After we got rid of the hot tub we were left with an 8 foot square gravel patch bordered in the ground with 2×6 pressure treated lumber. The idea has always been to use the area for one or more raised beds, and so we immediately set to work. Here’s what we ended up with, a nice solid redwood planter:
As you can see the design is very simple. There are four corner posts, which are 4×4 pressure treated lumber. You could use redwood for these as well, but in this design they sit in the ground, so PTL should last a bit longer. Then there are just four 8′ long 2×6 redwood boards for the sides, and 3’3″ long 2×6 redwood boards for the ends. Finally there are 2′ 2×4 redwood boards acting as center braces in the middle of the long sides. The whole thing is held together with 80 3″ galvanized lag screws.
The actual dimension will vary with your needs. You might not want it so high, but this gives more flexibility in planting, and it’s much easier to bend over to reach the plants. It does cost more though. Each redwood board (using redwood construction heartwood) cost $14.44 at Home Depot, is so each level is about $45 extra in lumber.
Here’s how it went down:
Since we already had buried PTL on three sides, I added another on the fourth side. This required some digging.
With the new buried support in place, I then dug out the four corners to a depth of six inches, ready for the corner posts.
Cut the 4×4 corner posts to fit across five 2x6s, which are 5.5 inches wide, so that’s 27.5 inches.
I marked all the posts installed in the same corner first, so I could ensure they ended up the same height in the other corners.
Four corners in place. Spend some time making sure they are upright and square, and that the tops are the same distance apart as the bottom.
We laid out the 2×6 redwood so we could pick the best five boards for the end and side that would face outwards. Boards with more imperfections were relegated to the back. Also try to pick the straightest boards for the more visible areas.
I started by assembling the back end. Start with a less visible area, so initial mistakes are hidden away.
I clamped everything together and made sure it was level. Note the defects in the wood, these will all be hidden inside the planter.
Got drills? Actually two drills and a driver. Since I was going to be alternating drilling two different sized holes, having two drills saved me a lot of time changing bits. The driver is for the lag screws, which you can’t really use a drill for.
This is a lag screw, also know as a lag bolt. It gives a stronger join than a wood screw or deck screw, but you could probably use them. I like lag screws because they are easy to drive (you can’t really strip the head), and they look cool. Note it’s also galvanized, which is required when using pressure treated lumber.
You need to drill holes for the screws. The first one goes in three inches, and is about the size of the inner diameter of the screw. Here I’m holding the drill bit I’ll use against the screw and you can see the threads on either side. You could probably use the next size down drill bit, it depends on how hard/soft the wood is. This worked out fine.
Here I’m drilling the narrow 3″ hole. You should mark where all the holes are going to go to ensure they end up in a straight line.
Then I drill the wider hole. This needs to be the same diameter as the lag screw, and just goes through the redwood boards (so 1.5″). To make sure I don’t go too deep I’ve added some tape to the bit.
Finally the lag screw should just slip in the first 1.5″, and then you drive it the rest of the way. You could use washers here for extra strength, but there’s no great need structurally, just be careful not to over-tighten them.
Drill, Drill, Drive. Repeat 80x.
The other side – once again keep checking everything is upright and square. In five years when you gaze yet again upon its geometric perfection you’ll be glad you took the extra minute.
And repeat for the other end.
I ended up having to trim 1/8th” off some boards, not too bad really. You could save yourself the trouble by building it upside down and out of the ground, but I was constrained here by the dimensions of the existing square, so needed to build around the fixed post positions.
You can’t clamp all the long boards before screwing them, so do them one at a time from the bottom. But while you do the bottom board, clamp the top board into place, so you know the posts are square. You will remove it for the third board, but then everything will be solid anyway.
Everything solid here. Repeat for the other side. Note here how the boards are uneven in the middle without the center brace.
When everything is together use the 2x4s to make a brace in the middle of the long sides. Remember to mark the holes in a line. Drive the screws into the boards that are flush first, and then drive the other screws while bending the boards into place so everything ends up flush.
We then lined the planter with 3.5 mil black plastic sheeting. This gives some extra protection to the wood, and will stop mud and water leaking out between the boards. The bottom is left open to the gravel, so there is no problem with drainage.
Then just fill with soil. It takes a lot, but you can calculate it fairly easy. Just 8 feet x 3 feet x the height you want the soil, in feet. The bed is two feet deep, so would take 8x3x2 = 48 cubic feet to fill completely. I went with 1.75 feet, so 8x3x1.75 = 42 cubic feet. That’s 21 of those bags. The bags weigh about 50 lb each, so that’s over a thousand pounds of soil. A good workout.
And done! now it just needs some plants.