Yes

any size container will freeze. i have a 1/2 wiskey barrel with a hydrangea in it that froze. i have 5 100 gal containers that freeze solid.

I have occasionally had a plant survive in this zone, but usually it is a herb like oregano or lemon balm and the container has been placed up against the building with snow covering it all winter giving it some warmth and insulation. I have thyme and chives that survive in large cinder blocks farther away from the building, but the bottoms are open to the ground.
Maybe you could make a 'holding spot', like a temporary raised bed where you could set the plants and bury them with mulch or compost, they might survive? Don't nurseries do that?
I've got a couple of tiny rugosa roses that I'm thinking of doing something similar with. I started them from seed and I don't have a permanent spot for them yet.

Thanks for the info. I know its probably a very basic "newbie" question.

Would a very dark and cool (but not freezing) basement be okay or should I bring them into a living area with more light and warmer temperatures. Not sure what would be best for their normal winter cycle. Thanks again!

I don't think that they will need light or warmth. If they were planted in the ground they would simply go dormant and then come back up in the spring. However, they should be in a warm enough area that the pots don't crack.

I tried to leave pots outside through the winter once and several cracked. Last year I put them in our shed, but covered them with old sheets and rugs for warmth.

Perennials and maple trees HAVE to go dormant, or they won't last very long. The winter cold period is essential to them, because it is part of their growth cycle. If you bring them inside where it's warmer than around 40 degrees, they will not go dormant, and they MUST go dormant. Any containers that are above ground will freeze through outdoors. The best thing to do would be to bury them in the ground, but that's a pain. Otherwise you need a coldframe type environment, somewhere that ideally would be in the 30's. Your plants don't need light in winter though, so an unheated garage could work.

Joe

No light necessary during dormancy or quiescence. Ideal over-wintering temperatures for most temperate plants are 32-42*. Allowing temperatures to rise above 42* for more than a few days will stimulate the plant to growth, which will reduce cold-hardiness dramatically. The best strategy for plants that normally go dormant is to keep them as cold as you can for as long as you can into spring to retard early leaf-out. Plants deprived of a dormant rest will often go dormant unexpectedly at any time - even in mid-summer. This is normally fatal. Those plants deprived of a dormant rest that do survive the subsequent growth cycle usually grow very weakly & lag well behind their counterparts that DID have a cold rest.

Mother Nature knows best - follow her lead.

Al

Great. I absolutely appreciate all the responses.

Al,

I have five young JM in one gallon containers that I have in a fairly protected spot in the back yard. Our temps are dipping into the 20s overnight and I am thinking I need to bury/move the pots to prevent the roots from completely freezing. I am in zone 5 (central WA). If I understand you recommendation correctly, I should not move my containers into my garage since it seems to maintain temps around 55f? The garage is unheated, but insulated very well and the gas furnace seems to do a good job at keeping the temps higher than I ever would have expected.

I'm wondering if I should bury the pots on the north side of the foundation and cover with mulch as you have suggested until the spring.

-Troy

I would ..... (bury/mulch). If the plant is on the ground, the small amount of (geothermal) heat from the earth will moderate soil temps from ambient air temps somewhat, but not more than about 5*. I think you're probably going to start to lose a significant volume of roots as the actual soil temps approach 20*. The nursery trade has established 14*F as the killing low cut off for Acer p's, but that means that ALL the roots are compromised by the time that temperature is reached. The finer & more succulent roots begin to succumb to cold injury at temperatures as warm as 28*, so you have a vested interest in trying to keep those root temperatures up around freezing to about 42* for as long into the spring as you can. Moving them into the garage overnight won't hurt, but those extended stays (several days) at temps in the mid-40s or warmer is going to stimulate growth and dramatically reduce resistance to cold.

Al