Why aren't outside temperatures a factor in overwintering plants in an unheated garage?

Hello,  

I'm wondering if someone could answer a question about a ubiquitous statement that seems to come up many times when I read articles on the internet?  This statement always seems to ignore one variable that seems very important to me.

It seems that I'm always struggling at the end of the season to get potted plants into the ground before the freeze starts and I always start thinking about keeping them indoors,  As I read about this I always find those statements about overwintering plants in an unheated garage.  Sounds great, but there is one question about this that no one ever seems to ask.   What zone is your unheated garage in?  I live in Pennsylvania, but I can't imagine that my plants would survive in an unheated garage in Alaska where the outside temp drops to negative 30f.  Why is this never mentioned?  Is there something about being in a garage that negates this?  Just wondering.  I'd sure like to know why the temperature inside the garage and outside the garage doesn't seem to be a concern in these articles.

Maybe a stupid question, I don't know.  I finally have reached a point where I have to know.

Thanks for any replies.  You're all awesome!
Regards,  Tim

For my own outbuildings that I have a thermometer in, I find that the temperature inside the unheated structures are ~20 degrees F higher than the ambient temperatures outside.  I assume this has to do with solar gain during the day, and heat rising up from the ground under the foundations.

I'd suggest that your location in Alaska is likely to be about the same, but maybe your structures will be at ~-10F instead of -30F.

There's a big difference between an attached and an unattached garage. My parents have both, and I don't think I've ever seen ice forming on the on floor of their attached garage. Just ice and snow melting off the cars they pull into the attached garage. I keep my snowmobile in their unattached garage, and it gets cold out there. I'm guessing the walls between the house and the attached garage aren't insulated so that area is able to suck a lot of heat out of the house. Just my guess of why people think that.

For reference a few days when I was in high school they were saying -70F wind chills when it was about -30F outside.(Wind chills affect 60F buildings less than uninsulated 98.6F people, but wind still steals energy from insulated buildings) Typically zone 4, zone 5 on mild winters, and zone 2-3ish on harsh winters.

Michael Qulek wrote:For my own outbuildings that I have a thermometer in, I find that the temperature inside the unheated structures are ~20 degrees F higher than the ambient temperatures outside.  I assume this has to do with solar gain during the day, and heat rising up from the ground under the foundations.

I'd suggest that your location in Alaska is likely to be about the same, but maybe your structures will be at ~-10F instead of -30F.

Thank you Michael,  This is good information.  I seem to hover around a difference of 15 degrees, but there is a long gap right at the joint between the concrete slab and the side wall of our garage.  I'm sure that a lot of cold air enters there.  I just realized that I should fix this since our house is connected, and this would make the house a little more efficient regardless of storing potted plants or not.

I actually don't live in Alaska.  I just create poorly written posts in Central Pennsylvania and have to go back and edit them several times before they make sense.  I was looking for the most extreme example that I could think of and picked Alaska as my example.  I went back and changed my post a couple of seconds ago so that it made more sense.  Thank you.   It would be interesting to know what happens in a garage in Alaska though.  I somehow doubt that there is much plant storage there.

Thanks again!

This reminds me of recipes and things calling for 'room temperature' as though we all have 70F homes.  It throws me every time because our winter 'room  temps' are anywhere from 40-60 degrees F and summertime even more variable, from 50-85F.

No central heating or air.

Peter E Johnson wrote:There's a big difference between an attached and an unattached garage. My parents have both, and I don't think I've ever seen ice forming on the on floor of their attached garage. Just ice and snow melting off the cars they pull into the attached garage. I keep my snowmobile in their unattached garage, and it gets cold out there. I'm guessing the walls between the house and the attached garage aren't insulated so that area is able to suck a lot of heat out of the house. Just my guess of why people think that.

For reference a few days when I was in high school they were saying -70F wind chills when it was about -30F outside.(Wind chills affect 60F buildings less than uninsulated 98.6F people, but wind still steals energy from insulated buildings) Typically zone 4, zone 5 on mild winters, and zone 2-3ish on harsh winters.

Thank you Peter.  That all makes sense since you mentioned it.

I'm actually thinking of making some sort of a box next to the side of the heated wall which also has a heated basement under it.  Not sure how I would do that yet since I have several trees which are now over 6 feet tall.  Maybe just a lot of loose mulch on top.

Funny thing about the wind chill that you mentioned......  I used to work for a company where the wind blew pretty hard across the adjacent fields connected to our parking lot.  My supervisor was super-nice, but he sure didn't want you to park the company truck facing the wind.  His reasoning was that it would make the truck freeze up on the cold winter nights were it would sit idle for two shifts.  It didn't have any block-heater or any active heat device for the wind to suck away warmth over nigh,t and the heat from running the engine was gone in less than an hour, so the truck cooled to the actual outside air temperature very quickly, regardless of which way it was pointed. He was sure that the truck would get colder than the actual air temperature because of the wind.   I knew that there was no sense in saying anything different because it was one of those arguments that you knew that you couldn't win.

Michael Qulek wrote:For my own outbuildings that I have a thermometer in, I find that the temperature inside the unheated structures are ~20 degrees F higher than the ambient temperatures outside.  I assume this has to do with solar gain during the day, and heat rising up from the ground under the foundations.

I find this true as well. The difference can be 5-10C.

Regarding plants, the other factor is that's it's a sheltered and consistent environment. No wind and sun to suck away moisture and "freeze dry" the plants, and limited exposure to the radical freeze/thaw cycles we've had these last winters. These things kill perennials.

Judith Browning wrote:This reminds me of recipes and things calling for 'room temperature' as though we all have 70F homes.  It throws me every time because our winter 'room  temps' are anywhere from 40-60 degrees F and summertime even more variable, from 50-85F.

No central heating or air.

Same here   I'm with you.    For the first time in my life (this year) we've moved into a house with both central heating and air, but for the last 40 years I've been acclimated to the outside temp and I'm able to go outside regardless of the temperature and get a little done.  I plan to keep our inside temp tracking as much with the outside temp as much as my family will allow.

I'd like to make another post called "why does the inside temperature get so hot in the winter and so cold in the summer?"