Justin Evertson, Nebraska Statewide Arboretum
Although most conifer trees are considered to be evergreens, all of their needles eventually fall just like deciduous trees. What makes them evergreen is that their leaves/needles persist more than one year before falling. Since new needles are added every year, there is always an overlap between green needles and those that are due to fall.
Most pine trees retain their needles for three to four years before dropping. Depending on the species however, the period of retention can range anywhere from two years for some faster-growing types to more than 15 years for slower-growers like bristlecone pine. In the Midwest, the evergreen with the most prominent needle drop is white pine. Every fall these trees appear sprinkled with yellow, desiccating needles. People who experience this for the first time often assume these trees are sick or dying.
Needle drop is least evident on junipers, spruce and fir trees. On these species, the needles typically persist until they are shaded out by branch growth. Since these needles don’t dramatically change color when they drop, the act of shedding usually goes unnoticed. However, walking under a mature spruce tree barefoot would painfully reveal the truth about needle drop.
Believe it or not, some conifers shed all their needles every year. These deciduous conifers include larch and bald cypress. The larch with its golden yellow and the bald cypress with its bronze hues can add great beauty to the fall landscape. Such trees are unusual enough that more than one story has been told about these trees being cut down after they were mistakenly determined to be dead. So enjoy the fall color and know your trees before cutting them down!