February 10, 2015

Compost House

A key element in running a bigger garden is dealing with larger amounts of compost and other bulk materials like hay and mulch. I'm enamored with the no-till, compost heavy methods espoused by Lee Reich in Weedless Gardening, and plan to use that approach as a starting point for how I manage our growing areas moving forward.

Our old compost got cleared out when we renovated the backyard, so I could start with a fresh slate. I tried to envision a user friendly, easy to build system sufficient for our newly expanded gardening ambitions.

Over the last 10 years we have tried a few smaller scale compost solutions. The compost was originally set up by our housemate and good friend Alexi Arango,

He took meticulous care of it while he lived with us. When he moved on, I inherited stewardship of the compost, and have been more neglectful of it than Alexi.

First came a black plastic hut thing from the city called the Earth Machine. Actually we got two of them, one to accumulate in while the other was finishing. They don't really last all that long. Eventually they start to crack, then the two halves can't stay together. The first one had to be retired after only a few years of service, injecting several kilos of plastic into the city waste stream in the process. On the second one the flange keeping the bottom hatch on cracked free. Lastly, a rat or squirrel chewed a big hole in the side. It was more than ready for the trash by the time we removed it for the renovation. The capacity was ok for coping with one vegetable loving household, but it was not really big enough to take much extra material from our garden or anything imported from outside.

Alexi purchased and set up a Compost Tumbler after the first Earth Machine fell apart (partly visible to the left in the above photo). This design appears promising because it makes turning the compost very easy. However in practice it was less than satisfactory. Even at what seemed like reasonable loading, the thin mild steel sheet metal that forms the drum would get deformed and dented, making the hatch not fit properly. It was also clear that the sheet metal was going to rust through in not too many years. But worst of all was the fact that the teeth on the plastic pinion gear attached to the handcrank cracked off early in it's life, rendering it just another static receptacle for compost. Without a functional crank, it became annoyingly difficult to get compost out of the drum or to turn the drum around. These things are not cheap either. I don't know, maybe it would be fine if you didn't produce too much volume of scraps.

The last issue I had with the Compost Tumbler was that it was not as friendly for worms. One year Alexi got some compost worms, which really revolutionized the compost. Before, the pile would often stink to one degree or another (probably from us being insufficiently diligent about turning it, or not interspersing enough fluffy carbonaceous material). It also took a long time to break down. For the most part we add to it only slowly, about once a week. This makes it tough to have a hot compost pile, so we are relegated to slower and colder avenues of organic breakdown. But the worms were incredible. When a new bucket of slops was added, they would largely devour it before you opened the lid to put the next one in a week later. There were fewer smell issues, breakdown was rapid, and turning became kind of optional. It was not as sensitive to how much carbon material you added with the veggie scraps.

The worms have never been as fabulous as that first season, but we do have lots of worms in the compost, or at times grubs. Depending on the season, temperature, and slops loading, there can sometimes be a ~5cm thick layer of glistening, seething grubs on the top of the compost. If you put your head close to it, you can hear them all moistly squirming around.

 I don't know what the story is with the grubs, or if the worms we get at other times are descendants of the original compost worms, but in any case invertebrate life is crucial to accelerating breakdown and making less work for the humans.

The Compost Tumbler is elevated from and divorced from the soil. This makes it freeze quickly in the fall, with greater temperature swings during the season. Additionally, worms can't shelter in the soil during the winter and recolonize the compost in the spring. I kept the compost in the tumbler (relocated to the side yard) during the backyard renovation and over the winter. But as spring was beginning to set in, it was time to figure out a better system.

We do have rats, skunks, and other animals around that are interested in getting in the compost. So I wanted something that would provide some resistance to animals, and which I could repair as needed. While we have a lot of space for the city, we don't have a lot in absolute terms, so we favored concepts which would keep the compost from sprawling out. We would be spending a lot of time right next to the compost engaged in other activities, so we wanted it to look tidy and to keep the stink down.

