How To: Build a Rot-Proof Garden Bed

Living in Florida any time I put a piece of wood outdoors the clock starts counting down until it starts looking ugly and rotting which makes my garden and yard look unkept. I finally got fed up with it and decided to build something better. This post was sponsored (and inspired) by my friends at Cabot who asked me what outdoor wood project I could build for them like the DIY Adirondack Chair I made last year using their awesome finishes.

I always loved the idea of a raised garden bed to make gardening easier and more attractive, but using pressure treated lumber for edibles is a big no-no due to the chemicals in the wood, so I was left wondering what would hold up outdoors in Florida. Working with Cabot made me see things a little outside the box (pardon the pun), so I retired to my secret lair and developed plans for an attractive AND rot-proof garden bed.

Is a Rot-Proof Garden Bed Possible?

You can always use pressure treated lumber for a garden bed which can last a good long while but when you use wood treated with chemicals like ACQ (alkaline copper quaternary), Copper Azole, Copper Naphthenate, Copper-HDO, Borate, or Polymeric Betaine you can’t have a garden bed that can grow anything even remotely edible.

These chemicals leech into the soil which makes edible gardening verbotten. Plus, pressure treated lumber always has an ugly green color to it which doesn’t make it a good fit for an attractive stained wood feature in your garden which is something we all want, right? Beauty!

That leaves many folks choosing more rot resistant woods like western red cedar or redwood which are extremely attractive, but their rot-resistance is not up to my standards since they will only last a few years when in contact with the ground or dirt here in rainy and sunny Florida.

It took a little digging to find the perfect wood for my rot-proof garden bed and it is called Accoya. Accoya is sustainably grown radiata pine that has undergone a process call acetylation. This process treats the wood with an industrial vinegar resulting in a harder wood that is both non-toxic and extremely rot-resistant.

I have used Accoya in my window restoration business Austin Historical for years to build doors and windows, but I never really thought about it for an outdoor garden project.

Accoya even comes with a 50-year above ground and 25-year below ground warranty against rot. Not only that but it is resistant to insects like termites and other wood destroying organisms (WDO). That means I can build a garden bed that will last me into my retirement years and not have to rebuild it again! That kind of lifespan is what I want for the Florida weather.

Not only that but the wood has a nice clean grain pattern since it is pine and it takes stains and finishes very well which is exactly what I want for my garden.

Building the Garden Bed

Accoya comes in the “rough” which meant I had to joint and plane it to get it cleaned up and ready for construction. If you don’t have the ability to mill the wood yourself you can always take it to local woodworker to get it dressed.

Once the lumber was dressed I measured out my garden and decided to go big time! I laid out a 3’ x 8’ garden bed to grow fun edibles like watermelon, strawberries, cucumbers, and mint. I wanted the bed to be about 22” high to make the back breaking work less, well, back breaking.

Next I cut all the boards to length and laid everything out. I used simple butt joints for the corners with supports every couple feet to keep the boards aligned. Since this garden bed was going to hold hundreds of pounds of dirt I need to make the boards out of 1 1/2” thick Accoya as opposed to the thinner 3/4” material of most raised garden beds.

Tools & Supplies

• Cabot Australian Timber Oil
• Accoya Wood
• Stainless Steel #6 2 inch screws
• Stainless Steel #10 3 1/2″ screws
• Countersink Drill Bit
• Purdy 3″ Sash Brush

Putting everything together with stainless steel screws since this is an exterior project will also prevent staining on the wood over the years. Once the bed was assembled I went through and sanded everything smooth in preparation for staining. A quick wipe off of the wood and we were ready for finishing.

Exterior Wood Stain

Cabot makes the perfect products for exterior wood projects whether they are in your garden or on your porch. Just like Adirondack chair last year I went with Cabot’s Australian Timber Oil for a warm natural finish on my rot-proof garden bed.

Shake the can well before application and then using a natural bristle brush I applied the finish working in the direction of the grain. To keep the finish looking consistent and for the best performance Cabot recommends applying only one coat. Be careful not to overlap your strokes or you may get some color differences. Australian Timber Oil is available in multiple colors, but even the natural color leaves a nice warmth to the wood and provides a lot of protection as well.

Australian Timber Oil is not a food safe finish so for this garden bed I applied it only to the exterior portions of the wood. The inside would be filled with dirt and not visible other than the top 1″, so by finishing the exterior I was able to really warm up the wood and not have any issues with growing fruits and vegetables safely.

Filling the Garden Bed

I let the finish dry overnight before filling the bed with a mixture of soil, compost, and yard waste to keep the soil from compacting. Since this was going to be an outdoor bed placed directly on top of dirt I didn’t have any need to build a bottom to the garden bed and with the 22” height there wasn’t any weed blocking needed either.

Once my rot proof garden bed was filled I was ready to start planting. It’s a big garden bed with nearly 40 cubic feet of interior space so we had plenty of room to grow fruits and veggies that would thrive in our warm climate and start producing our own food.

I was really pleased with how it turned out and I’ll be sure to post an update on how our harvest is as the plants progress. I’m not sure how green my thumbs will be, but at least I feel confident that this garden bed will last years thanks to Accoya and look great thanks to Cabot.