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Winterizing Your Outdoor Bin

Depending on your climate, insulating and/or heating  your outdoor bin during the winter months is necessary to keep your worms  active & eating optimally.  I highly recommend that you monitor the bin temperature by inserting a compost thermometer into the side of the bin.  I use one with a 19″ stem (approx. $20), though a 5″ stem, costing only $7, might work as well.  Drill a hole, the same diameter as the stem, where the stem will enter into the center of the bin.optimum-worm-temps-11

If you use soil warming cables (described below),  place the thermometer stem a few inches above the cables, because you want to make sure no area is getting too hot.

Here’s a graph showing optimum temperatures for worms.  It’s to be used only as a general guideline, as I compiled this from several sources, not all of which agreed exactly.  You can download this graph, print it, & keep it near your bin for reference.  Right-click on the graph, select Save Image As, & it will download.


Though it’s always a good idea to keep a 2-3″ layer of leaves on the surface of the bin, it’s especially important to do so during the cold winter months.  The seasonal timing is perfect; leaves are most plentiful just when you begin to need them.

You can also attach rigid foam insulation board to the sides of your bin.  I use 1.5″ board.  Or place straw bales around the sides.  I’ve not tried this, but as long as you can keep rats & mice from climbing on board, it sounds like a great idea.

Soil warming cables

For the past two winters, I’ve successfully used Gro Quick Soil Warming Cables from Wrap-on Co.  I’m not sure if heating a worm composting bin fits within the manufacturer’s intended use or not, so before buying, please read their installation pdf, with their warnings & cautions.  That said, my experience has been positive.  I would not rely on the built-in thermostat, however.  I nearly cooked my worms on one occasion.   Since then, I’ve used a timer to maintain the desired temperature.

Where I live in northern California, night time temps below the mid to upper 20’s F are unusual.  In such a climate, if you regularly feed your worms, and are using an insulated 50-60 gal bin, I doubt the bedding temp will ever fall to a live-threatening sub 50 degree F.  But the lower the temp, the less they eat.  In my experience, after installing soil warming cables, there’s no longer a winter slow down.  I can add scraps at the same rate in the winter, as summer.

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