Did You Know? Proper Tree Pruning Can Prevent Storm Damage

Winter can be hard on everyone, and that includes your trees. Winter temperatures that fluctuate during the day and overnight can stress dormant trees in several ways, with one of the most common being frost cracks. Ever thought you’ve heard a sharp rifle shot out of nowhere from a snowy forest, woodland, or your own garden? It could be a frost crack announcing itself. While we can bundle up in extra layers when temperatures drop or remove those layers as it warms up, trees don’t have any outerwear beyond their bark to protect themselves from fluctuating winter temperatures. And when those temperatures rise or fall suddenly, frost cracking often results. In This Article … In this article, we answer some of the most-asked questions about frost cracks in trees, including: What a frost crack is and what it looks like What causes tree bark to split in winter When trees are more likely to get frost cracks Why it makes such a loud noise when a tree cracks If frost cracking can kill or damage a tree and what you should (and should not) do about it How to prevent your trees from cracking in freezing weather, and where to avoid planting new trees Which trees are most likely to get frost cracks And more! What are frost cracks? Frost cracks are vertical cracks in a tree’s bark and wood that appear on its trunk or branches in winter. While humans aren’t built the same way as trees, we both have internal systems full of water that are covered by a protective layer. In winter, we’re protected by extra layers and heated buildings, but trees endure sudden and extended periods of temperature changes outdoors. Sometimes these temperature changes are greater than a tree’s structure can endure. The result of winter weather changes can cause frost cracking. What causes frost cracks in trees? Frost cracking is caused by the tree’s inability to endure the expansion and contraction of its bark and wood that results from the expansion of water inside its wood. Ever put a bottle or can in the freezer and forgotten about it? You might find it cracked open, in a pool of frozen wine or soda. Water responds to temperature changes by expanding. While cooling water initially contracts, freezing water expands by as much as 10%. Note that warming water also expands! Because water expands when it freezes, it takes up more space. Rigid “containers,” such as a tree’s bark and the wood just beneath the bark, can’t always flex enough to accommodate the expanding water. The result? Cracks in the tree as the water molecules inside the tree’s cells expand. When do frost cracks happen? Frost cracks are most likely to occur when there are larger fluctuations between daytime and night-time temperatures. In winter, sunny days with warm temperatures heat up the tree’s bark and its internal layers near the bark’s surface, causing them to expand. The warmer the temperatures get and the longer the warming lasts, the deeper the warming will extend into the tree’s tissues and the more the bark and wood will expand. When those warm daytime temperatures plunge in the afternoon and freeze overnight, the surface bark cools quickly and contracts. However, wood that is deeper inside the tree cools and contracts more slowly. As a result, the more rapidly contracting surface bark is stretched taut over the still-expanded inner wood. After a certain point, the shrinking bark (and, often, the wood layers immediately beneath it) can no longer hold together, and it cracks. Where do frost cracks usually appear? You’ll most often find bark cracks on the south and west sides of a tree. This is because these sides receive the most hours of warming sunlight before night-time temperatures drop. Why do frost cracks make such a loud noise? The rifle shot sound that frost cracks make is the sudden snapping of wood that has reached its limit of flexibility. It’s sudden because until that moment the tree has maintained its tensile strength. As soon as the forces of expansion and contraction exceed the wood’s strength, the wood fails all at once. Freezing temperatures usually reduce outside activity and noise, snowfall muffles sound, and cold, still air carries sound well. Together, these factors help amplify the sudden sound of wood cracking. A large frost crack that has grown wider over the years due to fluctuating temperatures Frost cracks on trees can grow wider if they are damaged every year. Do frost cracks close up on their own? The wounds from frost cracks may never fully seal up and may reopen during subsequent winter temperature fluctuations. However, healthier trees are better able to seal off (compartmentalize) the vulnerable or diseased area to safeguard the rest of the tree’s internal system. Trees also respond to frost crack damage by creating “reaction wood.” This new growth around the damaged area can help seal it up. Reaction wood is stimulated to grow after dormancy ends when all parts of the tree have woken up and are growing again. If reaction wood is successful, the wound will be buried within new growth layers and be less likely to crack again during freezing winter weather. Can you repair a frost crack? Trees have built-in methods to control and isolate areas of disease or decay. The best way to deal with frost cracking is to let your tree do its work. Don’t use a sealant or patch to cover the crack. Just like sealing the surface of pruning cuts, this is an old habit that has been proven detrimental to tree health. Can frost cracks kill a tree? Maybe, although it’s not the frost crack itself that kills a tree. A tree’s bark is its protection. When that protective bark is breached by frost cracking, the tree’s internal wood is left vulnerable to attack. The open wound allows insect pests and diseases to get a foothold inside the tree, potentially killing it. Can you prevent trees from cracking in