All the zillions of possible layouts we worked on for the back yard all included a substantial space for the compost. But we were not 100% sure where to put it and how big to make it. So I decided to just build something out of cheap locally sawn rough cut pine. This is a low investment in materials cost, and it won't last all that long. When it is rotted and needs rebuilding we can revisit our decisions about placement, size, and design. I drew up a cute plan in autocad with a gable roof and four bins, with the idea of one roof plane being able to hinge up on each bin. The four bins would each have about a meter square footprint. This would give me one for accumulating compost, one for finishing compost, one for hay storage, and one for storage of cut up sticks or maybe mulch.

I ordered the lumber for the design, along with wood for some garden paths and the borders of the experimental grain maze (more on that in a future post). The wood was supplied by Brightman Lumber company, and I had them deliver it to my driveway. Basic cost for 25mm thick boards was less than $9 per square meter ($0.80/bf). Nice!

One thing I hadn't counted on was that the wood would be fresh cut and not at all dry. Let me tell you that moving wet 4m long 2x12 wood is no picnic. Even the 1x boards for the compost house were deceptively heavy. I had some concerns about building with wet, green lumber, but I really needed to get the compost houses built, so I just went for it. Things did shrink as the wood dried out over the summer, but it has not yet caused any serious problems. The wood was fairly pitch-ey, which made for gummy hands and gummed up tools. But the low cost and very short lead time is pretty compelling so I would probably do it again the same way. Everything is fastened with stainless screws, which I can remove at end of life for the structure.

Building commenced in freezing rain in early spring, in the mud pit that was the back yard at the time (grass was just seed at this point).

As I started building up the structure, it looked awful large. We realized that the gable roof was going to look too huge, and would obscure our view of the west side intermediate terrace from our kitchen windows.

So I modified the design to be a sloped shed roof, at a lower level. This was easier to build anyway and left me with some extra lumber for other projects.

Each roof hatch has a galvanized handle, and swings on galvanized hinges. Each has a piece of chain secured on either side by a lag screw to prevent the lid from opening too far. While the structure was in place in early spring, the hardware wasn't fully installed until almost autumn.

I'm curious to find out how long the green pine boards will last given that they are in constant contact with wet compost in one of the bins. But if it is only a couple boards that are bad, I can just replace them as needed. If the whole structure degrades too far, as it must do eventually, it can be composted and rebuilt. Even if it went in the landfill, at least it is renewable and biodegradable material. If it needed to be rebuilt at the right time, when we someday renovate the front yard, I could cut up and bury the remaining wood in the new beds for hugelkultur.

The way I did the front walls, with removable boards in grooves, is working out well. These are easy to put in and out and make it much simpler to load stuff in and out of a bin with a shovel or fork.

Compost Supply
The amount of compost we generate from kitchen scraps is too small for our ambitious gardening plans. I read this book last month from the library, and I love the idea of composting our poo in the back yard:

The book was a great read, mind expanding, and very inspiring. If by chance you have a slate roof, also check out the amazing Slate Roof Bible, by the same author.

If we just composted our poo, we would have plenty of awesome compost every year. And it would make our pile thermophilic, allowing us to compost a higher portion of organic material from the house more fully and quickly. But for a family our size, we would need way more space for compost piles, and would have to get carbonaceous material delivered in bulk, which would need to be stored somewhere. And despite Joseph Jenkins reassurances and numerous testimonials in the book about how it can be virtually zero odor, it is hard for me to believe I could be dumping a bucket of poop slops in the backyard every day or two and not have some unpleasant smells. In our relatively urban setting, we have ~12 other people living in close proximity plus many passers by, and not enough space to move the poo compost away from where people hang out. Spending a couple hundred dollars a year on compost delivery is far easier and will lead to less friction with the neighborhood, even if it is morally bankrupt compared to composting poo. And even if it is a bit of an illusion built on trucked in organic material, the idea of having the back yard filled up with interesting garden features and food plants sounds more charming than having it in large part devoted to systems for digestion of human waste. But who knows, that calculus could change if times get tough!

