If you’re getting ready to install a raised bed garden or just thinking about the possibility, there are a few things worth considering before you start. Like any building project, your raised beds require investment and planning. You want to get things right the first time to save unnecessary costs and headaches. After decades of working with raised gardens, we recommend considering the following questions.
1. How do you decide where to put your raised beds?
Before you decide where to locate your bed, think about what you hope to grow. Most vegetables need at least six hours of sunlight each day–and more is often better. Leafier plants like Swiss chard, lettuce, and spinach will grow with less than six hours of sunlight, or some dappled shade throughout the day, but their growth will be slower. Other crops need all that sunlight to thrive.
Once you’ve established what you want to grow, choose a spot for your beds based on the hours of sunlight needed. You can figure this out with a sunlight calculator or a cell phone app like Sunseeker or Lumos. In most cases, orienting your beds east to west–and planting tall plants at the back–means your crops won’t be in the shade of anything next to them.
2. What type of soil do you need?
Raised garden beds are elevated off the ground. For this reason, using a more absorbent soil mix to help retain water and nutrients is important. Absorbent materials could include anything from coconut coir (which can be costly for large beds) to finished compost (which is more affordable and full of nutrients).
Whatever you use, make sure the blend is from sources that contain a high percentage of organic matter. Topsoil mixed with compost and peat moss is a common blend. You can amend the soil with more specific minerals and nutrients based on what you plan to grow. For more information, read 3 Soil Mixes for Raised Garden Beds.
3. What plants grow best in raised gardens?
As long as you have six hours of full sunlight, you can grow almost anything in your raised beds. Root vegetables, leafy crops, peas and beans attached to a trellis…these will all do well in a raised garden. The important thing to consider is soil depth, since different plants have different needs (see below).
4. How deep should you build your raised beds?
If the soil beneath your raised beds is fertile enough to grow on its own, you won’t need to raise your garden more than twelve inches. That’s because plant roots will have access to a foot or so of nutrients below bed level.
If your soil is marginal, or you’re installing your beds on concrete, you’ll need to go higher–up to three feet in some cases. What you want to grow will affect your bed’s finished height, since different plants have different needs. Deep rooting crops like tomatoes, sweet potatoes, squash, asparagus, and watermelons do best with 24 to 36 inches of depth. For more details on soil depth requirements, see our guide.
5. What size should raised beds be?
Assuming we’re talking about rectangular raised beds, the length and width is dependent on a few factors.
The easiest way to gauge bed width is to measure your arm from shoulder to fingertips. If your bed will be accessible from both sides, you can double the length of your arm and subtract 6 to 8 inches. That’s about how far you can reach comfortably. This means you’ll end up with beds somewhere between 3 and 4 feet.
Length is another matter. Long beds with minimal paths make irrigation easier, but you want something that isn’t too cumbersome to navigate. Popular lengths include 6, 8, and 10 feet.
6. Do you need cross-bracing?
Cross bracing is useful for longer, wider beds, because the pressure from the soil can cause a bed to bow outwards. This is somewhat dependent on the thickness of your boards, but in general, a bed six feet or longer will benefit from cross bracing.
You can attach a piece of wood across your bed above or below soil level or you can use stainless or galvanized steel.
7. What's the best way to fasten the corners?
Corners are the weak point on raised garden beds. In the winter, when the soil freezes and expands, corners take the brunt of the pressure. There are a number of different ways to reinforce your corners to give your beds the longest life possible.
Stakes driven into the ground at the four corners provide a handy place to nail horizontal boards in a DIY wooden bed.They can extend into the ground about a foot.
Corner brackets provide a quick way to fasten and reinforce your beds at the same time. They are perfect for DIY raised bed construction. Some corner brackets come with anchors that feature a stake that can be hammered into the ground. Others stack on top of one another to stabilize multiple tiers. The key when buying corner brackets for DIY beds is to make sure they’re designed for the same thickness as your lumber.
External trim added to your bed after it has been built will reinforce the corners and seams and add a finished look to your garden. Raised beds trimmed at the corners and seams will last longer.
