How To: Build a Garden Planter Box
Like many people locked down by the pandemic this Spring, I decided it was time to step up my gardening game. Although I had plenty of time on my hands, my budget was limited, so I decided to build a planter box in my backyard.
Raised bed gardening has some decent benefits:
- They get fewer weeds
- You can control the soil rather than mix with your local soil (clay, in our case)
- The soil stays warmer in the early spring and late fall, extending your growing season
- And they’re just more comfortable to work in
Building a decent sized planter box doesn’t have to be complicated or expensive. I found these planter building blocks at Home Depot for under $4 a piece:
The slots on them are designed for the edge of a 2x6 wooden board. With a few blocks and some lumber, you can build any shape box you’d like and even incorporate multiple tiers. The hole in the center of the block is used to drive steel rebar through to anchor them into the ground.
For my project, I had space for a six-foot by three-foot box. Tiers didn’t make a lot of sense because of the way the sun hits this area, so I kept it simple.
This is the list of materials I used for my planter box. Yours may differ depending on the slope of your land and the size of the box you build.
-  Planter Wall Blocks ($3.50 each)
-  2x6x8 pre-treated “ground contact” rated boards ($8.50 each)
-  1x6x8 boards or decking boards ($7.50 each)
-  ½ inch by 4 ft #4 rebar ($4.00 each)
STEP 1: The first step is to dig out your area and position your first blocks.
Always call your local utility company or city organization to have underground lines marked. It’ll ruin your day if you cut out your cable, power, or water, and it could be dangerous and expensive to fix!
To keep the structure sturdy, you want the blocks at least partially below ground, but level with each other. You can use your 2x6’s laid across the top of the blocks to level them. My project was on a noticeable slope, so leveling them meant stacking some blocks three high to be level with a single block on the other side.
Here I’ve finished digging out the base. The blocks are level, and I have channels dug, a bit too wide, for the 2x6’s that will connect the lowest blocks. Like the blocks, you want the 2x6’s to be a little bit under the ground level. Be careful not to leave a visible gap between the bottom of your 2x6 and the ground. This will prevent dirt and water from escaping out the side of your box.
I also installed irrigation tubing under the box. It’s very dry where I am and I don’t feel like watering by hand every day. The tubing is connected to an automatic sprinkler system so I can set the watering schedule.
STEP 2: Set up the blocks in their final position.
Here, I have all the blocks stacked up to the same height. I needed a good number of them because of the slope of my yard. That’s never more visible than when you try to make something level!
In this step, check that the tops of your blocks are all level still. You may need to do a little more digging or even add some dirt back in to get them both level with each other and stacked so they stand up straight.
Then, check that your boards have a place to sit that will be on or below the ground. This is a good time to dig out your channels for your 2x6’s if you haven’t finished that yet.
STEP 3: Add the boards and rebar.
With everything level, it’s a simple matter to cut 2x6’s to fit and drop them in place. Wood and dirt are not perfect materials to work with, so be sure to measure for each and every board you’re going to place.
Once the boards are in place, drive the rebar into the ground to lock it all down. For my design, the rebar should stick out of the blocks at least three inches (a little more at this step so you have room to work). You should get rebar that is long enough to have at least one foot of rebar in the ground for stability.
I also added some concrete cement between the blocks for a little extra stability, but it probably wasn’t necessary.
STEP 4: Add boards to the top to serve as a seat.
I used decking boards for their ability to withstand the weather and drilled holes where the rebar would poke through.
Pro-tip: You can put the board in place above the rebar sticks up and give it a whack with a rubber mallet a few times. That should leave an imprint of the rebar exactly where you need to drill the hole in the board. It’s still more accurate to measure, but this is a fast way to get close enough.
I used two layers of decking cross-hatched for stability. This locks everything together tightly with the rebar holding each side of the “seat” in place. Add a few deck screws into the 2x6’s to hold everything together, and you have a very solid surface. My kid likes to use this as a balance beam… so do I if I’m honest.
STEP 5: Fill it up
To set up the box for use, I cut and clamped my irrigation tube and added some drip lines. Then I stapled in some ground cloth, shoveled in some dirt (about 20 cubic feet), and planted flowers! Several weeks later, we have lots of blooms and a nice place to sit when we’re working in the garden. All for a total cost of $250 and about 6 hours of work.
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