In message , Janet Tweedy
writes
I wanted to try "Ne plus ultra" and Alderman this year. Both very old
varieties.
How far apart would I need to grow them to ensure that if I saved the
seed for next year it wouldn't be a 'mix'?
Or is it not possible at all?

Janet

Peas (Pisum sativum) routinely self-fertilise, so the expectation would
be that the majority of saved seed would come true. Hpwever I can't tell
you to what degree cross-fertilisation also occurs.
--
Stewart Robert Hinsley