I'm also in zone 5, but I admit I don't have a feel for what winters in Utah are like. I don't have many things in pots to begin with, but my mom has successfully overwintered small trees and shrubs in pots, but she dug them into the soil the depth of the pot. The tops of the plants (if appropriate to the zone) change their chemistry to handle the cold, but the roots are used to the slightly warmer underground temps. My mom used those thin plastic pots from the nursery. I'm sure pottery (ceramic) pots would crack and break in the cold.

So, basically, I've never done or heard of anyone here in SE Michigan overwintering things in pots above ground. It's too cold and then warm and then cold (variable) here. :)

Have you tried posting this on the container gardening forum? I'd say that selecting appropriate pots or cotainers is the least of your worries, as your winter cold will put pretty much everything at risk.

FWIW, plants suited to long term container growth should be selected based on hardiness of at least one full zone (preferrably 2) colder than your regular climate, as that is the effect they will have to endure in a containered situation. That limites your choices to plants with a hardiness of zone 4 temperatures, better with zone 3. Size will have a significant bearing as well - the larger the container, the less likely the soil in it will freeze solid in winter.

As for containers, wood will withstand winter cold better than any ceramic pot, but there is a large selection of frostpruf glazed pots originating in Asia that are totally winterproof, at least in my climate. Concrete aggregate should winterize well also but is heavy and very expensive and typically only available to the trade, as they are primarily used in commercial settings. Avoid terra cotta and plastic as neither will withstand freezes for long (terra cotta spalls and plastic cracks).

A good quality potting soil - never regular garden soil - should be used, as garden soil is too heavy and doesn't have sufficient drainage. For long term container growth of trees and shrubs, I use a potting soil recommended specifically for them, as their needs are different than those of annuals or perennials or other, faster to mature plants. Adding some coarse, barky compost to regular potting soil will work if your choices of specific potting soils is limited. And always include some slow release fertilizer at time of planting. You will needs to supplement this as time goes by, as the watering requirements for plants in containers will leach any nutrients rapidly out of the soil and they will need to be replaced.

Ha! I'm funny! I posted earlier that "So, basically, I've never done or heard of anyone here in SE Michigan overwintering things in pots above ground."

Well, it turns out I inadvertantly left out a clay pot (wider and more shallow than the standard kind) of hens and chicks. It is close up to my house and, more importantly, has my porch as a wind barrier to the sw so it's quite sheltered. It's been off and on covered in snow and I just "found" it the other day. The pot itself looks fine; not cracked or broken. The hens and chicks look black but I know they're hardy in my zone and I hope they come back. Will report later in spring on their progress!

Monica

Will try this post on the container forum (missed seeing that forum) Thanks so much for the info, everyone!!!

I have seen the same thing happen as you Monica ....and the microclimate of where it's sitting is pretty important, I think. Other than that, I have only seen those really, really large concrete containers that can hold a lot of soil actually be able to overwinter small evergreens or perennials. In a small typical pot, I have done as GardenFaeires' mom and sunk them into the ground. That definitely works....it's just a pain depending upon how many you've got , how large they are and whether you have the garden bed space to do it!

I too left hens and chicks outdoors in a pot on my front door stoop. Survived last winter, this winter they are covered with a foot of snow that has melted somewhat and re-frozen into ice. Hope they make it to spring.

I have many containers in and out of my garden.

I had 32 gallon rubbermaid containers as large deep beds between my arch-trellises.

I had 21 gallon rubbermaid (might be laundry or toy basket, round with rope handles) with plantings.

I had 13 gallon rubber/plastic trash cans (kitchen type)...

...and tons of various planter pots etc...

and several terracotta planter pots.

This last winter's ice storm demolished everything. All the tubs are trash. Cracked, falling apart, from the cold. The terracotta pots actually *shattered*, took me eons to pick the pieces out of the soil.

So if you're using things outdoors in any cold zone, stuff made of stone or wood is probably good. :-)