Desconhecido, mas talvez porque seja incomum
Como indicado no comentário de Richard, a idéia do aipo se deve ao produtor, John Nathan-Turner, que fez não oferecer uma explicação para isso .
The celery was John’s idea. He just came to me one day and said ‘I think the new Doctor should wear a stick of celery on his lapel’, and so that was it. Funny, really, because I don’t much like celery and I usually ended up getting presented with tons of the stuff at conventions! It was nice that it was actually explained before I left the series."
—Peter Davison
Davison mais tarde ampliou isso :
At the first costume fitting, [Producer] John Nathan-Turner said I should have something odd and unique on the lapel. And he came to me a couple weeks later and said, ‘stick a celery on your lapel.’ I said okay, as long as you explain it. And we preceded to do three seasons and I said, you still haven’t explained the celery. So they wrote this bit for my last story ‘The Caves of Androzani’ that explained it as an antidote to a poison... which it also detected.
Assim, parece que a principal razão para escolher o aipo foi que era incomum.
Note que isso mostra que as justificativas no universo são claramente não razão original de Nathan-Turner , uma vez que Davison teve que pressionar para que tal explicação fosse dada.
Ele também deu uma explicação faceta a certa altura, embora seus comentários posteriores (e o fato de que Davison não gostava de aipo) sugiram que isso não deveria ser considerado verdadeiro:
“In case I get peckish!” said Peter Davison. We were in the Tardis. Not the real one I grant you, but a mock-up at the Longleat Doctor Who Exhibition way back in 1982. The snotty-nosed eleven year old incarnation of myself had just asked his beloved fifth Doctor why he always wore a stick of celery on his lapel, while he scribbled his signature on my Doctor Who Annual. It was an entirely valid question of course and the Doctor had given me a completely honest answer. Or so I thought.
Como sugerido pelo Tardis Data Core , é possível (embora talvez não seja provável) que Nathan-Turner tenha sido inspirado por Os Vingadores (a série de espiões de 1960, não o filme de super-herói), onde a noção de um personagem vestindo aipo já havia sido mencionada anteriormente.