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It’s cold and wintery out there. Great time to grow microbes.

Updated: Dec 27, 2019

Microbe production, single-yard piles of composting material. Controlling moisture during winter.
Supporting your protective tarp so it peaks, and sheds water, can be important for winter microbe production.

Yep, winter is here. With its cold, and rain, and snow. One might be tempted to take the season off, expecting these conditions to make microbe husbandry difficult.

One would be mistaken. Winter can be a great time for multiplying the microbes stocks we may need for the coming season.

Yes, adjustments will be necessary. Organic-material proportions need tweaking in colder temperatures – namely, more nitrogen-rich materials for stronger bacterial growth and greater heat production. And yes, if your location is such that it won’t top freezing for long stretches, you may require a protective structure (this is generally of higher importance in summer, when heat can easily become too intense for proper composting without shade).

There are several wintertime factors that offer advantages to our microbe-reproduction efforts. Colder air (or water) holds more oxygen, so it helps maintain aerobic conditions throughout a cooking mass of material.

And of course there’s relief from the high ambient heat of summer. It’s nice to be free of the problem of quick moisture loss. When working in the heat, we try to compensate by misting our piles from the outside, but it’s risky – easy to create overwatered pockets with anaerobic activity and the resulting nutrient loss. So it’s a big help when moisture sticks around for a while.

But having said that -- yes, there’s a trade-off. In winter, moisture works by different patterns, and they can be tricky. If we’re working outdoors in a relatively unprotected environment, we keep our piles covered for two reasons: to keep rain out and heat in. It’s easiest to use a tarp, but the tarp brings its own issue: condensation. As microbes generate heat in the pile’s center, they respire moisture that is carried upward, to gather under the tarp. Some of that gaseous moisture condenses against the tarp’s cool surface, and soon drops back to the pile. The result: your material is too dry in the center, but too wet in the top few inches.

It takes some practice to maintain optimum moisture through the two-week thermophilic (high-temperature) period of microbial growth. Bulk operators, who produce material in windrows, sometimes use covers made of a canvas-like material that sheds water while allowing some breathability.

In a single-yard pile, we create a similar moisture-shedding system using a tarp, a length of pipe, a rag, and a bungee cord. Insert the rag partway into one end of the pipe (this is to cushion the tarp), then insert the pipe vertically into the center of your pile. Drape the tarp over the pipe to form a peak. To secure it, wrap the whole thing with the bungee cord, about a third of the way down the pile.

To vent moisture, add a chimney. Take an edge of the tarp and pull it outward, creating a ridge that extends in a straight line, to a guy wire and then a stake in the ground. The chimney serves two purposes: it guides condensed moisture down the tarp, so it drops to the ground; and it allows release of steam, so all that moisture doesn’t wind up soaking back into your material.

Growing microbes is like cooking: there are recipes and directions, but there are also nuances. Controlling them can take practice. Experiment with these techniques. Get the hang of the squeeze test. Add an extra chimney, switch up your ingredients. Keep records and monitor results, and soon you’ll have a full soil food web, ready for re-introduction to your growing system.

Stay warm out there.

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