Crocosmia are rated to Zone 5 so theoretically could stay in ground for the winter. I'd be inclined to plant them fairly deep then mulch for winter of 3-4" of straw, bagged leaves or similar just to be assured the bulbs don't freeze. Alternatively you could plant them in pots ( larger than the nursery pot you purchased them in) then lift the pot(s) in late fall and overwinter indoors in a cool location. You would need to keep them slightly moist but not wet until spring so the bulbs don't dry up.

Mobot (Missouri Botanical Gardens) basically says the same thing and they are in a similar zone to yours. If you google Crocosmia Lucifer you will find lots of info.

Mine stay inground year round but our coldest winter temps thus far have been -12 or so, thus a little warmer than you may experience.

HTH
Holly

Here is a link that might be useful: Mobot

I have planted different crocosmias 2 different times here in zone 5b/6a, and have never had them survive the first winter. I didn't however plant them extra deep or mulch them much other than maybe an inch of shredded bark mulch

Sue...chemocurl

My Lucifers lasted 2 seasons. They showed some increase in season two which surprised and pleased me. Unfortunately nothing returned in season three. Very disappointing.

Hmmm..sounds like this may not be a long term plant in this neck of the woods. Our winters can go in the -30C + here. They are planted directly in the ground now but I think I may dig them up in Sept or so. They really are quite lovely and I would like to try and keep them. If they survive in the house I will be putting them in a larger pot next year.
Thanks so much for the info.

You can probably leave them in the ground year-round in Can.zone 5b. That is the same zone I am in. (Guelph, Southern Ontario) I have had Lucifer for over 5 years in the ground here. For some reason, some of my plants (i.e.corms) died last winter, some, but not all of them. Since you are planting them in mid-summer, rather than in the spring, I would advise lifting them this winter. However, to save extra work, I would leave them in the ground in future years. Lucifer are relatively easy to obtain and not expensive, so it is worth taking a a chance on them. At least, that's my opinion, and what I intend to do. I will buy a few more corms next spring to replace those of mine that died last winter.