- Leaves of some trees such as birches, tulip poplars, redbud and hickory, are always yellow in the fall, never red.
- Leaves of evergreen trees stay green all year but drop some their older leaves, or needles, which can turn bright yellow, in
spring. Evergreens never drop all their leaves at one time.
- The shortening of the length of day is the primary event that triggers the changing of colors in leaves Moisture and temperature also are a factor. play a role. A dry summer can delay the changing of the colors in fall.