How do plants detect seasonal changes?

through their leaves

they respond by loosin their leaves in the fall and winter and growing them back in spring . this happens by plants stop p making chloroplast when they feel like its getting cold. by not making chloroplast [it makes the leaf green it makes the leaf turn a yellow,orange,or brown colour .when they feel winter is over and spring is comming they start to grow leaves again by by making chloroplast once again.and the process stars all over again.