Building raised beds for your vegetable (or herb, or flower) garden requires an investment of work plus the cost of materials, but they will reward you in the coming years in a number of ways. Raised beds are usually built out of lumber, but a wide variety of other materials can be used, from bricks and stones to recycled plastic sheets. The premise is simply to contain the soil within some sort of frame that holds the soil above ground level. Whether you’re starting your garden for the first time this spring, or expanding an established plot, it’s worth considering the following benefits of raised beds.
The soil in raised beds warms faster in the spring, and stays warmer in the fall, allowing you to extend your harvest period. Because the soil is elevated above ground, drainage is also improved. Keeping the beds relatively small (not more than 4 feet wide) means that you can access the whole bed from either side, so you never have to tread on the soil within – this means you can keep the soil fluffy and loose. This type of soil is good for all plants, but particularly useful for growing carrots and other root vegetables.
Raised beds also produce an environment that is easy to control. You can decide exactly what kind of soil and amendments go into each one, and you can even vary the nature of the soil to suit the kind of plants you intend to grow. “Lasagna gardening” is particularly easy in raised beds, as you are continuously building the soil “up” from ground level. Similarly, Square Foot Gardening is a breeze because you’ve got a very contained area to start with.
Building a number of raised beds makes crop rotation in the small garden a very simple matter. With each passing season, you an alternate your crops so that they never grow in the same soil two years in a row. This can help to prevent insect pests, and some soil diseases from become established. And if you don’t want to rotate your crops from place to place in the garden (because of sunlight needs, for instance), you can rotate the soil, itself, from box to box. Be sure to add lime to at least one of your beds each year as you rotate your crops.
Because raised beds are essentially just frames full of soil, you can take advantage of their construction in several ways. It’s very easy to make an instant cloche greenhouse out of a raised bed, for instance, by securing cloche pipe in place with U-brackets fixed to the inside or outside of the box. What an ideal place to grow tomatoes!
By building a separate frame out of 2×2” beams, the same dimensions as your raised bed, and stapling clear plastic onto it, you can create an instant cold frame, which is perfect for germinating seeds earlier in the spring. This same frame can also have mesh screen attached in order to keep birds, cats, or other animals out of the boxes. Lightweight row cover will offer protection from insects if used in the same way, and heavyweight row cover can be used to protect plants from frost. The same frame can be adapted to hold black plastic in place when the beds are not in use, which will prevent weed seeds from germinating, and shade cloth can be used in the summer to slow the bolting of lettuce and spinach plants.
If all of these benefits were not enough to convince you, consider the fact that raised beds can also be placed just about anywhere. You can build them straight in the middle of a lawn area in your yard. One of our customers even built some in his dedicated parking stall at work! The ability to build your soil above ground means that tilling compacted soil is not necessary. Converting sod into workable garden space is half of the problem in new gardens, so raised beds are a great alternative.
When you’re first designing your raised beds, try to build them as tall and as sturdy as your budget allows. Using cedar shingles for the sides is a good idea, as it decomposes very slowly. For food gardening, be sure to avoid lumber that has been pressure treated, or treated with chemicals. It’s smart to bring in new soil to fill your raised beds if you can find quality soil at a garden centre. Obviously, the larger the beds you build, the more soil you’ll need to fill them, and this is an important consideration when planning your budget. Large quantities of new soil can be expensive, but it’s a worthy investment, as you’ll be using it for many years. It simply forms the basis from which to work forward.
Once again, “lasagna gardening” is made really easy in raised beds. You can start by pulling out blocks of sod from between the beds, and laying these, grass-side-down on the bottom layer of the beds. Mulched bark or gravel can then be laid in between the beds as a low-maintenance path system. Build up from the bottom of the bed with layers of new garden soil, newspaper or cardboard, peat moss, barn litter, rotted manure, compost, leaves, wood ash, grass clippings, Sea Soil, glacial rock dust, well-rinsed kelp, and straw. This will build the perfect environment for soil organisms to get to work converting all that organic matter into healthy, nutrient-rich soil.
You don’t need to fill raised beds right to the top, either. In fact, leaving 4-6” empty at the top will create a slight windbreak for the soil, and will help to raise the soil temperature faster each morning.
Part of the problem with giving specific instructions on building a raised bed is that there are so many variables – the dimensions of the bed and the kind of lumber you choose make all the difference. But here is a plan for the sake of example only. The goal is to create a 2 foot tall bed that is 8 feet long and 4 feet wide. Eight feet is a common length for lumber to come pre-cut from home building centres. Most of these building centres can cut lumber up for you. You will need a total of nine 1″ x 8″ cedar fencing planks. Ask the lumber yard to cut three of these nine pieces in half – these will be your 4′ end pieces. Then you will need one 8′ length of 2″ x 2″ lumber. The type of wood is less important for this piece. Ask the lumber yard to cut this into four 24″ pieces. Finally, you will need at least 48 screws. Ask for 2″ galvanized wood screws. These will not rust. The only tool you will need is a drill for screwing in the screws.
The construction concept is relatively simple. All the boards “stack” on one another and are screwed into the 2″ x 2″ sections like so:
The screws can be alternately spaced close to each other and farther apart, so they don’t hit each other within the 2″ x 2″ piece. This is a very basic raised bed construction, and there are masses of ways to achieve the same goal.
To answer Terri’s (very reasonable) question: Lime is incorporated in crop rotation. We talk about this on page 20 of our print catalogue. Lime “sweetens” soil by adjusting the pH to a neutral point. Different families of plants respond better to different soil pH levels. And soil tends to become slightly more acidic from year to year. You can take advantage of this natural tendency in raised beds.
Assume you have three raised beds side by side.
Year one, you apply lime to the first bed in spring, and plant lettuce, spinach and the Brassicas (cabbage, kale, broccoli).
Year two, you don’t apply lime to bed one, but you plant peas, beans, onions, squash, flowers, or buckwheat.
By year three, the soil in bed #1 will be relatively acidic, so plant acid-loving crops like root crops, tomatoes, potatoes, and peppers.
So each year, one of your three beds will get limed, and the crop rotation follows so that you always have the right pH for the right groups of vegetables. This way, you’re never growing the same crop in the same spot from year to year. This is a good way to avoid pests and diseases that might otherwise set up shop if you plant the same crop year after year in the same spot.
As far as how much lime to apply, please just follow directions on the bag or box it comes in. Our Dolomite Lime comes in a 2kg box (ZFL346A) that covers 10m².