Feed the soil. Free your back. Save the world. Here's how you do it all the easy way.
Superyard Farms owner-operator Oakley Anderson-Moore with a truckload of leaves for composting.
There’s nothing as good for your garden, and arguably the planet, as making your own compost. Fruit, vegetables, flowers, and trees grow bigger and stronger than with any store-bought fertilizers. And instead of adding to the global demand for synthetic fertilizers derived from petroleum products, you can make yours for free. Not to mention that in the process of composting, you keep precious raw materials out of landfills.
There’s only one catch.
And that catch is your back. It’s a lot of work to turn a compost pile by hand, especially when you have a lot of it.
That’s where ASP comes in – aerated static pile. The “static” part of this abbreviation is the part that means “you don’t have to turn it.”
We first heard of ASP compost at Superyard Farms as a footnote in The Lean Farm by Ben Hartman. Up to that point, we reveled in both our resourcefulness and physical abilities of hauling, shoveling, wheelbarrowing, turning, and creating all our own compost on-farm from local sources. But as our network of neighborhood farms started to grow, we realized there was no way we could keep up with this level of back-breaking manual labor.
Following up on the crumb from Ben Hartman, we checked out Community-Scale Composting Systems: A Comprehensive Practical Guide for Closing the Food System Loop and Solving Our Waste Crisis by James McSweeney from the Flagstaff Public Library. In it was an entire chapter devoted to ASP.
In Northern Arizona, there is an amazing non-profit organization called Flagstaff Foodlink that is devoted to supporting local growers and a sustainable community food system. We are thrilled to say that in 2021, we received a Growers Grant from Flagstaff Foodlink to implement an aerated static pile on our farm.
And we are excited to report that it has been pretty awesome. We successfully fed over 22 families with our neighborhood farm share for the Summer and Fall seasons, delivering somewhere around 2,000 pounds of fresh fruits and vegetables. All of our produce was grown using locally-sourced, on-farm made compost that went through our aerated static pile. We had continuously abundant harvests with minimal pest and disease pressure. Our plants grew tall and beautiful. And we did not turn a single pile.
Want to know how it works, and how to build or retrofit one yourself? Here’s a primer.
First, how does compost work?
When you pile the right ratio of organic matter into the right height by width, a compost pile heats up. That’s because when we create a pile, we’re creating the right conditions for millions of our microorganism friends. The microorganisms revolve around decomposing raw materials in your pile.
Thank you, microorganism relatives! Without you, there’d be no crumbly, nutrient rich compost. There'd be no soil, no plants, no animals, and certainly no us.
When you start a compost pile, the first group of microorganisms come during the mesophilic stage. They are the ones who first heat up the pile. Once the pile is heated, different microogranisms, who love heat even more, take over. That's when we enter the hottest thermophilic stage. So creating a compost pile is creating the right conditions for these two groups of microorganism friends to do their work.
If you’ve composted before, you could consider yourself a kind of microorganism zookeeper. That’s right, feel free to go gleefully shout, “We bought a zoo!” at your neighbors. They probably already think you’re crazy! (Or admire you. Or support you. Or just want to know how your vegetables get so big.)
Why do we turn compost piles?
The main reason to turn compost piles is to get oxygen into the pile. There are four main ingredients that our microorganism friends need to successfully compost your pile: carbon (often in the form of dried brown leaves, shredded cardboard, shredded pine needles), nitrogen (often in the form of livestock manure or food scraps), water, and air.
Generally, when you add the first three and get the ratios right, you don’t need to add any later. But air – that runs out in the middle of the pile no matter what. As a pile starts to break down, it naturally compacts, and microogranisms eventually ‘breath in’ all the air inside the pile.
When oyxgen runs out, the microogranisms stop. And when these microorganisms stop, the heat goes out, and the compost process stops too.
In some extreme conditions, anaerobic bacteria who don’t need oxygen can take over the pile and leave you with more of a foul smelling slime than that nice black gold compost.
So when we “turn” a compost pile, the main reason is to get oyxgen back into the pile.
