April/May, sometimes into June - most are biennial.

Thank you

Remember that if you planted it this year it will not flower until next year. Thereafter it will flower only for a few years more and then that's it.

Ours have just opened. If you cut the main spike below the last bell after its finished you should get a lot of smaller ones from lower down the stem. They are not as tidy or impressive but they do extend the flowering period.