Fall is in full flourish in Howard County, with colorful leaves decorating every lawn. We at Tree Pros say hurray for the one time of year when yellowing, fast-dropping leaves are not a sign of a sick tree (hopefully). What’s with those fall leaves though? Here are our answers to a few common questions.
Why do trees lose their leaves?
During winter, most trees find their best survival strategy is to go dormant, limiting all activity including the circulation of nutrients. Less light means the amount of energy that leaves can produce from sunlight is no longer worth the tree’s investment in maintaining those leaves.
Tiny tubules in the bark that transport water and nutrients to leaves gradually thicken creating a cork-like “abscission layer.” This thickening helps protect branches from cold but it also cuts off nutrients to leaves and eventually pinches off the leaves off entirely.
What about evergreens?
Evergreens take a different strategy and lose needles gradually throughout the year, with about a third of their needles dropping in a year (varying by species).
What triggers loss of leaves in non-evergreen (deciduous) trees?
Longer nights are the primary trigger. Trees actually begin the process of abscission in late June with the solstice, but nutrients are not drastically reduced to leaves until the fall.
Why do leaves change color?
Yellow and orange pigments such as cartenoids and xanthophyll are present in leaves year-round; however, during the spring and summer they are masked by the green chlorophyll the tree produces. Chlorophyll breaks down and disappears faster than cartenoids and xanthophyll, which remain for a time to show their colors after the chlorophyll is gone.
Anthocyanins, the most vibrant red pigments, are produced in some trees when sugars are trapped in leaves during cool fall nights. Adequate sunlight is also needed for anthocyanins to form.
Brown pigments, the tannins, remain the longest. Produced by leaf metabolism, they do not break down in the way the other pigments do.
The timing of changes in leaf color is influenced by a combination of temperature, precipitation, and day length/sun exposure. The best colors come with summer rains, sunny fall days, and cool (but not frosty) fall nights.
Leaf color varies with tree species as well as climate conditions. For instance tulip poplar and redbud trees will have yellow leaves while dogwood and sweet gum will typically have red leaves.
How is climate change affecting leaf color changes?
A study of photographs taken over decades in Acacia National Park, ME, found that peak foliage timing had shifted to a full week later than it was in the 1950s, a change of about a day a decade. Fewer early cool fall nights can mean less red in leaves, less vibrancy to colors in general.
How can I get great fall foliage in my yard?
If you’re planting trees look at species known for good fall display, such as maples, gingko, and many more (contact us or your favorite nursery for recommendations to meet your specific needs and wants). Ideally, plant in a south or west facing area that gets lots of afternoon sun. Lower lying areas can be good in terms of being cooler in the evenings.
For existing trees, the factor you can most easily influence is ensuring that the trees get plenty of water through summer and fall. Verify they’re in good health with a Tree Pros checkup visit.
Will Tree Pros pick up my leaves?
Tree Pros is not able to provide full leaf removal service. We specialize in and have the equipment for larger-scale tree health and safety issues. However, if we are working on your trees we will ensure the area is left neat and clean.
Can I do anything with all these fallen leaves?
Yes, leaves make a great mulch or compost. Set your lawnmower to its highest level; this should allow you to mulch leaves up to 6 inches thick (a mulching mower is even better). Run the lawnmower over the leaves; you may want to go back and forth a few times depending on the thickness of leaves you’re dealing with. Leaves should be broken down to about half-inch pieces, around the size of a dime. If you keep them where they are they will help your lawn (unlike thick leaves that smother), or you can bag them to add them to your garden, flowerbed, or compost pile. (More on mulching)
How can I have fewer leaves to deal with next year?
Pruning your trees reduces branch and leaf fall. While Tree Pros does not generally prune for this purpose alone (we focus on tree health, symmetry, and storm safety), it’s a nice side effect. Please contact us for more information and a free site review and estimate.