Hi brain storm here. Not sure if was mimi or dl but, as promised here is what I found. Maybe other peeps can add refinements!
RHS
Canna
These half hardy to frost tender plants are often lifted to overwinter dry under cover in cooler climates. Divide the rhizomes and start them into growth at 61 deg C for flowers in same season. File or hot water treat the seeds to break seed coat dormancy (so u waz absolutely right). Sow seeds at 70 deg C. Seed raised plants usually flower in second year.
Encyc of Garden Plants and Flowers
What I said yesterday and then treat as any rhizome plant. Can be susceptible to slugs.
Hope this is of some help!
Coo like having gardie again
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