8. What's the best material for raised bed gardening?
Popular materials for raised beds include wood, plastic, aluminum and galvanized metal. Wooden frames are more prone to changing shape in areas where cycles of freezing and thawing occur, but corner reinforcements and cross bracing usually eliminate this problem. Plus, wooden frames are easy to build yourself. You can accommodate tiered or sloping ground quite easily with wooden beds.
The best wood for raised garden beds includes cedar, cypress, redwood, or white oak. Availability will vary by region, so be sure to find out if the wood at your local store is long-lasting and rot resistant. Avoid repurposing old, treated lumber which may contain chemicals that have since been banned for home use. Ensure any new treated lumber is certified as safe for growing food. As the cost of wood rises, it is becoming more cost effective to purchase raised bed kits. Cedar is a long-lasting and rot resistant wood commonly used in raised bed gardening.
Metal beds are another popular choice, although some, like wooden beds, can weather over time. Aluminum is very long lasting, though acid in the soil can erode a galvanized metal bed’s zinc coating, exposing the metal to rust. Thankfully this process takes several decades and galvanized metal beds can last up to twenty-five years or more.
Composite raised beds are also available. These are made from a blend of eco-friendly, recycled plastic and wood flour. Purchase complete kits or individual boards for a DIY, modular set-up.
For the longest lasting bed, consider those made from 100% recycled high-density polyethylene (HDPE). This is the same material used to make public picnic tables, litter bins and high-quality garden furniture. HDPE plastic withstands a wide range of temperatures. It will not leech any chemicals into your garden soil. Some varieties are so long lasting, they come with a 50-year warranty.
9. Do raised beds need a bottom?
This all depends on the surface where you plan to put your garden. Most raised beds don’t have bottoms. That’s because beds without bottoms give your plant roots more growing depth and better drainage. However, if you’re planting on a surface with invasive weeds or concrete, you might choose to install a bottom on your bed to block weeds or prevent staining.
If you have burrowing pests in your region, adding a wire mesh bottom to your bed will help thwart any damage from these unwanted visitors.
10. How should you irrigate?
Installing irrigation in a raised bed will save you time and money. Drip irrigation is the most eco-friendly and cost effective over the long term, particularly if you have too many beds to water by hand. It delivers moisture slowly over time, losing very little to evaporation. If you plan to garden in the same location for many years, drip irrigation is the answer.
If you’re not sure how long you’ll use your beds, or if you’re working on a tighter budget, soaker hoses can be a great solution. Choose a material that is toxin-free and durable (like this FDA grade polyurethane soaker hose with lead-free fittings) or a double-walled variety to avoid kinks. Lay it down the length of your bed and keep free from mulch and soil that may clog pores. Use a water timer on soaker hoses and drip irrigation to save water and make life easier.
Related: Drip Irrigation vs. Soaker Hoses-Which is Best for Your Garden?
11. What's the best way to protect your crops?
If you live in an area where animals frequent the neighborhood, a fence is the best way to protect your garden. Deer and rabbits munch, raccoons and cats dig, even dogs will excavate beds to get at some types of fertilizer. A fence provides the best and longest lasting protection. Obviously the fence will need to encircle your garden’s perimeter, but the height will depend on the pests in your area. For more information, read How to Keep Deer Out of Your Garden.
12. What fertilizers should you use and when?
Finished compost is the best amendment for your raised beds, hands down. That’s because compost includes essential minerals and nutrients that plants need, along with lots of organic matter to improve soil structure. Add compost when you prepare your soil for the year, to each row or planting hole, and again as a top dressing or mulch mid-way through the season. Some crops, such as corn, squash, and tomatoes benefit from more frequent additions.
If you plan to grow plants in the brassica family (broccoli, cauliflower, kale, cabbage, mustard greens, etc.), you may need to add lime to your soil before the growing season starts. To be sure, check your soil pH using a home-test meter. Avoid planting potatoes, peppers and tomatoes in beds that have been recently limed.
Raised bed gardening success
Taking the time to carefully plan your garden means you’re less likely to need drastic changes once you’re growing. With careful consideration and foresight, the only change you’ll need is more beds.
