Raised Bed Gardening: How to Plant and Care for Raised Beds

A raised bed earns its keep through the soil inside it: loose, never stepped on, quick to warm in spring and fast to drain. Everything about planting and caring for one follows from protecting that soil. Keep the bed narrow enough to reach across, fill it with a blended mix, plant in tight blocks rather than rows, and replace what breaks down each year.

The same features bring trade-offs. A raised bed dries out faster than ground soil, so it needs water more often than a row garden, and close planting with limited rotation raises the risk of leaf disease and soilborne problems.

Site, size and soil

A productive bed sits in full sun, stays narrow enough to tend from the path and holds topsoil and compost blended together. Vegetables need 6 hours or more of direct sun, and crops grown for their fruit want 6 to 8. A spot you pass every day, within reach of a hose, makes watering and pest checks easy.

Make the bed 3 to 4 feet (90 to 120 cm) across if you can reach in from both sides. Against a fence or wall, where you work from one side, keep it to about 2.5 to 3 feet (75 to 90 cm). Never stand on the soil, because every footstep packs it down. Paths need only 1 foot (30 cm) for walking, but a wheelbarrow or cart needs 2 to 3 feet (60 to 90 cm).

For vegetables on open ground, 8 to 12 inches (20 to 30 cm) of soil in the frame is plenty. Most crops root at least 6 to 12 inches deep (15 to 30 cm) and do better with more. Any bed with less than 12 inches (30 cm) of soil therefore needs an open bottom over loosened ground that roots can grow into. On a patio or other hard surface, where roots cannot go deeper, allow at least 10 inches (25 cm), and more for some crops.

Height beyond that is mainly about access. A gardener who works from a wheelchair needs walls from 24 inches (60 cm) up to about 32 inches (81 cm), set to suit the person, around a bed about 3 feet (90 cm) wide. For anyone who simply finds bending hard, 1 to 3 feet (30 to 90 cm) of height helps.

Fill the frame with loam or sandy-loam topsoil and plant-based compost, roughly one-half to two-thirds topsoil, blended before it goes in. Wherever one material sits on top of another, water hangs at the line between them and roots are slow to cross it, so fork the bottom few inches of fill into the loosened ground as well. Potting mix on its own dries out too fast in a bed, and a fill made largely of compost or manure dries fast, sheds water when dry and loads the soil with phosphorus and salts.

Test the new fill before planting and every 2 to 3 years after, aiming for pH 6.0 to 6.5. Lime works slowly, so if a test calls for it, spread it in fall or several months before planting. Frames, lumber, the base of the bed and soil quantities are covered in how to build a raised garden bed, and cedar raised garden beds compares the rot-resistant woods.

Plant in blocks, not rows

Set plants in blocks, just far enough apart that they will not crowd each other at full size, because a bed nobody walks on needs no space between rows. Close planting gives more produce per square foot, and the leaf cover shades the soil so fewer weed seeds sprout.

Intensive planting distances for beds. Use the wider figure for larger varieties and where leaf diseases have been a problem.

Square-foot planting. This method marks a bed no more than 4 feet (1.2 m) across into 1-foot (30 cm) squares and fills each square with as many plants as their mature size allows. Small crops pack in tightly: 16 carrots, radishes or onions per square at 3 inches (8 cm) apart, and 9 beets, bush beans or spinach plants at 4 inches (10 cm). A pepper gets a whole square to itself.

Go vertical. Climbing crops use far less soil when they grow upward. Run a trellis along the north side of the bed so its shade falls behind the bed rather than across shorter crops. Cucumbers and pole beans both climb well; see how to build a cucumber trellis for heights and post depths.

Crops that cost the most room. A summer squash claims about 2 feet (60 cm) each way, winter squash and melons sprawl unless trained up a trellis, and sweet corn pollinates well only in a block of several short rows. Many gardeners grow these in the ground and keep beds for compact crops.

A sample 4 x 8 bed

One 4 x 8 foot (1.2 x 2.4 m) bed, planted this way, can supply most of the vegetables one or two people eat over the growing season. The plan below fills all 32 square feet (3 m²) at a late-spring planting, with the long sides running east to west so the trellis stands on the north edge.

Counts follow the spacing table and the square-foot figures: 3 in (8 cm) for carrots, onions and radishes, 4 in (10 cm) for beets and bush beans, 6 in (15 cm) for leaf lettuce. Radishes and lettuce finish first, so resow or replant those squares as they empty.

Keep every square foot working

Succession planting. Group crops by how long they take to mature, so a whole patch comes free at once. When spring lettuce or radishes finish, the space can go to beans, cucumbers or another warm-season crop. You can also resow the same crop at intervals, or plant varieties with different days to maturity, to spread the harvest. Seedlings started in trays 4 to 5 weeks ahead let you fill a gap the day it opens, and many spring crops do even better sown again for fall.

Interplanting. Pair a quick crop with a slow one: radishes sown between young peppers come out before the peppers need the room. Onions can fill the gaps between tomatoes or peppers the same way, and shade-tolerant lettuce or spinach will grow in the shadow of taller beans. Choose partners with similar light, water and feeding needs.

