This post is a little late, considering the temps here in the northeastern US have already dropped into the 20s, but I'm seeing frequent questions via e-mail and the Facebook groups about keeping your herd alive outside the house for the winter.

Of course, I'm making the assumption that you have too many worms to bring in for winter and/or your spouse or Urban Worm Company Logo - vermicompostroomie has vetoed any new tenants indoors or in the garage.

Your situation will vary, but here are some ideas to keep your worms thriving – or at least not dying – until the winter thaw.

Tips to Keep Your Worms Warm

Increase Surface Area

Increased surface area (and even total volume) for your worm container helps cover up a ton of vermicomposting and vermiculture mistakes.  Appropriate pH, temperature, and moisture levels are all buffered with a larger container, ie, it takes a helluvalot more high-acid fruit like blueberries to increase the pH in a 5 square-foot container than in a standard 5-gallon bucket with less than a foot of surface area.

Note: Increasing surface area along won't do much to protect against cold.  But it's a bit of a prerequisite for the following tips.

Feed Them Too Much

Assuming you have increased your surface area, thereby giving your worms somewhere to escape to, then the greenest, most efficient solution is to purposefully overfeed your bin and use the resultant thermophilic (hot) composting to warm your worm herd.  I like the idea of  a trench of composting material running the length of a bed or container or overfeeding in “pockets”.  Once the nitrogen-rich mixture has cooled, it's a prime food source.

As always, beware of overdoing it with the overfeeding as you risk protein poisoning, “sour bin” and other non-heat related issues.  Start slowly and work up from there.

Layer Up

The reason winter jackets are often filled with down feathers is that they are so loosely packed.  It's not the material that keeps you warm.  It's the layers of air within that material that provide the insulation.

So if you have any source of heat you want to trap, creating a fluffy or loosely packed area for the heat to reside will do the trick.  Straw and shredded paper are great sources of fluff.

I recommend NOT soaking these materials as you want to prevent them from clumping.

Go Geothermal

Work with nature, not against it! About 10 feet below the earth's surface, it's a constant 10°C/50°F year-round, no matter where you live.  I am blessed with a barn built into the side of a hill in my back yard.  It's at least 10°F cooler than the ambient temperature in the heat of summer and 10°F warmer in the coldest winter months.  I use the below-grade barn floor and concrete walls to exploit any geothermal effect I can.

I understand you may not have an option like this, but anything to get a couple feet closer to the earth's core will help!

Cheat with Heat

I personally haven't used these but I know some folks swear by them.  The soil cables themselves can be a little pricy, but not as pricy as losing 10 lbs worth of worms.  Heating pads can be placed top – or wrapped around – Rubbermaid bins or other enclosures.

My Favorite: Rope Light Sandwich + Thermophilic Composting

Using roughly 48 feet of incandescent rope lighting layered between two pieces of carpet**, I am able to warm my 3 x 10 ft beds to an average temp of 65°F with some pockets in the 80°F range and the outer edges in the low 50° range where there still seems to be quite a bit of activity.

**It must be incandescent lighting.  Most rope lights these days are LEDs due to their efficiency.  We actually want inefficiency – aka energy loss through heat – with this method.

Here's my method for low-maintenance worm warming

  1. Overfeed the middle 12-inches of the bed with coffee grounds, pumpkin or squash, and even some fresh horse manure (if I'm certain there's no danger of deworming medicine being present).
    • This WILL get warm on it's own, possibly too warm.  So this is why I recommend increasing surface area to give the worms a place to escape the heat.  They find their happy place very easily.
  2. I add heaps of fresh dry bedding over the entire surface of the bed, helping to create layers of air that will trap heat.
  3. Lay a remnant 3×10-ft piece of carpet over the bed.
  4. String or coil rope lighting from end to end.  I'm going to miss some spots, but that's OK.  I'm looking for indirect heating anyways.
  5. Lay another piece of 3×10 carpet over the bed to cover the lights and help trap heat
  6. Leave it for a couple days.
  7. Return to check the temps.  This is a crock pot, not a bakery.  As long as you're not cooking the worms or find them in a frozen block of ice, you're probably doing just fine!


  1. Turn the rope lighting off and let the thermophilic hot composting work by itself for the first 3-7 days.  You may find there's no need for synthetic heat.
  2. Put the lighting on a dimmer switch to better adjust the desired heat.

A note of caution: This technique can dry out conditions, especially if ambient humidity is low and you haven't added any water-laden food waste recently.  The fresh, dry bedding will wick up moisture and the heat from the lights may accelerate evaporation.

I hope this helps!
What has worked for you?  Do you have any of your own techniques?  I'd love to hear 'em in the comments below.

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