So my girlfriend has been getting into gardening lately, and I wanted to do something nice for her (plus I get to build stuff). I came across the square foot gardening method of using raised boxes, and that's where it started. "Honey, I will build you a garden box," couldn't possibly be that simple for me, so in my usual WAY over the top style I had to amp it up about fourteen notches.
Here you see some [very] rough sketches of the box concept, along with my materials list, both of which ended up changing along the way. Dimensions are 2'W x 6'L x 34"H, so you can reach the entire span of the box from one side, as well as stand comfortably without leaning while you work. The box will be self watering, in the sense that there will be an internal water reservoir that will only need periodic filling, and the soil will only pull up what water it needs through the wicking process. The base of the box stands at 14" off the ground, and the internal box depth is 16 3/4" after subtracting the thickness of the frame and bed. This gives me room for my layers as follows: The box will first be sanded and treated with linseed oil to protect it, then I will install landscape fabric or burlap to protect the plastic from sharp edges, a layer of 6mil plastic to make the inside water proof, another layer of fabric, the PVC pipe system, a 4" layer of gravel as my wicking medium, another layer of fabric, 10-12" layer of soil mix, and then mulch on top. I will also be adding some trim and decorative pieces to the top, and incorporating a level indicator into the watering tube. I got lots of good information from this website http://www.resilience.org/stories/2011-05-31/bottom-diy-guide-wicking-beds
Some quick math told me I would need 8 cubic feet of gravel, which will displace ~60% of the water layer, giving me somewhere in the neighborhood of a 13 gallon reservoir. Using conservative estimates of weight per cubic foot of soil, water, and gravel, the total weight of my full box would be close to 1500 pounds. This means every square foot of box space must support 125 pounds since I was determined to make it elevated. Not only that, but it would need to withstand the outward pressure of a half ton of wet soil. GAME ON. If there is anything I'm good at, its over-engineering the hell out of stuff. I set my bar at being able to jump around inside the box with the intent of breaking it and it not budging an inch.
This is the completed bed support frame, the cornerstone of the whole box and my first real attempt at using any sort of joinery (if you want to count lap joints). It is constructed of 2"x3" studs, cut to 6' and 2' lengths, and lap joints every foot on center. The two outer most laps are on the opposite side, allowing the outside pieces to be flipped over. In this manner, even dry fit I can pick up the frame from any piece as it is completely interlocked. I wanted to finish the project with NO fasteners showing, so I predrilled holes along the inside of the bed frame to attach to the sides. Then I glued the laps together and placed a sheet of 3/4" plywood sheathing on top, drilling screws down and through the center of every lap joint.
The sides are just butt jointed together with 3" wood screws, and at this point are not attached to each other at all. Each level is just its own floating rectangle until the legs are attached.
Underside of the box, here you see the frame is hidden by being flush with the bottom side rail.
Here I have assembled all four layers of side rails and installed the legs. The legs are just 2'x4' butted and screwed to 2'x6' boards, but I used an oak dowel to make plugs and hide all the screw heads. I predrilled holes from the inside to attach all the legs, and fastened with 2.5" "high performance exterior screws". They had a 5lb box on clearance for $9, and they are far superior to the wood screws I was using as proven by a quick test. I screwed half of each kind of screw into a scrap 2"x3" and hit them sideways with a hammer. The SPAX construction screw snapped on the second light tap, whereas the exterior screw I was able to bend all the way over and then all the way back up before it snapped.
I put the box on the ground and romped around in it with all 200 lbs of myself and its solid as a rock...BUT!--I am not satisfied. As it stands, the sides can still be considered not attached to each other, all the downward pressure on the bottom frame is supported entirely by the screws from the bottom side rails into the legs. In order to remedy this I need to install some bracing vertically on the sides that is not in contact with the ground, then the load can be spread onto the rest of the fasteners on all the side rails into the legs, thus adding tremendously to the strength. I've got some leftover 2'x4' which I plan on cutting 20" lengths and putting at 2' and 4' on center on each side. After that I need to figure out what kind of molding and corner squares I want to use.
Hoping to get to the braces in the next couple days, then have it sanded and finished with linseed oil by this weekend. I haven't even started on the PVC system yet, I gotta drill a sh$$load of holes -_-
This may be more of a gardening project than a woodworking project, but I am building it with wood so I think it counts! I do wish I knew more about construction, I'm fairly certain I have used 100% more materials than necessary, and that you could most likely set a tank on this. But hey, all part of the fun I guess.
More to come...

