive heat buildup. For pest control, cover the bed with bird netting or with gauzelike fabrics known as floating row covers, which keep out flying insects but let in both light and air.
Once you add an automatic watering system to your raised-bed garden, you're free to plant, weed and harvest. A simple micro-irrigation setup ensures that plants get water consistently—especially important for seedlings and leaf crops such as lettuce. "The sides of raised beds heat up quickly in the sun, baking the moisture out of the soil," Wilhite says. "Irrigation delivers the water evenly and gently. You can set your timer to water early in the morning—less will evaporate, and you resist disease."
A basic setup starts with a faucet or hose-bib attachment that is essentially a series of valves that prevent back flow into the plumbing, filter the water and control the water pressure.
These valves are designed with 1-in. or ¾-in. connections. From these, attach supply lines of flexible ½-in. poly tubing. The tubing's accessibility makes it easy to check for leaks and repair damage from punctures or bursts. To protect the tubing, bury it a few inches and cover the line with mulch.
Lay the tubing along the beds in lines 12 in. apart. Fit sections together with compression elbow and T-fittings. Install drip emitters at 12-in. intervals along the length of the tubing for even delivery of moisture to plants. Low-volume sprayers or misters on risers can also be used, but these lose more water to evaporation. Close the ends of each line with hose-end plugs and caps. Then sit back and let the system water for you.