Where do you live? Not zone but location. That info is critical to making any suggestions. Also, how big are the planters?

@gardengal48 (PNW Z8/9)

Of course! I live in southern Ontario, Canada. The planters are approx 18” x 18” x 36”.

Do you have a picture?

Is 36" the height or the length? It sounds as if the soil in these containers could freeze in winter. Does it?

@floral_uk z.8/9 SW UK

Pictured are two dwarf alberta spruce not planted that I’ve realized won’t do well here.

I’m not sure you’ll have much luck leaving them out over the winter in your location, esp if temps go below 10’ F in winter. After a few hard freezes, you could overwinter your containers in an unheated garage, but they would still need to be watered every few weeks until temps get back above freezing and you can put them out again. Or you could dig a hole in your yard and plop your container inside the hole over the winter, mulching good to add extra protection.

If you really want to leave them in place, you could always experiment with trying to add different forms of insulation inside your containers to better protect the roots, but you’re risking having to potentially replace your plants each year with this route.

I've seen dwarf alberta spruce survive in containers locally, but not reliably. Those were part of the decor for sidewalk dining areas, so reasonably sunny all year.

The biggest problem you are going to have with an evergreen is that they require access to liquid water all year. Ice doesn't count. So if the containers freeze solid for enough time, the plants are literally toast. Given the sun and wind in this location, that time may not be very long.

It's a tough ask. Very few plants will tolerate that exposure in winter in a container, as there is considerable risk of root damage from the ambient air temps surrounding the container. They will be far colder than anything the plant would experience in the ground.

So the possibilities are limited. Both dwarf Alberta spruce or Thuja occidentalis (American arborvitae) are potential choices. Of the two, the arbs are somewhat more shade tolerant. And can be found in sculpted or sheared forms for added aesthetic interest.

I complimented my neighbor on her evergreens in planters beside her door. She laughed and said they were fake. They certainly looked very real, even up close.

It is seeming like fake may be a good choice in this case! Thanks all.

Maybe just commission a pair of ornamental metal sculptural supports to grow summer plants on but leave bare over winter. Fake plants are...bizarre. Better to work within your climate's natural limitations and embrace them.

Looking again at your picture, I hope you don't mind me saying that I think the planters would look better placed each side of the doorway rather than each side of the door. At present they are not symmetrical with the entrance. You'd need to get a door mat that went across the whole doorway, rather than just in front of the door itself. You might also need to put something under the right hand one since the decking doesn't appear to extend far enough to support it.