You may be very proud of the fact that the orange tree in your garden only comes up to your shoulders, but that is just one part of the tree that you see. Sometimes a tree’s roots, beneath the soil, are much bigger than the parts you see above the ground. It is with these roots a tree looks for water that gives it life, and makes its leaves look shiny, bright and healthy. In fact the leaves need to take in a lot of water to stay that way.
Now you know the reason why trees shed their leaves in winter. The reason is simple: in winter, the soil gets cold and hard. And it is very, very difficult for a tree’s roots to find enough water in that frozen soil. So the tree makes a plan for these hard winter months; it sheds its leaves in autumn so that there are fewer leaves in winter. The fewer the leaves, the more is water saved in the cold winter months.
You may now ask how the tree knows when to shed its leaves. The answer is simple: with the passing of summer and the onset of autumn, the days become shorter. The air, too, gets cooler. As winter sets in there is cooler weather and much more darkness. And that is the signal the tree is looking for; it knows that the time has come to shed most of its leaves.
As soon as the tree catches the signal that it is time to shed leaves, it puts a fantastic plan into action. It cuts off the water supply of the leaf. It does this by sealing off the leaf stem from the branch. When the leaves do not get water to make their food they start dying. Their shiny, green colour changes to a dry yellow, red and brown. Finally the leaves fall.
And when winter passes to make way for spring, the soil opens up and the root finds it easier to search for water, and to have more leaves. That is when trees start getting fresh leaves.