Well, most plants, if not all, are temperature-scopic. OK, made that word up but they sense temperature and get triggered to start growing when to the T goes above a certain level. Night-time Ts are important here too. Trigger timing varies between species of course.
Last year my plum tree didn't give any fruit at all due to a late cold period in early springtime. Have better hope for it to give some fruit this year. (bet it does)