The best time to set up a raised-bed garden is whenever you have the time to make a garden plan and put it in action (although you can’t build a raised bed when the soil is frozen). The first step is to find the right site. Next, evaluate the soil there and decide whether to loosen it for planting or leave it intact and build a bed from the ground level up. Plan the layout of the bed or beds and what kind of frame you’ll use, if any.
The final step is deciding whether your garden will be a solo do-it-yourself project, whether you’ll enlist the help of family or friends, or whether you’ll hire some help. There’s some heavy lifting involved in the beginning phase of most raised-bed projects. But once your beds are built, tending them is generally light work for all the years that follow.
If you’re planning to convert an existing vegetable garden to raised beds, then your choice of site is already made. But if you’re starting from scratch, look for the sunniest spot you can find, because most vegetable crops grow best in bright sunshine. Lettuce and a few other crops can tolerate light shade, but the best site is one that receives at least 6 hours of direct sun per day, especially during the middle of the day.
Choose a sunny day to investigate your site. In the morning, use bricks or rocks to mark the corners of an imagined garden site; then return throughout the day to observe the sun and shade patterns. Make adjustments in the position of the bed if needed. Consider how the patterns will change over the course of the gardening season, too. In summer, the sun is high in the sky, so shadows are minimal. The sun is lower (closer to south) during spring and fall, so trees and buildings cast longer shadows that might extend across your garden site.
If your surroundings include lots of trees or buildings that block sun, your yard may offer only isolated pools of sunlight. If that’s the case, you can set up a single raised bed in each pool. There’s no rule that beds have to be grouped together. A group of beds is more convenient to tend, but sun trumps all when it comes to growing veggies and most flowering annuals — so set up beds wherever the sunlight is available. If some parts of your yard are always in shade, you can still grow many beautiful perennials there, including hostas, violas, pulmonarias, and astilbes. These will thrive in a shady raised bed.
What if you find that the sunniest site available is a driveway or patio? If you don’t mind giving up a portion of the paved area, you can work with the site by setting up a sturdy frame and filling it with a growing mix such as compost mixed with peat and sand. Be aware that the surface underneath may degrade over time. If you decide to remove the bed in the future, you may find the paved surface is pitted or stained.
Soil seems solid; after all, when you walk across a lawn or along a woodland path, you’re walking on soil, and it feels firm under your feet (unless it’s been raining hard and the soil has turned to mud). When you take a closer look at soil, though, you’ll find that it’s not solid like wood or stone. Rather, soil is made up of myriad tiny particles; bits of rock worn down through centuries become soil.
Technically speaking, there are three types of particles in soil, and they’re defined by their size. The largest group of particles is called sand, the middle group is called silt, and the smallest group is called clay. The relative proportions of these particles affect the qualities of soil: how fast it dries out, how easy it is to dig, and how well it holds nutrients that plants need for growth. For example, sandy soil dries out faster than clay soil. A soil that has a fairly even balance of all three types of particles is called loamy soil. Loamy soil can be ideal for gardening, but it’s possible to grow great plants in clay and sandy soil, too. Adding organic matter will help a lot to improve the water-holding capacity of sandy soil and to loosen up clay soil.
Once you’ve picked your site, dig a little hole to check out the soil. Scoop some soil into your hand and rub it between your fingers. A handful of soil can feel sandy, or it may feel like a loose powder (silt), or it may feel sticky (clay).
More important than these mineral particles is the living component of soil. As you dig in the soil, you’ll see some living things such as plant roots, earthworms, beetles, and centipedes. In addition, you’ll see formerly living material — dead leaves, bits of plant stem, and old roots — which gardeners call organic matter.
There’s also a universe of living organisms in the soil that you can’t see: bacteria, fungi, nematodes, and more. These living creatures are the most critical aspect of soil for gardeners. They digest nutrients in organic matter and transform them into substances that plant roots can absorb; in other words, they turn organic matter into plant food. Your work as a gardener is to provide a hospitable haven for these beneficial microbes.
If you don’t see any signs of life in your soil, that’s a cause for concern, but it’s a problem you can fix by adding organic matter in the form of compost and by mulching (covering) the soil surface with organic materials such as shredded leaves. There’s more information about improving the organic matter content of soil later in this book (see Soil Amendments).
There’s an incredible amount of life humming away in the soil, at a scale that can’t be seen by human eyes. The interactions in the soil are fascinating to learn about. And the more you discover about soil biology, the better gardener you’ll become. Here are some amazing details:
To discover more fascinating facts about what’s happening in the soil, see Resources.
