For potted plants that overwinter outdoors, the general rule of thumb is to select plants that are hardy to two zones colder than your own hardiness zone. In other words, if you live in zone 7, be sure that your potted plants are all hardy to at least zone 5. So, your cherries will probably be fine, but a little added protection wouldn't hurt. For example, you could bury the pots in straw, wood chips, leaves, etc. to insulate the roots. Alternatively, if you have an unheated garage that stays under 45 degrees or so, that's a good option if you expect unseasonably cold weather.

This post was edited by shazaam on Sat, Jan 4, 14 at 8:07

Sorry, I can't answer for your varieties and your zone. Hopefully someone else will.

You can improve your chances by insulating the pots. I bury my pots in leaves. I pile the leaves a few inches above the rim. They settle a few inches below the rim.

I live in zone 5. I have overwintered the following fruits in pots buried in leaves: sweet cherries, mulberries, gooseberries, blueberries, and plums. However, I have only been doing this for a few years. The forecasted cold spell will be the coldest they've been subjected too. (-10 degrees) I am concerned. If I had to guess, I'd say that your cherries will survive 9 degrees if they are fully dormant and if the pots are insulated. Probably even snow would be better than nothing. But it's only a guess.

Depends largely on how many of the roots are pressed right against the inside of the pot.

Essentially, you just need to protect the soil in pot from freezing through the sides. In nature the soil freezes from the top so deep roots are not affected too much. You can protect the deep roots by wrapping the pot in insulation and/or maybe just a plastic bag or two.

Thank you for your responses. I just let them sit out when the temperatures are in the mid 20's to 30's but when it gets down to the teens, I bring them inside for a day or two until the temperature rises around 25 - 30 degrees. They are fully dormant and there are no roots pressing against the sides of the pots.

I am wondering what is the temp of your garage?

Olpea posted interesting article on another thread (hope it's ok to re-post):
read here
about hardiness of fruit trees; I am referring to changes in temps in regards to trees.

I don't grow fruit trees (yet), but overwinter many potted perennials in pots with the added protection of leaves as mentioned above. I believe that well draining soil is very important in pots too.