It’s been my goal to tidy up the garden and eventually move to a raided bed system. I’d independently slated a deck for demolition, and put two and two together. The main problems which I’ve tackled are, forst, the pressure treated wood from the deck is not to be used without a little research and planning. It contains ‘CCA’, which is Copper Chromate Arsenic. The second aspect of this raised bed design was to come up with something that was flexible enough to let my garden continue to evolve. By that, I mean the garden is forever changing, and I wanted a raised bed system that gives me options.
First, on that CCA issue, and whether I should even go ahead with the pressure treated lumber. This link was probably the most cautionary. http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/CCA%20wood.pdf She has some other good ‘horticultural myths’ sorts of information, here:http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/
Some other sites mentioned that diffusion of the CCA goes mostly straight down, not lateral across the bed, and that most of the free CCA will come out in the first year. Without getting into the details you can read at the site, I am going ahead with using the pressure treated lumber with the following precautions:
- Wood stain on the inside, and/or heavy plastic.
- No cabbage family, as they concentrate arsenic,
- no root crops within 6″ or so from the edge,
- No tilling after initial planting, till only in fall.
My research was not comprehensive, and I welcome comments and new information, but I did not find an overwhelming amount of ‘negative’ data on the topic, so I’m going ahead thinking it’s not completely safe, but manageable. Certainly, I’m glad the timber I have is from a 20 year old porch that should be somewhat leached out.
Well, on to the second aspect of this, the design of the prototype. Here’s a picture of the deck in dissassembly to show what I’m working with:
Above I’m just tearing up the old deck surface, and removing the nails. Still have to fabricate the building blocks.
Below, I’ve built two pieces, the first two, in order to se how it works.
The base unit is 12′ 1″ long, and 4′ wide. The top unit, sitting at the back there with the little pink flag, is 4′ square. In the corners, I nailed (ring nails using a framing nailer) a block 5 1/2″ long, which is the same height as the 2×6’s on the frame. The trick is the corner blocks are secured 1 1/2″ lower than the frame, so they form little guides that sit into the frame below.
With this system, I can stack the 4′ squares on the base frame and increase the height of the frame as compost is added, or as I switch from one crop to the next. For instance, I have onions in the lower 8′ x 4′ long section of the 12′ bed. The upper section, contains lettuce, which is a bit of a waste, as I have a foot of soil below the lettuce. But, that part of the frame would work very nicely for carrots or some other root crop.
With the base frame at 12′ 1″, I can stack 3 sets of the 4′ squares, one set might be two high, for a total of 18″. If I put another 4′ section on, it goes to 24″ of height. I reckon in the fall, if I want to pull a top frame off, and refresh a bed, I can do so and not have to dig down in alongside the frame.
I ‘secured’ the 12′ base frame with a couple bits of re-bar along the side, and at the lower end, I used some PT lumber to keep the soil in the frame. Those I call ‘dirt skirts, and they also help hold the base frame level, (at least till the frost?).
My plan is to build more of the 4′ frames and have them at the ready as new crops go in, and to install more of the 12’ 1″ ‘base frames’. I might put those base frames at various angles to the first one to make the garden interesting, and I might make some really long ones, perhaps 16′ 2″ or thereabouts. The extra 1″ and 2″ is so I can have a little wiggle room to stack either 3 or 4 of the 4′ frames along the length of a longer ‘base frame’, and not have them fail to seat properly due to small inaccuracies in my framing, or the squaring of the base frames.
I hope the pictures post OK…..I’ll take a detailed construction picture next weekend. Happy gardening all.