How to Build a Raised Bed That Will Last
I’ve built raised beds out of railroad ties or cedar fencing, 2x4s, bricks, and even some nice wicker lattice. But when I got serious about not having to build new raised beds every few years, I came up with a simple, durable design that anyone can use.
This is the only way I’ve gotten around to making raised beds in the last 10 years, whether I’ve built them in the Arizona desert, the rainy Pacific Northwest, or the Georgia suburbs. This design will provide you with a cost-effective and technically simple way to quickly assemble beds for any size room. It provides more bed depth than most plans I’ve seen and requires very few tools. The durability of the beds means they won’t move over time, tilt or be damaged by your wheelbarrow.
Use the right wood
The most common mistake I see when building raised beds is choosing the wrong wood. A lot of time is often spent comparing pressure treated (PT) wood to untreated wood, or whether the wood is cedar or redwood. But the biggest problem is that people usually end up with lumber that is too thin and/or small. Fiddling with cedar pickets that are thin and flimsy, or 2x4s that don’t provide any vertical height, won’t last you long. The answer is to use larger sizes: I use 2×12 or 2×10. This means you will need fewer wood planks stacked vertically. I don’t use pressure treated wood because although the methods they currently use to treat wood are not considered toxic, I try not to introduce unnecessary chemicals into my edible garden.
While you can use any variety you like, and hardwood or cedar will certainly last longer, it is not necessary. If you use pine or redwood, these solid wood planks will last eight years or longer. When wood breaks down, it benefits your garden because it is essentially compost, and if the beds are inexpensive and easy to make, creating new ones in eight to ten years won’t seem like a burden.
Check suppliers other than big box stores.
Big box stores aren’t the only options for sourcing wood in town. Search lumber stores specifically for prices, or—my favorite trick—go to Craigslist to find independent millers selling “rough” lumber.
The advantage of independent millers (people who have their own sawmill or equipment) is that the wood will likely be cheaper and you can get a deal on all the cuts you need. Also, independent manufacturers don’t cut everything to the same length just for consistency like Home Depot does. Since they cut the wood into 2×12 pieces, if the board is 15 feet long and you only need 12, they don’t cut off the last three feet because it’s just more work and there’s no benefit to it. . The result is that you get longer discounts at the same price while supporting someone local. While I don’t consider this a flaw, this wood is typically “rough finished” – it has not been sanded to make the sides smooth. Additionally, they were not oven dried as would be the case when making a large box. store, meaning they still retain a lot of moisture. For raised bed construction, none of these issues are a problem. Raised beds will live outside with constant watering and I really don’t want smooth sides. I think it makes the beds less attractive to pests;
Determining your bed size
The raised bed is a rectangle. This rectangle can be any length; you’re only limited by the length of wood planks you can get (usually 12 or 16 feet). However, when it comes to the width of the bed, you’ll need to seriously consider making it wider than four feet (but anything in the two to four foot range will do). The reason is simple: you need to be able to reach whatever is in the middle of the bed, and anything wider than four feet makes that quite difficult. The height of the bed will always be 22 1/2 inches because we will be using two 2×12 beds stacked vertically (and once dry, the 2×12 beds are actually only 11 ½ inches tall). When designing beds, consider that the space you place them in is heavily sloped, as this may mean dividing a long bed into two so you can terrace the ground for each bed. Make sure that the distance between beds is at least three feet, but four feet is better. This will allow you to maneuver the wheelbarrow through the aisles, which will help you a lot. Don’t be afraid to grab some landscaping flags to lay out where the beds will go and just walk around, making sure everything is accessible and walkable.
Draw out the entire space, indicating the final dimensions of the beds. This will help you visualize the wood you want. For each bed, you will need one 2x12x16 lumber for the shorter sides, and then two 2×12 lumber for each of the longer sides, regardless of the length you are designing for the beds. Ideally, the boards should be slightly longer than the bed so that the ends of the boards can be trimmed.
