"O Christmas Tree!
O Christmas Tree!
Thy leaves are so unchanging.
Not only green
When summer’s here
But also when it’s cold and drear."
While evergreens grow all over the world in almost every climate, the trees we think of as Christmas trees seem to thrive in places that have long, cold winters or extremely poor soil.
These trees can survive a short growing season because every spring, they get a head start on the growing season.
While deciduous trees are still waiting for their leaves to open, evergreens are making food and new wood.
It seems like every year, heavy snow and ice damages many of our trees.
But evergreens are adapted to shed snow.
Their green needles are coated with a waxy substance the prevents snow from sticking.
The wax also keeps the needles from drying out.
Occasionally ice crystals in strong winds abrade the wax, and the needles turn brown and ugly.
But winter burn is temporary.
Usually, damaged needles are replaced in spring.
By now, most Christmas trees have been separated from their roots for at least a month, and probably longer.
When a tree is chopped down, it technically is dead.
But death in a tree is not like death in an animal.
When an animal dies, the heart stops beating and blood stops circulating - all body functions cease.
Oddly, a tree continues to function even after it has been severed from its roots.
Water can be absorbed and move through the tree without the aid of a heart.
That means, for a while at least, the needles will stay green even though the tree is dead.
Outdoors, the needles can actually absorb moisture from the air.
But indoor air is dry, so in a house, a tree must have water.
Otherwise, the needles will turn brown and sharp, resembling a porcupine quill or dental probe.
When a tree is cut, sticky sap forms a cap over the wound.
If you let a tree go dry, a cap will form over the trunk and the tree will lose the ability to absorb water.
Without water, even if it is not cold and drear in a house, the green of an evergreen will change.
