I looked around for hardiness advice regarding Eremerus here in Sweden, thinking that the northern parts of Sweden could well be a reasonable match for Canadian conditions. Always difficult to look at the USDA zones and find a good match, because zone by zone the Swedish climate usually is harder on (most) plants. My zone here for instance technically is USDA zone 7b, but that should for actual plant hardiness be more like a zone 5-6 from what I understand, yet of course that depends a lot on local conditions and what the plant is sensitive for during winter.
What I found was that the Eremerus hybrids and E. stenophyllus that I grow are only rated as hardy (according to our Swedish zone system) for the southern parts of the country and along parts of the coast but E. robustus is considered much, much hardier growing well far north. Probably this would be the best species to try for a cold zone. Still growers here in the south sometimes have problem over wintering it. From what I understand this has to do with drainage/winter moisture that can be a real killer.
Eremerus robustus naturally grows on gravelly slopes, so I think a raised bed with lots of gravel would increase hardiness, especially if it could be protected with a raised piece of glass or plastic(with good airflow under it) during autumn rains as to keep the ground a bit dry. When the ground freezes properly one should switch to a dry mulch instead. Of course this is mostly speculation on my part, so take it for what it is, but still these are methods that are fairly common and often can increase hardiness considerably for many perennials.
As a side note E. robustus naturally grows in areas that has real winters, but spring comes fast with no real setbacks, this makes them sensitive to late night frosts after they start to grow. For me E. robustus is a very new plant, but I already find it interesting comparing how it grows with the older Eremerus (well they are only a few years old) in my garden. So far the growth point seems to expand a lot more during the winter than the rest of them. This makes me believe that it may well need more protection from late frosts than the others I grow.
