Vermiculture outside in winter?

Hi, I live in 5a in the Rocky Mountains outside Denver (7500 ft elevation)- (local nursery down the mountain says I'm 4b but that seems a bit much, maybe that's just to be safe).  

I started my first vermiculture bin this summer and love it.  It would be wonderful to keep it outside in the winter, and I've seen videos from the PNW where people do that, but it probably doesn't get as cold there.  Properly insulated do you think I could compost using worms in the winter?  Or from experience do you think this should be brought inside when it's that cold?

First let me address the USDA Zone portion. Zones are not only latitude and longitude dependent but also elevation comes into play.

If you are located within the boundaries of Zone 5a (this rating assumes an under 1000 ft. above sea level elevation) and you are above 2000 feet above sea level, then your actual zone would need to be reduced by one (5a -1 = 4b to 4a).

Now about worms outside in winter. As long as you can keep the temperature of the growing worm medium above 32 f, then the worms will not be in danger of dying.

In the Denver area this would require some 4 to 6 inches of foam board insulation on all sides and perhaps even a way to introduce some heat as needed, (light bulb or heat tape) but you need to be able to regulate that heat source so you don't cook your worms nor let them freeze.
Most people that live where temps drop to zero f or below are better off bringing the worms into a space that will not get that cold, and use foam board insulation on all sides.
With worms in an enclosed area, you then have the option of using a light bulb for a heat source and since it is mostly heating the ambient exterior there is less chance of cooking the worms in the insulated box.

Thank you kindly for correctly my misconception about the USDA Zones.  I always just looked at the maps which seems to account for elevation (only in that the areas that look mountainous and colder are indicated with lower zones).  It is on these websites where I enter my zipcode it says I actually live in 5b.  But my zipcode goes from ~5200' to ~7800' so I know there must be more to it.  Still at the base level it's considerably above the 1000 elevation you mention.  A local nursery is who told me "up the mountain" was in zone 4 even though according to those maps it doesn't look like zone 4 starts until much further into the mountains....

Thanks for the advice about the worms.  I've read they do best above 50 degrees F but it's good to know they could "survive" until freezing.  Maybe I can put them in the garage and insulated if I want to try that-- at least the wind chill won't be a factor.  Again, thanks

hau Seth, It is more a matter of not enough information given by the USDA than it is misconception by users of their information. I wish the USDA would provide folks their formula for calculating zones, then at least a person could do the math and compare results.

Where I live (as an example of how messed up the zone thing can be) the USDA specifies 7b, but when I do the math the top of our mountain homestead is actually 8a or 8b due to microclimate and wind factors.
I have plants that are supposed to do well in south Florida growing like gangbusters, the only thing I have to do is give them a little protection if we get below 32 f.

Zone information is good to have but I find that you might have a fudge factor of + or - 1.5 depending on microclimate specifics.

Worms work (eat) at 50 f and up, that doesn't mean they die if it isn't that warm (I got that info tid bit from a friend who raises fishing bait worms for a living).

Hallo Seth. Better information than USDA is how deep does the soil freeze in your area in winter. Some local building constructor would give you an answer - he will know it because of safe depth for laying of water plumbing. It is 90 cm ( 3 ft) n our country for example. I live in area, where winter temperatures often drop to -20 °C (-4 °F), but soil rarely freezes 50 cm deep . I made my vermicompost "bin" by digging trench 90 cm ( 3 ft) deep, about 150 cm ( 5 ft) wide and 3 m ( 10 ft) long. In winter, worms survive near the bottom of the trench, where the compost does not freeze.. Do not insulate the bottom and the walls of the trench by some foam polystyrene - the substrate with worms must be "heated" by surrounding not-freezed soil.. You can put insulation on the top of the compost, for example straw bales..
Jan, Czech rep.

Jan Hrbek wrote:Hallo Seth. Better information than USDA is how deep does the soil freeze in your area in winter. .....
Jan, Czech rep.

Thank you, Jan!  Very good to consider. In fact the local water district just buried a pipe on my property which needed to be 4’ deep to prevent freezing. I don’t know if they added additional depth for safety. I take it you aren’t concerned about any worms escaping :)

Eisenia foetida is epigeic earthworm, it will not escape into the soil.. It stays in the compost.. But it is good to put some wire mesh on the bottom and sides of the trench against moles..
If safe depth in your area is 4 ft., than it will be better to dig your trench this deep.. At least in part of the trench..

Bryant RedHawk Is there a type of foam board you recommend for insulation?

Bryant RedHawk wrote:First let me address the USDA Zone portion. Zones are not only latitude and longitude dependent but also elevation comes into play.

If you are located within the boundaries of Zone 5a (this rating assumes an under 1000 ft. above sea level elevation) and you are above 2000 feet
above sea level, then your actual zone would need to be reduced by one (5a -1 = 4b to 4a).

"USDA Planting Zones Map. Considered the standard measure of plant hardiness, the USDA Plant Hardiness Zone Map is based
on average annual minimum winter temperatures. The map is divided into thirteen distinct 10ºF zones, which are further
divided into sub-zones of 5°F."

This is a quote from the Old Farmers Almanac.  I cannot find any info about latitude, longitude, and elevation in regard to
planting zones.  Maybe I'm looking in the wrong place?  Where can I find that info?  

R Jay wrote:  

This is a quote from the Old Farmers Almanac.  I cannot find any info about latitude, longitude, and elevation in regard to
planting zones.  Maybe I'm looking in the wrong place?  Where can I find that info?  

Yeah, I was confused by this too.