Bowing is usually the first thing to go wrong after building raised garden beds from wood. It occurs when the interior side of the wood is wet while the exterior is dry, causing expansion and contraction that warps the bed’s walls. However, if you add some extra structural elements to your garden bed and build it right, you won’t ever have to deal with bowing beds again.
Here’s how to keep your raised garden bed from bowing:
- Use warp-resistant building materials for raised beds.
- Finish and seal your garden bed’s wood.
- Add a cross structure inside the base of the bed.
- Stake raised beds generously.
- Line the inside of the bed with plastic.
- Screw metal brackets and reinforcements in the gaps.
- Add extra support with exterior cross pieces.
- Create a structural border around the bed.
If you want your garden beds to stand the test of time and stay intact, stick with me. I’ll tell you how you can use these reinforcement methods to prevent your garden bed from bowing and help you keep your raised garden beds straight as a (non-bowing) board.
1. Use Warp-Resistant Building Materials for Raised Beds
Most people recommend using hardwood for constructing raised garden beds since softwood decays more readily.
However, softwood also warps more quickly since it has soft, porous fibers that absorb water like a sponge. This moisture retention makes the fibers even softer, allowing forces like gravity and the pressure from the soil inside your bed to move and warp the boards.
Likewise, the expansions and contractions that occur as the wood dries will result in more extreme warping with absorbent softwoods like pine.
On the other hand, hardwood is much denser and features tighter grains, making it warp-resistant. So, choosing hardwood or other more rigid building materials like composite deck boards can help you ensure that your garden bed doesn’t warp.
However, the one drawback to using these materials is that they can be more costly than softwoods.
Still, since your bed will last longer, you will likely have to repair or replace it less frequently than one made with softwoods. So, you may ultimately save time and money by opting for a rigid building material that resists warping.
2. Finish and Seal Your Garden Bed’s Wood
Since dampness and pressure cause garden beds to warp, waterproofing can go a long way in keeping the walls straight. You can use natural oils such as linseed, tung, mineral oils, or a plant-based sealant for a garden-safe water-resistant finish.
Likewise, sanding your wood can eliminate tiny splinters and recesses where water can accumulate.
So, take your time to finish off the garden bed. It’ll look more attractive and last longer, so it’s well worth it.
3. Add a Cross Structure Inside the Base of the Bed
Although most people leave the interior of their raised garden beds open and unbuilt to allow for drainage, adding a simple cross-shaped structure that goes diagonally underneath the bed can bear some of the bed’s load, keeping the corners strong and the panels from warping.
This structure should consist of two long pieces of wood, metal, or other material screwed into each opposite corner of the frame to make an X-shape.
4. Stake Raised Beds Generously
Staking garden beds does many things to help you keep your raised bed in tip-top shape. Staking keeps the structure from sliding and collapsing, and it can also ensure that your bed’s walls don’t bow and warp.
It is usually only necessary to stake the corners of your bed when you want to prevent it from sliding around, but you can add extra stakes along the bed’s walls on either the inside or outside of the structure to fight warping. Screw the garden bed’s frame into the stakes for a lasting and secure hold.
For in-depth steps for staking your garden bed and tips on choosing the best materials, check out my article on the topic: Do Raised Garden beds Need To Be Staked
5. Line the Inside of the Bed With Plastic
Lining the interior of the garden bed with a tarp or plastic sheeting can reduce the moisture that accumulates inside wooden garden bed walls, ensuring that the wood doesn’t become so saturated that it warps and bows as it dries unevenly.
Lining the bed with plastic has some other benefits, and it’s a necessary precaution when you choose to use pressure-treated wood to make your raised bed.
However, be sure not to cover the garden bed’s floor with plastic. If you cover the floor, water won’t be able to drain from the bed, potentially introducing root rot and fungal infections in your plants.
6. Screw Metal Brackets and Reinforcements in the Gaps
Adding metal reinforcements anywhere there’s a gap in your garden bed, from the corners to the small slits where two planks sit atop each other, can ensure that the boards don’t bow.
Here are some ideas for incorporating metal brackets and reinforcements that I’ve used with success in the past:
- Place L-shaped steel brackets in the bed’s corners. Corner brackets are ideal tools to help you secure your garden bed’s walls to stakes and sure up the corner joints. These brackets, in particular, are very affordable and come in a 16-pack, making it easy to offer your garden bed all the reinforcement it needs to fight bowing and warping.
- Use mending plates to reinforce gaps between planks. Galvanized steel mending plates are perfect for strengthening the weak spots where the planks of your garden bed walls meet. These are galvanized steel, which lasts in damp outdoor conditions and under moist soil, offering your raised bed long-term protection from bowing, warping, and collapsing.
- Use a garden bed brace. Suppose you want to add a bit of aesthetic appeal to your garden bed while keeping the corners secure. In that case, I recommend using a reinforcement like this Garden Bloom Dragonfly Instabrace (available on Amazon.com). This product isn’t as cheap as standard steel L-brackets, but it is long-lasting and makes your garden beds look fantastic while holding the corners right where they should be.
7. Add Extra Support With Exterior Cross Pieces
Adding vertical and horizontal slats of wood along the exterior surface of your garden bed can seal up gaps and offer some extra reinforcement to ensure that the wood doesn’t bow.
I recommend placing vertical slats along the bed’s walls at 1-foot (30 cm) intervals. Then, if you want to do the job right, put some horizontal slats anywhere there are gaps or slits between your walls’ layers.
When installing these slats, be sure to use screws and wood glue. If you use nails, the bed’s walls may warp anyway, causing the wood to slide off the nail. However, when you use both screws and wood glue, the slat will grab the wall securely and never slide off.
Add as many of these slats as you want. There’s no such thing as too much security for your garden beds.
8. Create a Structural Border Around the Bed
Last but not least, adding structural elements to the bed’s base can ensure that the bottom of your garden bed has enough extra support to resist warping.
Since raised garden beds don’t have a firm grasp on the ground, they can benefit from some solid fortification near the bottom. You can use almost anything to help keep the bed where it should be. Here are some ideas of materials that you can place along the bottom of the bed to keep it stable:
- Large stones
- Bricks
- Pavers
- A path
- Potted Plants
- Cinder blocks
- Grass and other deep-rooting plants
These objects can all add a bit of resistance if your bed’s planks start to warp outwards, keeping the bowing minimal.
Final Thoughts
There are tons of ways to keep your garden bed from bowing, and incorporating one or two of these reinforcements (or all of them!) can only add some extra protection and a few more years of life to your raised bed.
