Evergreens

This time of year many people use evergreen plants in holiday decorations. How do some trees like the Eastern White Pine stay green in the winter when others like the Eastern Cottonwood do not?


Go outside and look at some of the trees and shrubs which are still green in December. Make drawings of their leaves. Are they thick or thin? Are they broad or narrow? What is their surface like, is it smooth, rough, wax coated, hairy?

Look at the leaves of some house plants. Many house plants are tropical plants which don't usually get exposed to the kind of winter weather we get in the northern United States. Draw some house plant leaves. Are they broad or narrow? What is the surface like, is it smooth, rough, wax coated, hairy?

Think about the needs of a plant. Which can still be met outdoors in the winter? Is there air in winter? Is there soil in winter? Is there light in winter? Is there water in winter? 

 Many trees and shrubs which are evergreen have some way of cutting back on the amount of water they lose from their leaves. The dark color around the edge of this cross section of a pine needle is a layer of wax. How would hairs or a waxy coating keep water from being lost from a leaf? Many evergreens also have chemicals in them which make it harder for them to freeze. 

Try this experiment. Get a saucer and two small cups. Measure the amount of water it takes to fill the saucer. Place the same amount of water in each cup and in the saucer. Cover one cup with foil or plastic wrap, leave the other cup and the saucer uncovered. Put all three containers next to each other. Check them a couple of times a day to see how fast the water evaporates from them. Which one is empty first? Which one is empty last? How are evergreen leaves more like a covered cup than an uncovered saucer?

While evergreen plants stay green all year long, each leaf lives for only a couple of years before it dies and falls off. Look around under an evergreen tree or shrub for old leaves that have died and fallen on the ground. The chemicals in the evergreen's leaves that helped them on the plant can change the soil as they rot. Visit a pine forest and a deciduous tree forest and compare the soils and smaller plants. Are they different?

Would you like to try to identify some evergreens? Click on mystery trees for a fun way to identify plants.

Curious about Christmas trees? Click on Today's Christmas Trees.
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