Yet for some reason my root cellar stays pretty constant at 5C or 40F.

40 is a nearly ideal temperature for most things

You could rig up some vent fans to bring in outside air when it's cooler, but I don't think it would be worth the effort and expense

 

It's been below freezing for about a month, and there were plenty of night frosts on Oct-Nov when I left the hatch open to allow the cold air to chill the interior.

Yet for some reason my root cellar stays pretty constant at 5C or 40F.
There is no heat but what's coming from the ground.

The ground is frozen now, and there are two, 4" vents in the ceiling wide open.

Nothing is sprouting but I'd like it cooler. Potatoes survived last winter through to about March, by May the shoots were nearly 2' tall.

Any ideas on how to allow it to cool more? Thanks!

Crack the door open a bit?

 

40°F is the ideal temperature. That far North, what you're striving for is to prevent freezing, which would be nice if it stayed below freezing. But the veggies would thaw and then rot. You must be picking up some solar heat.
Is this an earth sheltered cellar? You may be able to insulate the roof, or reflect the sun with light colored foil or plastic.
Just sayin'. I'd be happy with 40° f if that's as high as it went...

 

Interesting, seems a bit closer to freezing was actually ideal. I need to find my Bubel book.

Being completely underground, the roof is the most exposed to ground level. It's is a minimum of 1' deep soil on top. For fear of cold I put down styrofoam sheets on the roof before backfilling. So there shouldn't be much or any solar gain.

 

Interesting, seems a bit closer to freezing was actually ideal.

I really doubt those few degrees will matter, and Winter isn't here yet

 

My root cellar is an old fashioned one built under my late 1860s house, when a person had to count on Mother Nature instead of electricity to move the air. There are screened vent windows with interior wooden shutters on the west and east sides, and plenty of plaster, lathe, and horsehair overhead. Over the 30 years I've lived here and used the root cellar, I find it takes time each fall for the old stones that comprise the walls, and the brick that makes up the floor, to cool enough to help it stay on the colder side. Eventually though, it does. Then I can regulate the temperature by opening or closing the wooden shutters according to the prevailing winds. And over time, the stone helps to limit rapid swings in temperature that can cause freezing or rotting.

I don't know what your walls and floors are made of; but if they're cement, stone, or brick, give them time. A good root cellar is a magnificent thing.

 

40* sounds about right for root crops.
Here is a list of veges/fruits and their ideal storage temps:

http://extension.missouri.edu/p/MP562

 

If you want it lower than 40 you'll probably need more air flow. Do you have a vent that opens at the bottom of the cellar (to allow the cold air to "fall" in, while the warmer air escapes out another high vent)?

Probably the ground at 3-4' down is going to be above 5 C for the whole winter, so you'll be fighting with it to keep the cellar cooler than that. I built one in my house when I lived in Ottawa and I had to be careful to close the vents to prevent freezing, but I think I had good airflow. Also, Ottawa can be pretty cold in the winter.

Now I have one in my basement again. Insulated it as well as possible, but the lowest I've seen it get this year yet is 5 C. I have a fan in the hot air exhaust vent that is on a timer and comes on between 3AM and 7AM. It's just one of those tiny vent fans, but I'm thinking it will help circulate in the fall. As long as we get a real winter this year, I think it will be cold enogh in there for the most part.

Chris

 

I noticed you said you have two 4" vents in the ceiling. Do you have any at the ground level for cross ventilation? Is you floor cement or dirt?

Thanks

 

40 sounds about right to me

 

You don't want it any colder or you risk having your food freeze. I store mine at a much higher temp and have never had a problem with spoilage by the time I use it.

Bob

 

Thermal lag has probably not fully caught up to outside temps.