How aerated static piles (ASP) are different, and why they are better than hand-turned alternatives
An aerated static pile pumps oxygen evenly into a compost pile by means of a blower motor and a perforated manifold. A typical ASP setting on a small farm scale will blow air through a perforated PVC pipe into a compost pile for 30 seconds every 30 minutes. This ensures that throughout the thermophilic phase of compost, which lasts only 30 days this way, oxygen is supplied evenly to the pile. There is no turning needed.
One of the best things about an ASP is that because the oxygen stays even, so does the heat. As we mentioned, when you turn by hand, you run out of oxygen and then run out of heat. But similarly, in the process of turning the pile, you are introducing an extremely high amount of oxygen into the pile at one time. This results in temperatures skyrocketing right after the turn. When a pile gets too hot, too quick, it burns up nitrogen and nutrients that we’d rather hold on to.
Alex Reinhard converts the Superyard Farms three-bin compost to aerated static pile.
How to make an ASP Compost System
1. Make or retrofit a compost bin to fit the ASP manifold.
In our dry climate of the arid West, we’ve found it useful to have a compost bin that is sealed to prevent excessive drying. (Not to mention, looks nice in our semi-residential area and keeps critters out!) We built a 12’x 4’ x 4’ three bin compost system that is fully enclosed with wood. However, you could use any existing compost bins as well as open air windrows, which are especially effective for farmers with space.
The only specific need when building or converting to an ASP pile is to drill holes in the bin for your ASP manifold, aka perforated PVC, ABS, or equivalent pipe. We drilled these about a foot off the ground, and allowed for two pipes per chamber to ensure even air.
2. Use PVC or ABS pipes + elbows, plumbing flanges, and a drill to make the ASP manifold. We drilled holes with a ½” drill bit at twelve o’ clock every two inches or so.
3. Connect the ASP manifold to a blower motor and a timer.
At the small-farm and backyard grower scale, blower motors for bouncy houses just happen to work perfectly. We set our to go off for 30 seconds every 30 minutes during the first 30 days.
4. Cover the ASP pipes in the compost bin with a healthy layer of wood chips.
This is called the “plenum layer” and ensures that the air is distributed to the pile evenly and compost never blocks the holes.
5. Wet down your organic matter.
With ASP, you want the pile to have enough moisture so that it doesn’t dry out with the added air. How much to douse depends heavily on what kinds of organic matter you are using. Food scraps tend to be very wet, for example. But spent livestock bedding is usually very dry by the time you get it. So in general, we recommend wetting the pile as you make it. (And not just hosing it down after the fact; it’s really not effective.) In our dry climate, as long as we spray dry materials with water when we build, we’ve never had overdrying.
6. Make your pile as porous and even as possible.
The final consideration for ASP is bulk density: you want the right density to air can travel evenly through the pile. To ensure this, you’ll want to include porous materials distributed evenly throughout the pile. For us, this means throwing in a small ratio of wood chips and/or biochar for that porosity. I’d say we use nearly a full 50 gallon trashcan of wood chips/biochar for every 4x4x4 bin. Lastly, you’ll want to mix the materials as you build the pile, rather than stacking in layers that tend to clump and block air. This is good practice for any compost pile to make sure, say, one entire lasagna layer of cut grass isn’t smothering the pile and keeping the layers above it from composting. For us, this simple means throwing in materials evenly together and not in layers. We use leaves, shredded pine needles, woodchips/biochar, and animal manure. When we build
7. Cover your pile.
This keeps in air and smells, and keeps out critters. We use a one-foot layer of wood chips that we scoop off when the compost is ready (and re-use). Some people use tarps. Whatever you use, the idea is to make it harder for air, as well as moisture, to escape the pile.
In this kind of ASP setup, the hot thermophilic stage takes only 30 days. After this, you can turn off the air because the pile has done all the heating it needs to do. Cornell has a good, brief explanation of the stages if you’re interested. After this stage, the compost enters cooling and maturing. It will continue to decompose and break down without added air or turning.
Interested in starting your own ASP compost system?
We’re creating some detailed instructions with cuts and part lists, as well as offering a free hands-on compost workshop in Spring 2022.
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