Tree wrapping is a common preventative measure used to shield young and thin-barked trees from various environmental stressors they face during the dormant season. This practice involves covering the trunk with a protective barrier to mitigate damage from temperature extremes and wildlife. Understanding the precise timing for both installation and removal is just as important as the technique itself.
Understanding Why Trees Need Winter Protection
The primary reason for trunk wrapping is to prevent sunscald, a form of bark injury that occurs during winter when sun exposure is high. Often called “southwest injury,” sunscald typically affects the south or southwest side of the trunk where the winter sun is most intense. On sunny days, the dark bark absorbs solar radiation, warming the inner living cells just beneath the bark and causing them to break dormancy.
When the sun sets or is blocked by clouds, the temperature of the trunk plummets rapidly. This sudden drop causes the temporarily activated cells to freeze, burst, and die, leading to vertical cracks and sunken areas of dead bark. Thin-barked species, such as maple, linden, and crabapple, are particularly susceptible to this damage until their bark thickens with age.
Wrapping also provides a defense against wildlife, specifically rodents like mice, voles, and rabbits that feed on tender bark during winter when other food sources are scarce. These animals can chew a complete ring around the trunk, an action known as girdling, which severs the tree’s nutrient and water transport system and can be fatal. For evergreens, a different kind of protection is needed to combat desiccation or winter burn, which happens when strong winds and sun cause the needles to lose moisture faster than the frozen ground allows the roots to replace it.
Determining the Optimal Time for Installation
The timing for applying tree wrap centers entirely on the tree’s biological state: it must be fully dormant. A common mistake is wrapping too early in the autumn, which can be detrimental to the tree’s health. Wrapping while the tree is still active can trap heat and moisture, creating a perfect habitat for pests, fungi, and bacterial cankers.
The best time to install the wrap is in late fall, after all the leaves have completely dropped, signifying that dormancy has set in. Wait until the ground has frozen or when consistent daytime temperatures remain near or below freezing (approximately 32°F or 0°C). Waiting for these consistent cold temperatures ensures the bark cells are fully hardened and less likely to be prematurely activated. Applying the protection before the onset of the harshest weather and before rodents begin their winter foraging activities offers the most comprehensive defense.
Practical Methods for Wrapping and Spring Removal
Proper application technique maximizes protection while minimizing risk to the trunk. The most effective materials are commercial tree wrap, light-colored paper, or specialized plastic tree guards, which are chosen specifically for their ability to reflect sunlight and maintain a stable bark temperature. It is important to avoid using dark-colored materials, as they absorb heat and can exacerbate the sunscald problem. Non-porous plastic sheeting should also be avoided because it traps moisture and inhibits air circulation.
When wrapping the trunk, start just above the soil line and wind the material upward, overlapping each layer by about one-third as you go. The wrap should extend up to the lowest main branch of the tree to ensure the entire vulnerable trunk is covered. Secure the material at the top with a small piece of tape or twine, being careful not to staple or nail the wrap directly into the tree’s bark.
Removal in spring is just as important as application in the fall. The wrap must be taken off promptly as soon as the danger of the last hard frost has passed and before the tree begins its new growth cycle. Leaving the wrap on too long is hazardous: the expanding trunk can be girdled, inhibiting nutrient flow. Additionally, a lingering wrap creates warm, moist conditions ideal for insect infestation and fungal pathogens. Generally, removal should occur in early to mid-April, depending on the local climate.