winter? You can’t control the weather, and you can’t bring your trees inside for some cocoa, but you can help them endure the worst winter weather and resist frost cracks. Follow these tips to help prevent trees from cracking in winter: Ensure your trees are as healthy and vigorous as possible Irrigate your trees during dry winter periods (well-hydrated trees are less susceptible to all sorts of damage, including freezing) Add compost to your soil in spring and/or fall Spread a 2-4” layer of organic mulch around the tree’s dripline in the fall to help minimize temperature fluctuations in the soil during winter’s freeze/thaw cycles Provide organic and slow-release fertilizers for the growing season Wrap trunks with burlap in winter, when it’s feasible to do so Don’t prune your tree if you don’t know how to do it correctly—hire a professional! PRO TIP: Wrapping tree trunks with burlap provides some protection from temperature extremes and also helps prevent winter sunscald on young trees. Just remember to remove the wrap as soon as temperatures rise and the risk of freezing weather has passed. If you leave it on too long, it’ll trap moisture against the tree’s bark, and you don’t want to provide a place for overwintering insect larvae to hatch. And don’t suddenly change the environment around an existing tree by clearing away all plants, shrubs, and adjacent trees (for example, during construction or major landscaping project). Doing so will expose the tree’s trunk and branches to unbuffered winter weather. You can shock your tree with the stress of this change and make it more susceptible to insects and disease, in addition to frost cracking and sunscald. Wrapping burlap around young trees can protect the thin bark from frost cracks. Which trees are more likely to get frost cracks? Many common tree species are susceptible to developing frost cracks in winter, especially those with thin bark. You’re more likely to find vertical splits from frost cracks on: Beech Linden Maple Oak Sycamore Walnut Willow We’re not suggesting that you shouldn’t plant these trees; they’re excellent choices for many landscapes. But do remember to check them (and all your trees) regularly for frost crack damage in winter. Keep your trees vigorous and irrigated, and you’ll lessen the severity of frost crack damage. PRO TIP: Young trees with thin bark are often most susceptible to bark cracks in winter. They are also more susceptible to winter sunscald, which shouldn’t be confused with frost cracking. Sunscald can also damage or kill inner bark, but this damage won’t show up until after dormancy has ended and the young tree resumes growing. The dead or damaged areas will not grow and will appear sunken or discolored as the surrounding areas of healthy bark continue to grow. Does location affect whether or not a tree will split in winter? While you can’t move established trees to a more winter-friendly location (at least not easily!), you can choose where to plant a new tree. If you’re planting a new tree, especially one that’s more susceptible to frost cracking, locate it in an area with good growing conditions and where it will be protected from extreme temperature swings. Follow good planting practices and avoid planting your new trees in areas that: Are fully exposed to strong winter winds Have shallow or infertile soil Have overly fast-draining soil Think Your Trees Have Frost Crack Damage? If you think your trees have sustained damage from frost cracks, give us a call. Often, your tree will be just fine. But trees that are stressed or in decline may not heal, leading to insect or disease problems and/or internal decay that could make it necessary to eventually remove the tree. We can evaluate any trees that show signs of frost cracks and give you advice about how to keep them healthy and resilient to prevent future problems.

Landscaping and construction projects can easily break tree branches, injure tree trunks, and damage roots, leaving trees stressed, susceptible to insect and disease problems, or no longer stable after the work has been completed. Preventing these problems is always better than trying to fix them after the fact! So, if you have a construction or landscaping project planned, take some time to plan for the safety of your valuable trees before construction starts. This will help ensure your trees, and the surrounding landscape, continue to flourish. Conduct a Thorough Evaluation Before Work Begins The first thing you can do is document your site as it is by taking photographs. Document your trees’ condition and appearance before construction starts so, if any damage occurs, you have a way to measure it. Identify or number each tree and note its location on a drawing of your property (a hand-drawn sketch is fine). Then photograph the following: its surroundings, its root flare at ground level, its dripline, and its trunk and branch structure. Be sure to also photograph any existing damage or disease. Consider a Tree Valuation If you have valuable or heritage trees, or just vigorous, mature trees, a tree valuation inspection before construction may be a good idea. This is a process by which the monetary value of a tree is calculated, and its replacement cost set. If an accident occurs and you lose a tree, you’ll have a system for remediation or replacement. The needs of new landscaping and construction and the renovation of built-up sites are at odds with the needs of existing trees right from the start. Making a plan for your trees before, during, and after site construction is the best way to ensure their safety and health. Common Types of Tree Damage From Construction Like icebergs, there’s a lot more to trees than what you see above ground. A tree’s extensive underground root system is how it gets water, oxygen, and vital nutrients from the soil. Roots are also the anchoring system that keeps a tree securely