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10 FALL 2015 ARBOR AGE www.arborage.com PLANT HEALTH CARE degrees Fahrenheit where I live) and, remarkably, the trees survive all season just fine. However, if one were to move a cold-hardy tree, such as a paper birch, into a -20-degree Fahrenheit freezer in midsummer, the tree would be dead by morning. Just like you need a wardrobe change before going from the beach to a snow bank, trees need to get prepared for cold temps by "hardening off " before the cold sets in. The liquids within the cells of the tree, known as protoplasm, change their concentration of sugars and salts — essentially lowering their freezing point, and allowing them to withstand frigid temps. Different plants have differing abilities to do this, which is what gives rise to the USDA hardiness zone map. The seed source plays a role in hardiness as well for trees with a wide geographic range. Red maples (Acer rubrum) are native from Florida to Ontario, but transplanting one from the South to the North or vice versa would likely be its demise as there are adaptations they have made over time to thrive in their native conditions. During the winter, trees are dormant, but that doesn't mean lifeless. Quiescence is a term that roughly means "resting but ready," and that's what trees are doing during winter. There are metabolic processes going on even in extremely low temperatures. Evergreens continue to respire, moving liquid water from the soil up through their stomata in the leaves. Winter burn is a common aliment on conifers as the sun heats up foliage, causing desiccation (if no liquid water is available, the foliage dries out and dies). Winter burn is most common in years of low snowfall, as the snow acts as an insulator, preventing the soil from freezing solid too deep. Below ground, the soils are often warmer than the air, and roots have adapted for this. In fact, the air can be 20 degrees Fahrenheit and the soil can be as warm as 35 degrees Fahrenheit. Utilizing stored energy, trees can send roots out to explore for resources and grow in the spring while the world still looks to be frozen. Caring for trees going into winter can be done with some simple tips for tree owners. Continue to water trees, particularly evergreens, weekly until the ground freezes. Trees are often fertilized in fall. This puts the nutrients where they are needed for spring; and nutrients such as potassium can benefit evergreens throughout the winter by reducing winter burn. Many plant health care treatments, such as soil applications of insecticides or applications of injectable nutrients such as iron and manganese are also applied during this season. Protecting trees from rodent feeding during winter can be achieved by wrapping trunks of young trees with corrugated plastic tubing. Wrapping evergreen foliage, or even creating a screen with a fabric such as burlap, can prevent winter burning and reducing the browsing of hungry deer. Winter may be hard on humans, but our trees are pretty tough. Given the proper care through the growing season and into fall can put them in a position to thrive when spring arrives again. This is true for young tree, mature trees, and even little trees in pots. Brandon M. Gallagher Watson is creative director at Rainbow Treecare Scientific Advancements, and is an ISA Certified Arborist (#MN-4086A). PHOTOS COURTESY OF RAINBOW TREECARE SCIENTIFIC ADVANCEMENTS Winter burn often occurs on sunny side of the tree. Conifers, such as white pines, shed 3- to 5-year-old foliage each fall. Protecting evergreens from the sun can help prevent winter burn.