Posted: 07/10/2014 at 13:22
Hi DD, if they're enormous they're probably N. sylvestris. These are perennial but not that hardy. They do sometimes come through an East Anglian winter but are very late to flower.
From seed is quicker. The seed pods turn brown and the seeds can be tipped out. Make sure they're brown/black and ripe before you collect them. Store cool and dry and sow in very early spring.
I think yours haven't reached seeding yet if they're still green, they hang on to them well and they drop, they don't blow