Unfortunately crocosmias are not hardy to even zone 5. I don't know why they'd even list it to be hardy to zone 5 when it won't survive our winters. It's best treated as you would with dahlias and over winter the corms indoors in peat. Replant in spring.

Crocosmia is very hardy. It survives here, and I have seen it growing on Manitoulin Island.
Some of the leaves on my clump - in the garden for 10 years now, and never winter protected- are also turning brown. I'm assuming it's just summer stress. I'm not worried about it.

Hardiness is dependent on bulb/corm size. The trouble is finding/getting them big enough.

I have to disagree with some of the information here. Most Croscosmia are not hardy in zone 5. You can't even buy most of them in Ontario. The one grown most often is Lucifer and it is the hardiest one.

Does lucifer grow in zone 5? Mine did not come back, and I know several people who can't grow them. However, I also have other friends who seem to have no problems - they grow well and even spread quite quickly.

As to size of bulb, I disagree that large bulbs survive better. I have some seedlings of Licifer that have now survived through 2 winters. My hope is that by using seeds I naturally select for hardy ones. so far so good.

I also have a yellow variety that is not as hardy as lucifer, and it has come back for a second year and last year had poor snow cover here. It is growing wetter than my Lucifer was and it had new mulch so maybe it got luck and had an extra thick mulch layer.

So what is the answer - I don't know. It could be that they need something special in their growing location - maybe more water? It could also be that the source of the bulbs makes a big difference ie the provinence.

My next step is to get some from a garden that has had them for years and try them in my garden.

I also live in Guelph and find that Lucifer usually lives over the winter here. I have tried several other varieties, with mixed success. Some have survived a couple of years and then died during a cold winter. I don't think I will waste my money on any of these ones again. However, I feel that Lucifer is worthwhile, for its unusual bright red colour in mid to late summer. It really adds to a "hot colour" summer garden scheme. If grown too dry it will get spider mites, but is otherwise trouble-free. For me, a "perennial" has to be able to live outdoors 12 months of the year. I don't believe in babying them by digging up the corms in the fall. . . and no,I don't have a greenhouse, either.

I had grown crocosmia in the east end of Toronto. It was planted close to the house, facing south. I had it for several years. When it didn't come up I planted some more without much success. I haven't had any in my garden since. I like them, however, they seem difficult to please.

Crocosmia can become very large clumps here in zone 8 in the Pacific Northwest. I haven't tried many but any I have have been very prolific on the Islands.

no one answered the question at all. Just droned on about how they how they should not be planted in zone 5. That's not what was asked!

I have a potted crocosmia and yes, the spidermites have caused havoc with it, they can easily hide in the groves of the foliage. Most maddening thing was when the plant finally did bloom, it was the wrong variety, had received it via mail order from a reputable nursery.