Water them before it gets polar cold. That will slow the soil from freezing and help keep them hydrated if a big wind comes with the cold. New tender growth will freeze. Old growth not so much. It wouldn't hurt to cover them just for some extra protection.

Are the containers too heavy to be moved to a sheltered location for a while? That worked for me in Zone 6. I would drag them under a shrub, or behind the house. It was always the wind that did the most damage, desiccating the newest growth. The lowest temps I remember were just below 0F.

I also had a bunch of burlap bags that I made to throw over the plants. They were deep enough to cover the plants and the container. This way I didn't have to worry about them flying away. You could also use large cardboard boxes, with some kind of weight on top. The idea is just to create a windbreak, not control the temperature.

Whatever you, don't use plastic.

It is not the top growth that I would be worried about, although I would try to avoid wind desiccation. With any containerized plant, it is the root system that is at greatest risk from cold damage. Roots are the most cold sensitive portion of any plant and in a container, without the insulating mass of all that ground soil around them, they can be exposed to very cold ambient air temps......much colder than any frozen ground soil.

0F is very cold for a zone 8! That is dropping down in zone 6 territory! Very few roots will survive exposure to temperatures that low for long. As Christopher noted, make sure the containers are watered well before the cold hits. And protect the containers as best you can - wrap in bubble wrap or burlap, pile up a thick mulch around them or buffer them with hay or straw bales. If that is impractical, then I would strongly urge moving them into a more protected location.

probably depends on the duration of the cold .. and the size of the pots.. as to how cold the roots might get...

big city name will help ... also size of pot..... and plant...

perhaps a pic or two would help us... help you ...

if the pots are so big.. you cant drag them into the garage or some such ... then it would have to be a pretty long cold snap to freeze a pot ...

im not sure i would heavily water a pot with cold tap water.. and start the whole process by chilling the media ... are your pots really that dry that this is imperative??? [and i surely wouldnt use warm water .... and dont call me Shirley ... ]

what is the wind forecast during this period???

ken

btw ... i dont understand this part?

==>> but ~85% of each plant is established.

ken, if the temps drop as low as 0F, it won't take long for a container full of potting media to freeze solid. Depending on size, it could happen as quickly as overnight.

btw, if you think cold tap water is going to overchill roots in an outdoor container at this time of year, well then.........I'm not sure what else there is to say !! L0L!

The variables in spring freeze damage are too numerous to count. One thing is certain, potted plants are more susceptible to damage. A dramatic swing and polar vortex blast like this is even worse. The more that can be done to protect the potted boxwood the less chance of damage.

But weathers depending, 0 degrees in zone 8 in mid February has the potential for damage to landscapes far beyond the pots in question. Like kiss your camellia flowers goodbye.

Good point, Christopher! I remember a polar vortex event in Maryland (around 0F) that killed all in-ground rosemary plants in the area, as well as Spanish lavender, camellias, verbena, etc.

This event was preceded by a few warm winters, and the nurseries in the area started aggressively promoting Zone 8 plants. My neighbors even planted a banana... Needless to say, the damage was substantial.

Thank you all for the recommendations! I had kept up with a 1-2 times a week watering schedule until December, where afterwards I reduced watering. I noticed new growth the past few weeks which was a bit surprising for winter. They had been doing okay with 20 degree weather the past few days, but we covered them last night as the temperature will continue to drop and we want to protect them from the wind.