Control weeds and pests so you can enjoy a longer veggie-growing season.
Choosing a size
Raised beds come in all shapes and sizes. They're completely customizable depending on the gardener's specific requirements. However, these measurements are considered standard for a typical raised bed.
Length and width
The standard length and width of a typical backyard raised bed is about 3 to 4 feet wide by 6 to 8 feet long. This allows for easy access from all sides when you're planting and weeding. It's best to be able to reach into the beds from the side when you're working in them.
Technically, if you want to build one long raised bed, that's narrow in width (because that's what your space allows), you could do that, too, but you must be mindful of the fact that the sides can shift if you don't add supports every few feet.
Staking the side of a raised bed: the ground around your raised bed will shift and heave over time—especially after a rough winter. While it may be tempting to simply create a standard raised bed rectangle with stakes attached to the inside corners, over time you may find the middle of the longest lengths warping out or in, or shifting. One way to avoid this problem is to secure stakes to the outside of the raised bed, about halfway from the end, at the time of building. This should keep the boards firmly in place.
The height of a raised bed can vary greatly. Generally, though, raised beds are a bit lower to the ground. A standard rule of thumb is to make them about 10 to 12 inches high. However, if your beds are really low and you're planting carrots, parsnips, or other root vegetables, for example, the plants are going to reach down into the subsoil that's beneath the raised bed. If the root vegetables hit the uncompromising soil underneath, they can become stunted and misshapen. Even plants that grow upward will have roots that travel downward, and they may hit the subsoil underneath. If that soil isn't healthy, or it's hard and compacted, it's going to affect the plants. There are measures you can take to amend the subsoil, such as double-digging and adding compost. But if you don't want to have to deal with the subsoil, simply increase the height of the bed a few more inches so your crops will be contained in the raised bed.
If you're upcycling an old container into a raised bed, make sure that the depth will allow for the roots of your chosen plants to flourish. A lettuce table, for example, is very shallow, so it's only suited to plants with equally shallow root systems. Deeper raised beds allow for all other edibles to be planted and to thrive.
The distance between your raised beds is also important. There should be enough space so that you can comfortably bend or kneel down to access the raised beds from the sides. If you'll need to maneuver a wheelbarrow between beds, you'll need to take that into consideration as well.
Choosing raised bed materials
Just as the soil you choose is an integral element to creating a raised bed, so are the materials with which you choose to make them.
For wooden raised beds, look for untreated, rot-resistant wood. The availability of certain woods at the lumberyard or home improvement center will depend on your location and what grows in your region. However, it's likely that the most common rot-resistant wood you'll find is cedar. Even most of the raised bed kits that you can order online come with cedar boards. Before loading up your cart with wood, be sure to check the price per board so you know how much your raised bed is going to cost. You don't want to be surprised with a budget-busting tab when you get to the checkout.
Look for the Forest Stewardship Council (FSC) stamp when you're purchasing your wood. It's an international certification and labeling system with standards that tracks where your wood has come from and promotes responsible forest management. When you purchase wood with an FSC label, you know it has come from a reputable source and has been properly harvested.
When you're building a bed with rot-resistant wood, the hope is that it will last several years before you have to replace rotting lumber. Some boards will unfortunately age faster than others.
Lining a bed with plastic can help prevent wood from rotting. The lining keeps the wet soil from touching the wood on the inside. Just be sure to only line the sides of the raised bed and not the bottom because the water needs to drain downward and out the bottom of the bed. To avoid rusting, you'll also want to use stainless-steel staples to fasten the plastic or landscape fabric to the bed.
Be careful when you're reusing wood that's come from another project. For example, you want to avoid using railroad ties and pressure-treated wood—especially if you're growing edibles—because the harmful chemicals they were treated with can leach into the soil: Until about 2003 or 2004, chromated copper arsenate (CCA) was used in the making of pressure-treated wood.
Because of past practices, current opinions vary on using the new pressure-treated woods that are on the market. You may want to investigate these materials for yourself and decide what you're comfortable using for your raised beds.
If you're reusing old wood that has an old coat of paint on it, you need to be careful because the paint could contain lead.
Even if your raised beds are built from rot-resistant wood, they'll still deteriorate over time, and you may need to replace boards here and there. If you want to help prolong the life of your raised beds, you can treat the wood using an ecofriendly stain, although you may still want to confine its use to the outside boards if you're growing food in the bed. Some wood oils use natural ingredients and offer UV protection. Flaxseed oil and wax are natural stains that can be used to protect the wood. Be wary of linseed oil, however; it can contain chemical additives that you don't want around your plants. Do a little research to find a sealer that you feel comfortable using for your raised beds.
Some materials will simply last longer than wood. Old paving stones or bricks can be piled to create raised bed walls. Just be mindful of using a technique that ensures they're not going to cave in. As you would with old wood, if you're reusing concrete blocks, for example, be sure you know where they come from. Concrete blocks used to be called "cinder blocks" and were made with fly ash, which is a dangerous substance.
Make sure that whatever material you choose for your raised bed isn't going to leach dangerous chemicals into your soil over time. For example, one safe option is to have a professional weld steel into sturdy raised beds that will truly stand the test of time.
Excerpted from Raised Bed Revolution (Cool Springs Press) by Tara Nolan, $36. ©2016. All rights reserved.