In order to answer the question of how to build a Permaculture raised bed, first I might need to explain the word "Permaculture." Decades ago, the word was formed from "permanent" and "agriculture." It refers to using techniques of growing food based on the behavior of, and patterns in, nature. For example, nature doesn't use pesticides or herbicides, and nature plants a diversity of crops within a small area.
Today, the meaning of Permaculture has been broadened to mean "permanent culture." The underlying question this lifestyle seeks to answer is, "How can humans live in a way that respects the other animals, the environment, and each other?"
So when I talk about a "Permaculture" raised bed, I'm talking about a garden bed that is built purely from what nature gives, not out of ingredients purchased in plastic bags from a garden center.
You may have heard the term "lasagna gardening." Same thing. ;)
Preparing the garden site
The first order of business is to prepare the garden site. Measure out the length and width of the bed. Raised beds are three to four feet wide, depending on how tall you are (I'm barely five-foot-three, so I prefer three-foot wide beds).
Keep the length of any raised bed you build to ten feet or below. It might seem more space-efficient to have one twenty-foot long bed than two ten-foot long beds, but trust this voice of experience: it's really annoying when you have to walk ALLLL the way down to the end of a twenty-foot bed in order to get to the next bed parallel to it.
Once you've figured out the size of the area of the new raised bed, cut the grass and weeds down within the area as short as you can. If there is a particularly well-rooted grass growing there, such as Bermuda, that you don't want to eventually grow up into your bed, the best thing you can do is to find another location for your garden.
If you have such grass everywhere, dig out as much of it as you can, three feet beyond the borders of where your raised bed is going to be. But a heads-up: you'll be fighting with the grass several times a year for as long as you continue growing food on that site.
If the site of the future raised bed is on a slope, or on uneven terrain, you may want to level it so that the frame will fit flush against the ground.
The frame
Next, you're going to build the walls for the raised bed according to the size of the area. If you don't have the tools, strength, or skills to do so, you can buy raised bed kits.
If you're going to build the frame from scratch, your next step is to decide what kind of material you're going to use to build the raised bed frame.
If you live in a mild-summer climate, and you have access to a bunch of rocks that are all around six inches high, you can build the bed border out of rocks. This isn't a good idea for hot-summer climates, as the rocks will heat up. That heat will transfer into the soil, causing it to dry up more quickly and perhaps making the roots of your vegetable warmer than they want to be.
Most people are going to use wood. It's certainly easier on one's back to handle than large rocks! Use either two-by-six cedar boards or two-by-six pressure-treated lumber that the bed borders will last for many years.
The most permaculturish thing you can do when using wood is find some scrap lumber if you can.
Saw the boards to the correct lengths, then screw them together at the corners.
Once this frame is complete, place it over the mowed area.
Sheet mulch time
Now it's time to sheet mulch the entire area inside the frame. This simply means that you're going to cover the entire bottom with either cardboard, or four to six layers of newspaper. This will prevent weeds from growing while you build up the bed, yet still allow earthworms to get through.
There's something else you need to prevent, too: moles and voles. To that end, cut out hardware cloth (wire mesh) that will cover the entire width and entire length of the bottom of the bed. When I built our latest beds, we had chicken wire leftover that had been used to protect baby trees.
The holes in chicken wire are big enough for either a mole or vole to crawl through, so if you use it you'll need to use two layers. Arrange the top layer so that the holes of the bottom wire and top wire will be staggered. That way, you'll create holes that are too small for the critters to get through.
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The layers
Finally, we get down to business! This last step is the longest and will take the most work. However, within six months to a year you'll have a bed full of rich, loamy soil that you didn't pay a single cent for.
I happened to have put a case of bananas into the freezer just after I got the chicken wire laid down, so I spread out the peel at the bottom.
I continued with rotting leaves that had sunk onto the bottom of a small pond we use for supplemental garden and orchard watering. Some shale around the pond had also been washed into the pond and sunk to the bottom, which is what is giving the leaves that sickly gray color.
(Rotting leaves form the second layer of this permaculture raised bed.)
It really doesn't matter whether you start with a nitrogen-rich layer or a carbon-rich layer, but I'm going to arbitrarily pick nitrogen.
So...gather up enough nitrogen-rich organic material – grass clippings, weeds, and/or food scraps – to create a layer around three inches thick at the bottom of the bed. Next, scavenge up carbon-rich material: shredded paper, pine shavings, wood chips, or dried leaves. Pile them up evenly over the green material, six inches thick.
Keep on layering the organic material this way, alternating nitrogen-rich and carbon-rich materials. This layering method is why it's commonly known as "lasagna gardening". As when you prepare the pasta dish called "lasagna," you alternate layers of the different ingredients.
Do your best to layer on two parts carbon-rich materials to one part nitrogen-rich, as the materials will compost more quickly if they are used in these proportions. However, if you have mostly grass clippings or mostly dried leaves available, you can pile them up and still eventually end up with the same result. But the material will take longer to compost, and if it's nitrogen-rich material, it will stink in the process!
We used to live in north Texas, where the native soil is thick clay. Even after tilling in the amendments recommended by the local organic gardening guru, my vegetable garden soil was still hard to work with.
So, one fall, I collected all the dried leaves I could from neighbors, piled them a foot high in the garden bed, and covered them with cardboard and bricks so they wouldn't blow away. By the next spring, I had two to three inches of much richer, softer soil. So you don't have to mix the carbon and nitrogen materials in order to end up with beautiful compost at the end.
(Weeds and grass clippings top the layer of leaves.)
Keep on layering the materials as high as you dare. Accomplish this by heaping up the materials several inches above the six-inch edge of the Permaculture raised bed frame in the center of the bed, then have the materials gradually sloping down toward the edges of the bed.
If you have finished compost on hand, plop that on the very top. If you don't, cover the bed either with biodegradable black plastic or with cardboard. Weight your cover down with bricks or rocks so they won't blow away.
Finally, let the earthworms and microbes do their thing. Give them at least four months to break down the organic matter. The longer you wait, the more of the matter will have broken down; however, if only a third of it has composted and the rest of the matter is in various stages of breaking down, you'll still be able to grow vegetables in it.
Enjoy the bounty!
That's how to build a Permaculture raised bed, or lasagna gardening bed. No shelling out big bucks for potting mix, or the ingredients for potting mix. No purchasing materials whose sustainability is debatable, such as peat moss or coconut fiber.
And what you'll end up with is a soil much richer in both nutrients and beneficial microbes than anything you can buy from a store.
