Hi Carmen and welcome! The same seemed to have happened to my itea (it did okay last winter but obviously this winter, the warm early part and freezes in March/April seems to have done it in). Similar happened with my clethra (it was also a "Hummingbird", athough it was a small cutting size and I didn't want to keep it inside but probably should have). So those 2 are iffy and outside of requiring alot of water as their preference, they seem to be a bit tricky in pots without some protection for them in winter in the colder zones.

A good rule of thumb is to look for plants 1 - 2 zones hardier than where you are if you want to keep them outside in pots with little or no protection. So in that case, the aronia (as a zone 3) and the hemlock (as a zone 4) should be okay. This is also assuming that you can get them through that first winter and once they are established, the zone 2, 3, & 4s are pretty carefree.

Provided that you right-size the pot for them and give them fertilizer and water (and keep them away from windy spots), they should do fine.

Just as a follow-up, I was out watering this morning and although all of the top of my little itea died back convincing me that it was a goner, one small section near the base that had remained strongly green has just sprouted this week (this little guy was originally from a free cutting that I picked up at a garden fair a couple years ago so it had been a small plant). So it is alive and I'll cut back the top and let it grow out again. It did the same thing last year but not to this degree. The nice thing about the itea (and I am thinking that mine is the dwarfish "Little Henry" because it hasn't grown as quickly as other shrubs that I have) is the beautiful fall coloration on the leaves and persistence of the leaves late into fall and early winter.