Like most living things, plant roots and soil-dwelling organisms need air (specifically oxygen) in order to live and grow. That’s why soil drainage is so important. Some soils, especially those with lots of clay, don’t drain well: water tends to stay trapped in the surface soil, filling all the pore spaces, which can suffocate plant roots.
To test drainage, dig a hole at your site about 1 foot deep and 1 foot wide. Use your garden hose to fill the hole with water. Let that water drain away completely; then turn on the hose and fill the hole again. Note the time or set a timer; then check the hole now and again until all the water has drained away (it will likely take hours). If the hole isn’t empty within 8 hours, the soil drains poorly. Building a raised bed and filling it with purchased topsoil or compost is a great solution to poorly drained soil. The bed should be at least 6 inches deep to allow space for roots to grow and thrive above the heavy natural soil underneath the bed.
No soil is perfect, and while digging a hole for a drainage test, you may discover other problems, such as an abundance of rocks, very sandy soil, or a wild proliferation of persistent weed roots. The good news is that many soil problems can be lessened simply by adding organic matter. And if your site has soil with a difficult problem, you can choose simply to cover over the existing soil with cardboard or newspapers to block weed growth and build your raised garden from the ground level up.
One approach to starting raised beds involves loosening the soil and heaping it up into low mounds. The other basic bed-building method employs a solid frame constructed at ground level and filled with materials gathered off-site. Both approaches require some physical labor, and both have pros and cons. You’ll make the decision whether to dig down or build up based on the soil characteristics of your site, the type of plants already growing there, and your budget.
If your soil doesn’t have any major problems, it’s a good idea to dig down; that way, you’ll avoid the cost of buying topsoil or soil mix to fill the beds. But if your soil has a major problem, such as poor drainage or contamination by lead or other pollutants, it’s best to build frames and fill them with topsoil or compost. Building beds at least 1 foot tall offers the advantage of allowing you to tend the beds without stooping over.
Before you start digging or building frames, draw a layout plan for your garden. How many beds will there be, and what dimensions?
Start by deciding on bed width. Get down on your knees and pretend you’re reaching out with one arm to plant seeds or pick beans from a garden bed. How far can you reach without straining? For most people, the comfortable distance is 18 to 24 inches. Measure your own comfortable reach and multiply that distance by 2 — that’s the maximum bed width for your garden. (If you’re designing a bed along alongside a fence or wall, don’t multiply by 2, because your access to the bed will be limited to just one side.) A bed that exceeds your reach will lead to the temptation to step onto the bed while you work, and that negates one of the primary goals of raised-bed gardening: maintaining loose, airy soil.
Bed length is a more personal choice than bed width. It may depend on the overall shape of your garden site. For a square site, a grid of four beds may work well. For a long and narrow site, consider lining up three beds in a single row. Take care not to make beds too long, or you’ll end up frustrated by the repetitious walk around the end of the bed to get to the other side (more temptation to step onto the bed to shortcut across). If you’re a beginning gardener, it’s a good idea to start out with beds of a standard size, such as 4 feet × 8 feet.
In midsummer, when the sun is high overhead, there’s very little shade in a vegetable garden. But in spring and late summer, the sun doesn’t travel as high in the sky and tall garden crops can cast shade on the plants on their north side. Consider this when you’re deciding how to orient your beds. Should the long dimension run north to south, or east to west? Both north-south beds and east-west beds can work well, as long as you’re aware of which direction is north and plant accordingly to avoid shading crops, as shown below. Occasionally, creating shade in a vegetable garden has advantages. For example, if tall tomato plants create a lightly shaded spot, that can be a perfect place to plant a summer crop of lettuce, which benefits from some shade during peak summer heat.
Beds set up with a north-south orientation are fine for crops of equal height, but for a combination of tall and short crops, choose an east-west orientation. To prevent one crop from shading another, plant tall crops along the north edge of the bed, with shorter crops in the center and along the south edge of the bed.
As you map your layout, be generous with path width. Pathways between raised beds serve more than one purpose. They’re your workstation — the place where you will stand, sit, or kneel while you tend your garden. They’re the spot where you’ll put your bucket of work tools and supplies, and your harvest basket of produce. And they’ll be the highway and the parking spot for a wheelbarrow full of compost or transplants. Be sure your garden pathways are wide enough to accommodate all that activity. In most cases, 2 feet is the minimum comfortable width for pathways between raised beds.
