Since ancient times people have been adorning their homes with holly, evergreen trees and ivy in December.  During the cold dark days of winter, much of the landscape is dreary, but certain varieties of plant life remain green year round.  Some also produce bright red berries bringing a bit of cheerful color to an otherwise bleak landscape.  In order to get a sense of happiness and a hope for the future joys of spring, people began to bring in these evergreens into their homes. So how do evergreens stay green? Evergreen shrubs such as holly face many challenges during winter. Actually, cold temperatures are the least of the plant’s problems. Photosynthesis can occur in many plants when temperatures are at or a few degrees below freezing. The biggest problem for plants in winter is drying out. When the ground freezes, plant roots are unable to draw liquid water from the soil. Then the plant becomes dehydrated, and the plant cell membranes lose their shape and rupture, killing portions of the plant. Cell tissues can also die if ice crystals form inside cell membranes. In order to combat drying out, holly plants, evergreens and certain ivy have tough leathery leaves that are resistant to drying out. The thick waxy covering of the leaves allows the plant to live through the winter. Also, evergreen trees have needle-like leaves instead of broad flat leaves.  This shape helps conserve any water that remained from the warmer weather.