Tools & Materials
- 1 4×4 8 foot pressure treated post
- 4 2×12 10 foot pressure treated boards (you could also get 2×10s or 2×8s, depending on the depth you want.)
- 2 2×12 8 foot pressure treated boards
- Decking/Pressure treated lumber screws, 4 inch length
- A tape measure
- A drill
- A shovel
Step 1: Cut the wood
Pressure treated lumber is perfectly safe to use in the garden, but that doesn’t mean you want to inhale it, so work outside and wear a dust mask.
Cut your 8 foot long 2×12s in half (do not cut your 10 foot long 2×12s).
Cut your 8 foot long 4×4 into 8 1 foot lengths.
Step 2: Do your layout
Layout the boards in rough fashion where you want them to lay. You do not need to dig up any sod, but if you like you can dig up the sod directly under where the boards will be, just to a depth of a couple inches.
Assemble the boards by first screwing a 4×4 piece to the ends of your 2×12 10 foot pieces. The 4×4 pieces are your corner blocks. Then stand up the boards, using an assistant if needed, and screw the 2×12 4 foot pieces (you made when cutting your 8 foot lengths in half) to the 4×4s thus forming the ends of your box.
Your box is now done, it’ll be heavy but you can with effort slide it around if you need to reposition it, if your ground isn’t flat and there are gaps use a shovel to dig down the high spots to better sit the box. You do not need to anchor it, it is heavy enough to sit still (especially after adding the dirt), but if you like you may drive short bits of rebar into the ground next to the inside corners.
Once you have it situated where you absolutely want it, move on to the next step.
Step 3: Cardboard
You now have a box filled with grass, this will not do. Lay down a thick layer of brown corrugated cardboard (the plain stuff), or newspaper. Either is perfectly safe to use in the garden and will fully decompose, but not before killing any grass below it. They’ll also provide compost and food for worms.
Step 4: Yard Debris
You have a perfect opportunity now to kill two birds with one stone. If there is any yard debris you want to get rid of, anything you’d normally compost, spent flowers, perennial or shrub clippings, kitchen scraps, grass clippings, you can dump it all into your boxes. The only caveat is if you add a lot of woody material also add a bag of blood meal to balance out the nitrogen. This material will slowly decompose once buried, feeding worms and providing the soil with nutrients way deep in the root zone.
Step 5: Fill with Dirt/Compost
I recommend directly using compost. Fill the boxes up with any compost you have, then at most garden centers you can buy bagged composted cow manure, do so and fill it up to the top. You could use regular top soil or garden soil, but compost is only slightly more expensive (pennies) and much more nutritious. It will not burn or harm or infect your plants, so go for it. You can also often get compost delivered by dump trucks from landscape companies. You will need around 100 cubic feet of dirt total, so you’re looking at a pallet of bags, or a single dump truck run.