How do plants know when it is spring time or winter time?
Plants respond to long term changes, yes two equinoxes are indistinguishable in terms of light levels on the days themselves but the surrounding days both before and after are mirror images of each other.
This longer term change in light levels is how plants regulate their seasonal behaviour.
Thanks ryan_m_b. Can you point me to some reading/reference materials on this particular subject?
I'm afraid I don't, I'm not a plant biologist and it has been years since I have studied the topic. I'm sure there are some books that you could find on plant biology written for the layman, perhaps Botany for dummies? I haven't read it but I have found the "for dummies" series to be very good at producing explanations for a non-expert.
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