How do trees know when to let go of their leaves and when to regrow them?

Question

How do trees know when to let go of their leaves and when to regrow them?

In: Biology

Answer 1

Temperature and daylight hours, mostly. Plants have hormones, and the hormone balance changes with changing environmental conditions, making the trees transition to the next phase.

Fun fact: many fruit trees in temperate climates need a certain number of chill hours, which is time spent above freezing but below +8°C, or they won’t flower and set fruits properly the next year.