Jakewins on data, food and technology.

Building a raised bed

Construction Material

Four planks and some dirt - how hard can it be? Turns out, building a raised bed involved quite a bit more than I thought!

This is part of my project to grow a meal, so I needed a bed that’s large enough to grow pasta for six people. Obviously I also needed a site that gets as much sun as possible. I’d made the mistake of putting a bed in partial sun before, hoping I could grow shade-tolerant vegetables, I’m not making that mistake this time.

The site

I got an ok from the landlord to put up a raised bed here, right where those stumps are.

Materials

Choosing material was a bit tricky - the frame will be in close contact with moist soil, so it'll rot if you're not careful. The ideal is cedar wood, which is naturally resistant to rot. However, cedar is rather expensive.

Naturally you might then reach for pressure-treated pine - but that is also a dead end, the chemicals they treat the wood with are not good to eat, you don't want to them leaching into your soil and vegetables.

So, what about regular pine? It rots like nobodies business. So I opted to try a middle-path: I built the frame with pine, but lined the inside with plastic. Hopefully that'll act as a barrier that helps keep the pine dry. I ended up paying $40 for the material to build 12x6x1-foot raised bed.

Plastic liner

Notice the plastic liner. Also - I'm putting strong steel wire across the middle portion of the bed. When winter comes, the soil will freeze and put significant pressure on the planks outwards, the wire will hold the bed together and keep its shape intact.

Squaring the bed

What really matters when building the bed is that it is level - otherwise water will not distribute evenly in it. But it also helps if it is square, since that makes it easier to keep neat rows. Making a 12x6 rectangle square is surprisingly tricky - and the trick is to measure diagonals. If both the diagonals across the bed are the same length, it is square.

You can use this to your advantage - get a piece of string as long as the diagonal you should have (figure out how long the diagonal is here), and use it together with a 12' and a 6' plank or string to make a triangle. As long as the string is tight, you'll have three corners of your bed perfectly marked out. Then just do the same thing for the last corner.

IMAG0850.jpg-resizedI used two strings and a plank for my triangle - one for the diagonal, and one for the short side of the bed.

Soil

The whole point of this was to create a space I could fill with real soil. Following recommendations online, it seems a 2-to-1 blend of top soil and compost is a reasonable thing to aim for. I'd hoped to get this from the local city compost, which is free to use for residents. However, after my second shovel of city compost I found a polyester sock in it, and I realized there were no guarantees for what other things might be lurking in the mulch.

So I went to Home Depot, and it turns out that buying good soil is surprisingly expensive - $800 for their mid-line soil to fill my frame. I went back online, and found recommendations for filling the bottom with leaves or mulch, and decided to try filling the bottom part with straw, which I then covered with newspaper to keep the good soil from seeping through:

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I regret doing this now for two reasons. One, I am the proud owner of a Ford Focus 2006 model, which the fine engineers at Ford Motor Company never intended once to be used for hauling straw:

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But more on point, because I've since learned that straw will make the soil excessively alkaline, hindering my plants from growing properly. It was also really hard to keep the straw an even 6-inches, since it was not uniformly compressed. I've got a soil testing kit that I'll use once it's all settled, and I'll have to try and correct any alkalinity.

The top six inches was then covered by a 2-to-1 mix of cheaper top soil and a manure/peat moss mix.

Hauling soil

All in all, the straw and soil cost me about $100. More than I'd anticipated, and I'm still rather worried I cheaped out and that I'll end up having a poor growing season because of it. We'll see!

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