A number of conditions may cause WINTER BURN on both coniferous and broadleaf evergreens.
Winter burn may also be found on dormant foliage and flower buds on deciduous woody ornamentals.
1) When the sun is too intense and the leaves give up their moisture, this typically results in browned foliage being manifested on the southern facing sides of the plant. If the winter burn is minor, only the upper-surface of the foliage may be burned. Gently turn over the leaves or branch and note the color on the bottom side of the leaves. The bottom surface should not be browned. However, if it is, then the winter burn is severe. You may also notice that leaves being shaded by other leaves have less winter burn or even patterns resulting from the shade.
2) During the Winter, if the leaves get too warm, thaw, and then freeze almost instantly, the foliage and often the buds also turn brown. This is common near a clothes drier, furnace or hot water heater vents. Prolong exposure from engine exhaust, such as cars and snow blowers can cause the same winter burn.
3) Winter burn is also found on plants located where they warm up above freezing long enough for the foliage to thaw -- then followed by rapid freezing of the foliage. This may occur in the protected alcoves of buildings or other structures, particularly if the buildings are darker colored and prone to solar heating. The more often this occurs the more severe the winter burn damage.
4) Dog or other animal damage due to regular urination on or at the base of plant often causes browning of the foliage, even during the growing season.
5) Salts, such as deicing salt on the foliage or near the roots cause desiccation of the foliage or modify the plant’s ability to maintain proper hydration.
6) Insect and mite damage can weaken the foliage and predispose the foliage to winter burning.
7) Rodent damage -- chewing on and damaging the trunks and stems can affect small twigs or even entire branches and trees. This is very common on lower conifers, such as Juniperus-Juniper. Rodents enjoy the comfy crown – roof – of the low growing junipers and dine on the nice tender bark in the immediate vicinity.
8) Some species and or cultivars of plants from southern provenances are more prone to winter burn than others. Even though plants may be found over a wide range of ecosystems, those from northern provenance are typically better suited to survive our Midwestern conditions. Plants grown in southern California and other southern states and shipped to the Midwest have never experienced our weather.
Plants raised in the Midwest have gone through a number of Winters – with the strongest surviving and hopefully being available in our local nurseries. Some taxa are tolerate of our winter temperatures but cannot tolerate solar desiccation. Hardiness zone ratings, which only look at temperatures, do not take into account provenance and a host of many other factors contributing to a plant’s hardiness.
9) Plants coming into a flush of growth too late in the season, not allowing for the foliage to mature and 'harden off' before winter, often have browning and dying of that late season growth. Just prune it out.
10) Chemical damage including herbicides accidentally being applied on or near the plant can cause burning. Mismanagement or poor timing of chemical applications can outright burn the foliage or sensitize a plant to the vagaries of the weather, resulting in winter burn.
11) Physical damage from children, pets, animals, heavy snow, ice, etc., breaks leaves, stems and even entire trees. Minor damage would need to be assessed to learn if the integrity of the plant has compromised, or if the entire limb or tree needs to be removed.
12) Nutrient or pH imbalance may also be a causal agent for winter burning. If a leaf or twig growth has been compromised due to an imbalance of nutrients, the additional stress caused by winter weather, droughts, insect damage, etc., may result in browning of the foliage. These imbalances often manifest themselves during the previous growing season. Action should be taken to correct these imbalances as soon as possible. What to do for winter burn Typically, even if the foliage browns, the dormant buds may be okay. However, sometimes the main terminal buds are also damaged, but the lateral-side buds are fine. New growth would come from the lateral buds. This happened a number of years ago on maples, oaks and numerous other woody plants where the terminal buds died but the secondary, dormant and or lateral buds pushed nice growth, resulting in good seasonal foliage. Most people didn’t even notice their woody ornamentals had suffered the loss. Do NOT prune until AFTER Spring growth has actively begun. This allows you to determine if any pruning or other measures may be required. Water as soon as the earth thaws and drying conditions are manifested. If lack of nutrients is suspected, fertilize very lightly once active growth has begun. Then, in mid Autumn fertilize with normal concentrations. Maintain healthy growing conditions for the ENTIRE following season.
originally published in Newsletter Vol 27 #1