Compost Maintenance: Aeration and Moisture Control


Compost care is getting ready to get ready. The weather here in Arizona is warming up and our green thumb is starting to itch. It’s time to GARDEN!!

Although the weather in the southern United States may be warmer now, the soil is way too cold to do much productive work. So, we will work out our need to be doing something in the garden by tending our compost pile. For some of you in other latitudes, this itching green thumb will have to wait a bit; but for us, the time to scratch the itch is now.

After a cold season of settling, compacting, and being worked on by the little microbes, the pile is ready for turning. What began as tomato vines, carrot tops, bean bushes, and other great garden trimmings is now a soggy, brown mass with the odd vine piece still recognizable Category. We found that the last storm wet our pile pretty thoroughly and that the activity of the microbes is sluggish at best.

Compost needs to be moist and warm for optimum working on the part of the micro-organisms and bugs that cooperate to make the “black gold” we dig into our garden beds for next season’s crop. However, compost doesn’t like to be wet and soggy. So today we turned the compost from one bin to another and stopped when we had transferred about half the material.

We left the piles uncovered to allow our Arizona sun to evaporate some of the moisture and bring the “feel” of the compost to moist rather than wet. Compost that is too dry inhibits the microbial activity necessary to create compost. Wet compost goes “anaerobic”, it doesn’t breathe, and the material just rots and smells bad.
A variety of companies offer tools such as a moisture meter to keep track of compost moisture. For those who don’t want to bother with devices, we suggest that compost that has the feel of fresh bread crumbs – moist, soft, and spongy – is just about right.

We prefer a three-bin system. One bin is for new material, one bin is left empty for turning compost, and one is reserved for maturing compost. We fill and cover one bin that contains the vegetation from fall garden cleanup and add kitchen trimmings, coffee grounds, tea leaves, etc. through the winter. We turn this bin into the central empty bin as needed to aerate and regulate moisture, perhaps once per month. After the turn of the year, as the weather warms up, we begin a new bin and let the full one finish off, moist and warm, until it’s time to screen it and dig it into the garden beds.

For urban gardens and small rural gardens, a variety of manufactured composting devices are available. They range from tumblers on a stand to stacked boxes to simple slatted wooden crates. Sizes range from small kitchen scrap collectors holding about 3 quarts (about 2.8 liters) to 400 gallon bins (about 1500 liters).

Our compost system is three bins, each 4 feet wide x 4 feet deep x 3 feet high or about 1.2 meters x 1.2 meters x.9 meters. This provides about 48 cubic feet (1.36 cubic meters) of compost volume. We now feel that ours is a bit large and would build our next bin system with three bins each 3 feet (.9 meters) each direction.

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