vio wrote:
Gardening in Toronto and have Crown Imperial Fritillarias -- they come
up every spring, seem green and thriving, then gradually yellow and die
back. After two years, they have never flowered. I've dug them up and
the bulbs look solid and healthy. Any suggestions deeply appreciated.



I googled "fritillaria", and found:
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These large, exotic bulbs are perfectly hardy but might take a year or
so to settle down. Plant them hollow side up in full sun or light shade
in fertile, deeply dug soil. They seem to prefer a somewhat heavy soil,
in sandy soils work in some compost or leafmold before planting.

They make good border plants and are particularly effective in front of
a stone wall in groups of 6 or more.

Fritillarias are heavy feeders and benefit from a mulch of decayed
manure or leafmold in the fall and a dusting of bulb food in early spring.

Plant 6 inches deep, 10 inches apart.
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Your answer is probably in there.