Determine how much wood you will need
The boards you lay horizontally will need vertical supports to hold the bed together. You’ll place them at each corner and then every four feet along the long side. For a bed that is eight feet long, you will need another vertical support in the middle. A twelve-foot bed will require two additional supports. This support is just a 2×4 support that is 20 inches tall (about the same height as the beds). Add up the lengths to determine how many vertical boards you need. For example, for an eight-foot bed, you will need six 144-inch long vertical posts or a 2x4x12-foot board. For beds longer than 12 feet, I like to install additional spacers in the middle of the bed across the full width. This will help prevent the bed from sagging in the middle over time. A spreader bar is simply additional 2x12s stacked vertically across the entire width of the bed.
Tools you’ll need
The beauty of this design is that you only need very few tools. A chop saw will be useful, but a circular saw will work in a pinch. Also: power drill, wood glue, 2 ½-inch construction screws, and sander. A sander is optional. While you can make the cuts at a big box store, you’ll save a lot of money by doing it yourself, and it’s very likely that you’ll make at least one mistake when choosing the cuts you need, so being able to make the cuts where you’re building is very helpful. A sander is used to work corners to round off sharp edges. This will help prevent clothes from getting snagged or scratched when you go around the corners of beds, but it’s not necessary. Since you’ll be using construction screws, you won’t have to pre-drill anything (and the construction screws come with a suitable drill bit), but a reliable electric drill, even a hammer drill, is absolutely essential. While not necessary, I have greatly benefited from purchasing corner clamps so that I can get a true 90 degree angle on my beds.
Assembly
It’s obvious, but lumber has dimensions: you’re not joining two pieces of paper together. Where two pieces of wood meet at a corner (where they join), you need to carefully consider which piece of wood is “outside” that you screw the other piece of wood through. The shorter pieces should always be on the outside and you screw the short side into the longer piece of wood. For this reason, when calculating the actual length of wood needed for these long sides, you subtract three inches (1 ½ inches from each end) since the width of the short end of the wood makes up the difference. In an eight foot bed, instead of having long pieces of wood that are 96 inches long, you would make them 93 inches long. When they rest against the short sides of the bed, they have a total length of 96 inches.
Start on a level surface and build the first level of the bed. Connect one corner using clamps if you have them, making sure the short piece of wood is on the outside. Take time and be careful to make sure all cuts are made at 90 degrees and the wood is aligned exactly. Use wood glue between two pieces of wood. Using a drill, screw the shorter piece of wood into the longer one. Use two screws for this: one about four inches from the ground and the other about eight inches from the ground. Be sure to place the screws an inch from the edge of the wood and make sure you drive them perpendicular to the wood so they go straight in. Continue around the bed, twisting the corners until you have a complete rectangle. Do this a second time and you now have two rectangles. Usually you can just connect the second one on top of the first one since they should be copies of each other.
Then install the vertical supports. Place a 20-inch 2×4 in each corner vertically. Lay the longer side of the 2×4 along the longer side of the bed. Now screw the bed from the outside into the vertical support, securing four screws on each side of the corner. Go around and do this at all four corners and then every four feet along the length. The vertical support will not be as tall as the bed – it will need to be a little shorter. This will hide the supports once the soil is in the garden and will look cleaner.
If the bed requires a spacer in the middle, measure the distance between the width of the bed again and then cut two 2×12-inch pieces to that length. Secure them with wood glue and then screw the outside of the bed to the ends of the 2x12s.
Now move the bed into place. What I like about this process is that once you lower the bed, you can see exactly where you might have to level the ground a bit and can simply do it with a shovel while the bed is in place. Lift the bed, dig it out a little and put it back down. You don’t need to be precise about pre-leveling the space. Fill the beds with good soil and you’re ready to go. These beds are strong enough that you can tip a wheelbarrow in them without damaging the bed.
You can sand the corners to smooth them out a bit – a sander will do the job very quickly. I don’t stain or seal raised beds because I don’t want to add anything to the soil that could leach. However, in this case, you can use serum-based dyes.