harvesting seeded eco-compost

Here at my apartment, there is very limited space for a composting system. One way to create compost in such a small space is to use a set of waterproof, decay-proof plastic tarpaulins to contain and control the process. On the upstairs deck is an ecosystem-based “low and slow” compost pile designed to produce rich, seed-packed eco-compost, an integral part of all of the eco-gardening projects.

“Low and slow” means that this compost system works at a relatively low temperature and takes a fairly long time to fully process its “food.” One reason it is low and slow is because it’s fairly small, so it can’t attain the high temperatures needed for fast composting.

Another reason it’s “low and slow” is because the process of ecosystem composting is fascinating to watch, and I like to let it develop through a whole ecosystem cycle before disturbing it by turning it over. The center of the pile develops more slowly than it might, because oxygen does not get in there very frequently.

It’s time to turn the compost!

In the picture above, the tarpaulin has been opened out and weighted with some bricks. A second one has been inserted at the left side, with its edge underneath. This one will receive the material from the pile as it is turned and mixed.

Above, I’ve started pulling away the loose, dry plant material from the top of the pile. I usually just casually toss plant clippings onto the top, letting them dry out naturally. They contain the precious seeds that will become such an important ingredient in this eco-compost. Unlike traditional “hot” composting systems, this eco-compost pile is deliberately designed to preserve the plant seeds that end up in it. We want the seeds to sprout when the final mixture is delivered to the garden.

One important note: I’m using a four-tined sharp-ended claw tool, which seems very eager to rip big holes into the tarpaulin. I must be careful! I do not want to destroy the tarp’s waterproof properties, so I use the claw tool very gently, angling it so that the tips do not injure the tarp.

Above: The dry plant matter is brought over to the receiving tarpaulin (off the left in this picture) where it will soon be covered up (and moistened!) by the remainder of the compost pile after it is sifted. Now the darker, moist “core” ecosystem is exposed. This is where most of the decomposing action happens. It’s loaded with many kinds of critters like worms, sowbugs, springtails, mites, nematodes, centipedes, fly larvae, and much, much more.

Worm tracks are visible on the tarpaulin where some of the core has been moved away. They are in there, and it looks like they are fairly large too.

Now the exercise begins. Yes, tarpaulin composting (the way I do it at least!) involves some labor. The first few shovels of core compost are on the sifter and I’m ready to get a little bit sweaty!

On the left, the first bit of sifted compost.

On the sifter is the first batch of material to be dropped over the dry stuff that was pulled away from the core. This large debris is mostly bits of woody stems, chicken bones (yes, this composting method can take animal products), chunks of eggshell, and a few foreign items like fruit labels and small stones. It gets returned to the flow for further breakdown, after I pull out the worst of the foreign items.

On the right, the rest of the unsifted core.

Above: the good stuff! Freshly sifted compost from the active core of the pile. Heavily laced with a wide variety of seeds from all sorts of interesting plants, moist and loamy. What an amazing, rich, sweet aroma it has.

After sifting about half of the core, the remainder of it is shoveled onto the top of the destination pile, and the tarp is dragged over to the spot where the original pile was. The edges get rolled neatly and weighted with bricks, and the pile is groomed into a nice clean shape. But we’re not done yet.

Above: On the right, finished, sifted, seeded compost. In the center, kitchen scraps from our own kitchen and those of several neighbors. This is the rich “food” that enlivens the compost pile and makes it more than just a tangle of dead, dry plant stems. On the left, a bucket of Just Plain Dirt collected from various different places. It contains many kinds of seeds, including those of plants that are not yet part of the garden.

Above: The bucket of kitchen scraps is inverted over the top of the compost pile, revealing hundreds of large fly larvae that were crowding the bottom of the bucket. These are larvae of black soldier flies (Hermetia illucens, read more in this Wikipedia article).

UPDATE: here’s more about black soldier flies, with a great picture of a gravid female.

Black soldier flies are not only quite common here in California, they are among the best and fastest compost decomposers, whose larvae have absolutely ravenous appetites. Were it not for the soldier fly larvae, this freshly dumped bucket of kitchen scraps would have been four or five buckets – that’s how fast they eat vegetable scraps and convert them into … well … themselves, and a layer of rich, black, loamy waste. They work so darned fast that the kitchen scraps in this bucket rarely have a chance to get moldy or smelly.

Now that the bucket has been dumped, these fly larvae will dig themselves in and pupate, emerging as flies within a week or so. The adult flies and larvae are wonderful food for birds (bluejays, juncoes, and mourning doves frequently scratch around in the compost looking for them) and contribute to the local ecosystem’s diversity and health.

In the last picture, a couple of shovels of dry neighborhood dirt have been roughly dumped on top of the upturned deposit of kitchen scraps. I’ll spray the compost pile down with a bit of water, and my morning exercise session is finished. Yeah!

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