I have done it too. I am not sure, but I would think 7 should work. There is also a forum just for Bulbs, and some of those people probably use containers too, so if you have specific questions, I would post in both fora. I've received good advice there too.

Good, maybe this is worth trying.

It will work (unless they are drowned!). I am in z5, having no problems...Hardy to z3.

I do it all the time, often with several types of bulbs (in same pot)
to get sequential blooming (tulips, hyacinth, daffodils, crocus,
snowdrops ....). Make sure you put your planting together in the fall
and leave it to vernalize somewhere cold but where the bulbs won't
freeze. For me, that's on the garage floor against the interior wall;
then, put them out in spring when new shoots break the soil surface but
bring them under cover if it drops much below freezing. Be sure to use a
very fast-draining soil and toss a little snow on them from time to
time over winter so the soil doesn't dry out completely. Bulbs rot
easily, thus the 'fast' soil, so be careful that you don't over-water
while over-wintering.
You can make extra pots and bring them
indoors after they have time to vernalize (starting early Feb for you if
you keep them cold all fall/early winter). Once they bloom, move them
to a cool spot at night to prolong the bloom life. The procedure
described is called FORCING. (click link)

Well, I'm near Atlanta so it's not too cold here in winter but it does sometimes get down in the teens and 20s at night. I don't have a garage or cold room so if the pots can't stay outside and would be too warm inside, this might not work.

If you leave the pot outdoors and cover it with a box or tub to trap the earth's heat on those really cold nights, you should be fine.

Al

I really don't worry about daffodils in containers, we get many days of -10 *F during the winter. I have some in concrete planter, and many in cheep plastic containers (ones that annuals are sold as 'hanging baskets'). As long as drainage is good and they don't sit in muck, they have np to overwinter.

That's amazing, that's awfully cold.