Fall is a great time of the year. The trees start turning colors and everything looks so beautiful, even the green conifer trees. Evergreen trees should maintain their green color all of the time, right? This time of the year I get many calls on a natural process of evergreen trees called Natural Needle Drop.
Natural Needle Drop
Evergreen trees turning yellow in the fall may not be a problem, in fact it may be completely natural. Evergreen trees do hold onto their needles, but eventually the older needles are shed from the tree in the fall. When this happens, those needles turn yellow before they fall from the tree. As long as the needles that turn yellow are all on the interior of the tree, there is no real concern. The older needles are the needles that are shed, which will be held on the interior of the tree, not on the ends of the branches.
Natural needle drop is very noticeable on white pine trees because they are naturally not a dense tree and they lose their needles every 2 years, making it quite common. Ponderosa pines lose their needles every 3 years, while Austrian pines lose their needles every 4 years. It is not as common to notice the needle drop on these trees due to the infrequency as well as the density of the tree. Spruce trees will also lose their needles, but much less often. Spruce trees will typically hold onto the majority of their needles for up to 10 years
It is important to know what you tree is supposed to do in the fall and winter months. We have a couple of trees that are classified as ‘Deciduous Conifers’ meaning that they are a conifer due to their needles and how they are arranged but are deciduous because they lose those needles annually. Two deciduous conifers are commonly found in Nebraska, the Larch and Baldcypress. These trees will lose all of their needles in the fall after first turning brown throughout the entire tree. If you don’t know what type of tree you have in your yard or are not familiar with the growth habit of these trees, you might think they died, when they are really just going through their normal lifecycle.
Fall Color for Deciduous Trees
Speaking of deciduous trees, this is the time of the year when our deciduous trees, those with leaves rather than needles, will change color and the leaves will fall from the tree. As the nights gets cooler and the days get shorter, the tree produces a membrane between the branches and the leaves which causes the leaves to be shed from the tree. Prior to leaf drop, this membrane also causes cessation of chlorophyll from the leaves for the year. At this time, the other pigments are allowed to show up in the leaves.
The brightest fall colors are produced when dry, sunny days are followed by cool, dry nights. The dry, sunny days are needed to break-down the chlorophyll in the leaves allowing the other pigments to be dominant in the leaves. The cool, dry nights are also necessary for fall color because trees need to avoid freezing temperatures which can injure or kill the leaves causing them to stop producing much sugar at all. The sugar content is what increases the amount of the anthocyanin, or red pigment.