Last spring I got 2 cubic meters of compost delivered from Cambridge Bark and Loam. This load went to fill up the new grain maze beds,

to top off old garden beds, around newly planted perennials,

with the remainder being spread out over the future lawn area.

We had an intern from Japan named Masa staying with us for a month last spring, and he was happy to help plant the apple trees and spread compost. In the background of the above picture, Violet is in mid-air during a jump off into the hay bin.

The new back lawn soil was partly subsoil, having been scraped off for regrading during the renovation, mixed with a little SuperLoam from LSX. The soil test of that area revealed that it was low in lead (boo-yah!), but low in nutrients and organic matter.

I don't know how much the cubic meter of compost spread in the area helped, but the lawn came in extremely well over the summer.

The lawn is a clover/grass mix from EarthTurf, with the grass dominating in the spring but the clover dominating after that. I don't mind clover; it looks lush, mows easy, and it soft to walk on.

In the fall, I had another 2.5 cubic meters of compost dropped off in the driveway from Landscape Express.

Both the Cambridge Bark and Loam and the Landscape Express products are rather woody. The CB&L stuff had more trash in it, like old drinking straws, etc. I guess I prefer the LSX product slightly, but there probably isn't a ton of difference. It almost certainly needs extra nitrogen for use on veggies, which I can supply via seed meal or blood meal. The plus side of it being woody is that it is kind of it's own mulch.

The fall delivery of compost went to frosting the micro-orchard

 and most of the intermediate terrace. I'll compost the strawberries in June after harvest. They were still going strong plant-wise at this time so I hesitated to bury them in compost.

Some went to frosting the grain maze and berry bushes planted last spring.

 I put some in spots I expect to plant more perennials next spring, and the rest went into storage in the compost house for use in the spring.

So far, the compost house has been fantastic. Plenty of room for kitchen compost accumulation and aging. Plenty of room to store salt marsh hay, of which I have brought in 5 bales in the last year. The kids like jumping in the hay bin. At least until it becomes compacted and moldy.

And it provides a kind of convenient counter-like surface in the yard for various tasks,

like chopping up these sunflowers blown down in a summer thunderstorm.

It could be a case of stuff expanding to fill the space allotted to it, but all four bins are presently filled up, so I'm glad I made it as big as I did.

Deep Freeze
In the Boston area, we have had record amounts of snow recently, almost 2 meters in the last month. The compost house is now completely encapsulated in a snow bank. These couple pictures were before the latest storms.

We dug some snow caves in the drifts, one of them terminating in at the hay side of the compost house.

This is what the compost house area looks like now, after more snow. Even more expected in a couple days.

 Going to have to dig the kitchen accumulation bin out again this weekend so I can dump a new load in it.


SJ Kurtz said...

Composting tumbler needs it to be warmer to work completely, and by then it's self-destructing. Better to rebuild a pine bin set every couple of years and use worms; you end up moving the bins around and improving the area under them as you move around. It's the long game, but you'll like your results better.
Nice tunnels! We've been wondering how your people are doing with the snow we are missing in Washington State.

SunGold said...

Your compost house is a thing of beauty and your kids are insanely fortunate to do all this with you.

But, when I saw the headline, I had an absurd picture of a tiny outbuilding that had composters inside. I imagined it cozy, warm, and filled with that good-earth smell. Kinda funny, when I think about it. Maybe I have to make one for myself!

Holly Gates said...

@SJKurtz - Wish we could send some of the snow to your side of the country; I think we've had enough here!

@SunGold - I've seen a number of discussions on permies.com about using compost pile heat to warm a dwelling... maybe you are on to something there with a compost pile in the house ;)

Elle said...

Exactly the kind of compost structure that we use in our community P-Patch here in Seattle, except that ours is a three-bin system and the wood is cedar.

Bob Gates said...

Veryu good and cool project. Good for kitchen waste, for soil, for kids, good all over.
Nice family project.