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from "La Puce" contains these words:

On 28 Feb, 17:45, Janet Galpin wrote:
I start Peer Gynt or any other early sprout in about the second week of
March and late sprouts in early April. I'm in South Lincs; in Manchester
you might need to go a week or so later.

I had indeed thought to do this around the new moon (19th March). I
didn't know there was 'late sprouts' too. Thanks Janet.

Yes, Peer Gynt is particularly early and can be ready from about
September onwards. In seed catalogues it usually tells you when a
specific variety will be ready. By growing about three varieties you can
have brussel sprouts from at least September to March. Some I've tried
are Peer Gynt and Oliver - ready August/Sept to November; Diablo - ready
Oct - January; Wellington and Braveheart - ready January - March. Times
are only approximate; they will overlap and depend upon planting times
etc. but should give some idea.
Janet G