Raised or in-ground beds—which are best for growing food and flowers?
Cleaner soil and easier plantings are just two reasons why many gardeners are building beds above ground level
For most, the traditional image of a garden includes a rectangular patch of flat ground with vegetables lined up in rows, or flower borders surrounding a lawn. Raised beds—enclosed boxes of soil crammed with flowers or vegetables growing above ground-level—might not immediately come to mind, but they are becoming increasingly common and are often the most appropriate way to garden in many settings. The question: which method is best for you?
Each has its place
Of these two choices, there is no absolute right or wrong, but some situations make one or the other more suitable. Traditional gardens are the best choice for:
Very large crops of flowers, herbs, or vegetables. Average home gardens have traditionally been about ten-by-twenty feet, and that amount of produce can easily grow in a few raised beds planted intensively. But if the planted area is 20,000 square feet or more, that’s a whole lot of raised beds to build, plant, manage, and harvest. A large in-ground planting is better.
Grasses, grains, or legumes. Grain is the harvested seed of grasses such as oats, wheat, rye, millet, or rice. Legumes are plants that fix nitrogen in the soil, such as soybeans, peas, chickpeas, and alfalfa. In all these cases, you need lots of space.
Pumpkins, winter squash (sprawling vines), or corn. Squash vines need many square feet of space, and a successful corn planting also calls for a couple hundred square feet to be worth doing.
Easier and cheaper gardening. Generally, in-ground plantings are cheaper; building enclosed raised beds usually requires some purchase of materials and strenuous work to assemble.
Raised beds are best for
Compacted, depleted, or polluted soil. In many urban settings, the soil has been abused, depending on what the property was used for in the past. Testing is complex, as many labs are reluctant to say how much of any pollutant is too much, and it’s difficult to decide what to test for. Rather than risk contamination, it’s often best to build up.
Poor drainage. Elevated beds dry out sooner in spring and faster after a rain.
Accessibility issues. For anyone with limited flexibility or strength, a raised bed makes gardening possible. The beds should have sides at least two feet high, with seats at the ends or corners. It then becomes a pleasure to sit and reach out to plant, weed, or harvest, or simply to be near enough to touch or smell the plants.
Earlier plantings. Raised beds warm up quicker, and lend themselves well to cold frames or row covers to extend the growing season.
Contained, small gardens. A small raised bed is another form of container gardening, which serves urban gardeners or other busy people well.
Raised bed materials
Consider the choices:
• Rocks, bricks, pavers, or cinderblocks (open end up)
• Straw bales: ideal in that they slowly decompose and contribute organic matter to the soil
• Wattle: a creative, pretty choice if you have materials and skill
• Sand bags: heavy and durable
• Fabric beds such as the Smart Pot Big Bag beds: many sizes and shapes, lightweight
• Recycled plastic, usually HDPE (High-density polyethylene): durable and non-leaching, commonly made from milk jugs
• Wood, both logs and planks (be sure that logs are not harboring a known pest)
The other way to raise it
Organic farming and gardening require systems for protecting soil, building soil, preventing and managing weeds (without herbicides), deterring diseases and pest insects (without pesticides), maintaining productivity (without synthetic fertilizers), and using space efficiently. These systems usually comprise wide rows, intensive planting, biodiverse planting, permanent paths (to keep people and equipment off the soil), and some kind of raised beds. These raised beds are contained and only slightly elevated above the ground.
A raised bed without walls has most raised-bed benefits without building anything. It protects and maintains the soil—no compaction, easier weeding, and good use of space.
1. Prepare the soil. Usually that means adding compost, manure, or decomposing organic matter such as leaf mold. Put minimum weight on the soil; turn over lightly, enough to break the soil surface; do not till thoroughly.
2. Measure and mark beds and paths. Beds should be three or four feet wide (depending upon the gardener’s reach), and paths about twenty inches (or wider to accommodate wheelbarrow or carts).
3. Use a shovel, hoe, or rake to move soil off the paths and onto the beds. Aim for beds to be several inches above the paths.
4. Rake the top of the beds level.
5. Level the paths and line with either straw, wood chips, sawdust, pea gravel, or boards. If drainage is adequate, some gardeners prefer clover or grass paths.
Always remember: Gardening starts with good soil, whether the beds are raised or level.
Wood is the most common product for raised beds, but we’ve learned lots about our choices in recent decades. When I wrote about raised bed growing in 1996, in Great Garden Companions, many people were using railroad ties, telephone poles, and pressure-treated wood. But warnings about toxic chemicals were traveling through organic gardening circles. What we learned:
Railroad ties and telephone poles use wood that was soaked in creosote as a preservative. Creosote is basically a soup of toxic chemicals that persist in soil, and many have been proven to be carcinogenic.
Pressure-treated wood seemed to be the answer for long-lasting raised beds, well into the 1990s. It was preserved with chromated copper arsenate (CCA), a chemical banned by the EPA in 2003 when the agency concluded that CCA leached into the soil, contaminated plants, and presented health risks.
New versions of pressure-treated wood are now available that use copper and a fungicide but no arsenic, which seems safer, but has not been sufficiently tested.
Natural wood is a good choice. Master craftsman Craig Vogel has used rough-cut hemlock planks, two inches thick, for raised beds. Those eight by four-foot rectangles last for at least a decade and then gently decompose. Vogel also recommends white oak, larch, Douglas fir, or black locust for beds in the WNY area. (Some gardeners travel to Amish country to find sawyers to provide roughcut lumber.) Cedar is especially good for building raised beds because it’s soft—therefore easy to work with—but also has natural resistance to rot.
Tips for wooden raised bed success
SUPPORT THE PLANKS
For boards less than two inches thick, pound support posts, such as rebar or two by two stakes, into the ground every three or four feet outside the boards to prevent buckling.
DELAY THE DECAY
When using woods that are prone to rot, line the inside walls of the bed (not the floor) with heavy-duty builders’ plastic. It’s not exactly organic, but it can make a bed last a long time.
USE PREMADE CORNERS
Noncarpenters will find these helpful in adding a creative touch (many are attractive) and making the process easier.