Tree Talk: Falling Needles and Leaves

 Many people pick fall as their favorite season of the year.

 We welcome the cooler temperatures, the occasional much-needed rain with a little thunder mixed in, and the cheers of football season!

 Fall colors exhibited by deciduous trees and shrubs are a product of shorter days. Summer sunlight triggers leaves to keep making chlorophyll, necessary for photosynthesis and the whole sugar-making process, enabling a tree to grow. But as the hours of daylight become increasingly fewer, leaves recognize the signal to prepare for winter and to stop producing chlorophyll. Once this happens, the green color starts to fade and the red, orange and yellow pigments become visible. These “fall colors” were in the leaves all along – but they were masked by the intensity of the growing-season chlorophyll.

 There’s lots of chemistry going on inside these woody plants. Fall color is intensified and is most vibrant when fall days are cool and sunny, and there has been adequate moisture during the growing season.

 Most trees across North Dakota’s landscape will produce yellow to brown fall color. We can see orange to red coloration with a few trees including Ohio buckeye and Amur maple. Shrubs that show off their

fall leaf colors include euonymus, cranberry bush and nannyberry viburnums, and sumac.

 At least we have evergreens (conifers) to provide year-round color! Pines have long needles which are held onto the stem in clusters called fascicles. Scotch pine trees have two needles per fascicle, about 2 to 4 inches long. Older scotch pine trees will develop an orange-looking bark. Ponderosa pines have much longer needles, 4 to 9 inches long, in bundles of two or three. Pine needles live for 2 to 7 years, then die and drop during the fall. These are the older needles towards the center of the tree and this is normal needle-drop.

 Spruce is the most commonly planted conifer in North Dakota and is an important component of landscapes and rural windbreaks. Spruce needles are short, about ¾ to 1 inch long and are attached to the stem individually. Colorado blue spruce (most are actually more green than blue) needles are sharper than Black Hills spruce. Spruce needles usually live longer than those of pines and may persist for up to 10 years. Like pines, spruce needles near the center of the tree which are older and more shaded will turn brown and drop in the fall.

 We may be startled to notice needles that turn brown and drop to the ground, but this is normal – as long as it is the older needles near the center of the tree. If all the needles on a branch are browning, there are other problems. Drought conditions can lead to decline and death, but too much moisture is not suitable for conifers, either. Sometimes it’s the soil that is not a good fit for certain trees. North Dakota is a prairie state and trees have simply been planted where we want them or feel we need them but where they would not naturally occur. Thankfully, most trees are tough and with some care, they provide beauty and benefits for years. Enjoy the fall colors!