Here you see some [very] rough sketches of the box concept, along with my materials list, both of which ended up changing along the way. Dimensions are 2'W x 6'L x 34"H, so you can reach the entire span of the box from one side, as well as stand comfortably without leaning while you work. The box will be self watering, in the sense that there will be an internal water reservoir that will only need periodic filling, and the soil will only pull up what water it needs through the wicking process. The base of the box stands at 14" off the ground, and the internal box depth is 16 3/4" after subtracting the thickness of the frame and bed. This gives me room for my layers as follows: The box will first be sanded and treated with linseed oil to protect it, then I will install landscape fabric or burlap to protect the plastic from sharp edges, a layer of 6mil plastic to make the inside water proof, another layer of fabric, the PVC pipe system, a 4" layer of gravel as my wicking medium, another layer of fabric, 10-12" layer of soil mix, and then mulch on top. I will also be adding some trim and decorative pieces to the top, and incorporating a level indicator into the watering tube. I got lots of good information from this website http://www.resilience.org/stories/2011-05-31/bottom-diy-guide-wicking-beds
Some quick math told me I would need 8 cubic feet of gravel, which will displace ~60% of the water layer, giving me somewhere in the neighborhood of a 13 gallon reservoir. Using conservative estimates of weight per cubic foot of soil, water, and gravel, the total weight of my full box would be close to 1500 pounds. This means every square foot of box space must support 125 pounds since I was determined to make it elevated. Not only that, but it would need to withstand the outward pressure of a half ton of wet soil. GAME ON. If there is anything I'm good at, its over-engineering the hell out of stuff. I set my bar at being able to jump around inside the box with the intent of breaking it and it not budging an inch.

This is the completed bed support frame, the cornerstone of the whole box and my first real attempt at using any sort of joinery (if you want to count lap joints). It is constructed of 2"x3" studs, cut to 6' and 2' lengths, and lap joints every foot on center. The two outer most laps are on the opposite side, allowing the outside pieces to be flipped over. In this manner, even dry fit I can pick up the frame from any piece as it is completely interlocked. I wanted to finish the project with NO fasteners showing, so I predrilled holes along the inside of the bed frame to attach to the sides. Then I glued the laps together and placed a sheet of 3/4" plywood sheathing on top, drilling screws down and through the center of every lap joint.

The sides are just butt jointed together with 3" wood screws, and at this point are not attached to each other at all. Each level is just its own floating rectangle until the legs are attached.

Underside of the box, here you see the frame is hidden by being flush with the bottom side rail.

Here I have assembled all four layers of side rails and installed the legs. The legs are just 2'x4' butted and screwed to 2'x6' boards, but I used an oak dowel to make plugs and hide all the screw heads. I predrilled holes from the inside to attach all the legs, and fastened with 2.5" "high performance exterior screws". They had a 5lb box on clearance for $9, and they are far superior to the wood screws I was using as proven by a quick test. I screwed half of each kind of screw into a scrap 2"x3" and hit them sideways with a hammer. The SPAX construction screw snapped on the second light tap, whereas the exterior screw I was able to bend all the way over and then all the way back up before it snapped.
I put the box on the ground and romped around in it with all 200 lbs of myself and its solid as a rock...BUT!--I am not satisfied. As it stands, the sides can still be considered not attached to each other, all the downward pressure on the bottom frame is supported entirely by the screws from the bottom side rails into the legs. In order to remedy this I need to install some bracing vertically on the sides that is not in contact with the ground, then the load can be spread onto the rest of the fasteners on all the side rails into the legs, thus adding tremendously to the strength. I've got some leftover 2'x4' which I plan on cutting 20" lengths and putting at 2' and 4' on center on each side. After that I need to figure out what kind of molding and corner squares I want to use.
Hoping to get to the braces in the next couple days, then have it sanded and finished with linseed oil by this weekend. I haven't even started on the PVC system yet, I gotta drill a sh$$load of holes -_-
This may be more of a gardening project than a woodworking project, but I am building it with wood so I think it counts! I do wish I knew more about construction, I'm fairly certain I have used 100% more materials than necessary, and that you could most likely set a tank on this. But hey, all part of the fun I guess.
More to come...