Water, mulch and feed

Water whenever the soil is dry 2 to 4 inches (5 to 10 cm) down, mulch once the soil has warmed, and feed by soil test. Raised beds warm faster in spring and lose water faster in summer than ground beds, and the taller the bed, the faster it dries.

Watering. In weeks without rain, a bed needs 1 inch (2.5 cm) of water or more, which soaks about 12 inches (30 cm) into well-drained soil and wets the root zone of a typical bed. In its first year the mix drains fast enough to need as much as 2 inches (5 cm) a week; in a hot spell, a bed may need water every other day. The mix holds more as its organic matter breaks down.

Drip and soaker lines. Lay them on the soil about 2 to 3 feet apart (60 to 90 cm), put them on a timer, and run them until the whole bed is moist. They keep the leaves dry, while overhead sprinklers wet the foliage and spread disease. Trellised crops dry out faster than sprawling ones, so check them first in hot weather.

Mulch. After the soil warms, mulch around young plants with straw, shredded leaves or fine bark, 2 to 4 inches deep (5 to 10 cm). Organic mulch holds in water, keeps the soil cooler in summer and smothers weeds; laid too early, it keeps spring soil cold and slows warm-season crops. Pine straw and bark may lower pH slightly over years, which a routine soil test will catch.

Feeding. Where a soil test shows medium phosphorus and potassium, scratch a half cup of 13-13-13 into each 4 x 4 foot (1.2 x 1.2 m) area at planting. That is 1 cup for a 4 x 8 bed, and long-season crops get a smaller second dose of about 1/3 cup per 4 x 4 area a few weeks on. A fill made with slow-release fertilizer mixed through it, like the potting mixes nurseries use, feeds the bed for its first few months. After that, switch to a fertilizer high in nitrogen and potassium but low in phosphorus, such as 15-0-15, at the same 1/3-cup rate.

Side-dressing. Crops that must keep growing fast, such as sweet corn, squash and beans, need extra nitrogen halfway to harvest: scratch about a level tablespoon of high-nitrogen fertilizer into the soil beside each plant or hill. Long-season tomatoes and okra need two or three of these doses a season, and sandy fills or very wet weather call for more frequent ones. Too much nitrogen grows leaves at the expense of fruit, so let the soil test, not habit, set anything beyond this.

Rotation, pests and disease

Rotate crop families among your beds, keep burrowing animals out from below, and water at the soil to hold leaf diseases back. Growing the same families in the same few beds year after year raises the pressure from soilborne diseases and nematodes.

Rotation. Keep each crop family out of a bed for 3 to 4 years. For the tomato family, that covers tomatoes, peppers, eggplant, potatoes and tomatillos. Following a heavy feeder such as broccoli with peas or beans, which add nitrogen to the soil, helps too. Several smaller beds, rather than one big one, make that rotation workable.

Nematodes. A bed or container lifted off the ground and filled with clean mix helps you avoid nematode trouble, as long as no garden soil is mixed in. A bottomless bed gives less protection, because its roots grow on into the native soil, and replanting the same families there lets nematodes build up.

Burrowing animals. Mesh laid across the whole footprint stops them from below. Pocket gophers need hardware cloth or poultry wire with a 3/4-inch (19 mm) mesh, voles need 1/4-inch (6 mm) mesh or smaller, and hardware cloth also keeps out mice and chipmunks. Galvanized or stainless wire lasts longer underground. In a bed that is already full, the mesh can go in only after you empty it.

Birds, rabbits and weeds. Bird netting over the bed keeps birds off seedlings and fruit, and netting or a fence keeps out rabbits. Keep the grass around the bed mowed and the weeds pulled, since both shelter insects and compete with the plants along the edges.

Leaf disease. Crowded plants hold humid air around their leaves, which favors many diseases. Water at the base of the plants and give the largest crops the wider spacing in the table.

Through the year

A raised bed needs a small job each season: top it up in spring, mulch and harvest in summer, clear it in fall and keep it covered over winter.

Spring. Add 1 to 2 inches (2.5 to 5 cm) of blended mix to replace what broke down over the past year, and retest the soil if it has been 2 to 3 years. Black plastic over the soil warms it where straw would keep it cool, and with a row cover on top, a bed can often be planted up to 2 weeks earlier than an ordinary garden. Hoops covered with spun-bonded row cover or plastic, or a cold frame, let you start frost-tolerant greens earlier still. The vegetable planting calendar gives dates by frost for your area.

Summer. Keep the mulch topped up, keep pace with watering through hot spells, harvest often and replant each gap as it opens.

Fall. Pull spent plants. Healthy ones can be turned into the soil to add organic matter, but send any that had leaf spots, blight or mold out with the trash or to municipal compost rather than digging them in. Fungi such as early blight and septoria leaf spot survive the winter on infected debris left in the garden. Row covers and cold frames carry cool-season crops later into fall and early winter.

Winter. Never leave the soil bare over winter. Spread shredded leaves, pine straw or compost about 2 inches (5 cm) deep over an empty bed, or sow a cover crop such as winter rye. The cover crop adds organic matter and nutrients and is turned under in spring.

To map a rotation across several beds, draw them to scale, paths included, in Sow's garden design studio.

When a bed is not working

Match the symptom to its cause before you add fertilizer or water; these are the problems that show up once a bed is planted.

Problems that appear once a bed is planted, with the likely cause and the remedy for each.