rooted and able to withstand high winds and storms. All parts of a tree, both above and below ground, are at risk for damage from construction. Each phase of your construction project should have a plan that takes the protection of your trees into account. Damage To Tree Roots A tree’s roots are its lifeline and they are particularly susceptible to damage in project sites. A tree’s feeder roots take up food and water for the whole tree, and a tree’s anchoring roots keep it stable and safe in the ground. During construction, it’s important to protect those roots. Since a tree’s root system extends far beyond its trunk, this can be a large area to monitor and protect. The construction activities that most commonly damage tree roots include: Trenching for utility or irrigation lines, which cuts all roots that cross the path of the trench. Re-grading existing soil for drainage or new paving usually exposes root systems or severs roots, both which can be deadly to a tree Excavating soil around tree roots for new footings, foundations, or for a garden pond Soil tilling around tree roots to create new planting beds or for installing new sod What To Do Before construction, prepare a plan drawing that shows both existing trees and any proposed excavation, trenching, and re-grading. This can be used to decide where to install protection methods and to ensure you’re protecting a large enough area around each tree. Damage To Tree Branches And Trunks Construction sites are generally busy places, which increases the chance that a truck, excavator, cherry picker, or other heavy equipment may collide with an existing tree. In a match-up between tree and machinery, the tree always loses, resulting in damage to the tree’s trunk or branches either at ground level or in a tree’s crown. Tears and gouges to a tree’s bark are serious wounds as these expose the vulnerable interior of a tree to pests and diseases. These wounds require a lot of internal sealing off of the damaged area by the tree. Broken or ripped off tree branches can also cause serious damage and will require corrective pruning. What To Do Before construction, prune back or remove any low-hanging or wide-spreading branches that may interfere with construction. It’s better to cleanly remove a branch before damage occurs than to repair damage to a broken branch. Have tree protection installed around the trunk of all trees that are in or around a construction area. This visible tree protection lets crews know to stay away. Soil Compaction Because it’s invisible, soil compaction is often overlooked as a factor in tree damage, but it should definitely be addressed. Heavy vehicles and staging areas for materials can quickly compact soil, with wet or saturated soils compounding the problem. Compaction compresses soil particles together and prevents roots from growing, reduces oxygen levels in soil, and prevents water from penetrating the soil’s surface. For an established tree, these changes can be fatal. What To Do Before construction, lay out vehicular routes and staging areas, and make sure that their perimeters are flagged. Then add six inches layer of organic mulch or straw over these routes and top the mulch with strong plywood sheets or steel road plates. The cushioning layer of mulch will protect the soil surface and the rigid coverings will spread the weight of vehicles and materials over a larger area of soil, lessening the effects of compaction. Any additional protection, such as fencing and enclosures around trees should be installed at this time. Backhoe moving dirt and stones on a lawn, with a house and trees in the background Changes to the soil levels during landscaping or construction projects can impact your trees Changes To Soil Levels The top one foot of soil contains the majority of a tree’s roots and most of the water, air, and nutrients that your tree needs. Adding soil over the existing soil surface smothers roots by depriving them of oxygen, and changes how water moves through soil. Scraping off soil removes and exposes those same tree roots, and exposure to air will kill them. What To Do If your construction project involves re-grading your site for footings, foundations, driveways, or paving, be sure your existing trees are taken into account. Bring up any concerns about existing trees with your designer or contractor when your construction project is being designed. This will help ensure your designer includes tree protection as part of the site design’s constraints. Before construction, verify that your plans accommodate tree roots as much as possible. Even slight changes to the existing grade, either by adding soil or removing it, can damage your trees. If soil excavation is required, make sure any newly exposed soil is immediately covered by a tarp and kept moist. Tree leaves with sun shining behind Changes in the amount of sunlight a plant or tree receives can lead to issues Changes To Sun And Shade Levels You may not be able to prevent the construction or demolition of structures that determine the amount of sunlight that reaches your trees. In this case, the best thing you can do is help your trees to remain healthy; this will give them a better chance of successfully adjusting to their changed conditions. What To Do Before construction begins, ensure there’s plenty of tree protection installed around the affected trees. In addition to physical barriers, adding a layer of wood mulch over the trees’ drip line will help keep the soil temperature constant and reduce water evaporation. In hot weather, maintain an irrigation system for the trees to prevent heat and water stress. Do not prune the trees unless absolutely required for safety, and avoid high-nitrogen fertilizer that will stimulate leaf growth when trees are stressed. What To Do During The Construction Project During construction, it’s important to regularly inspect the site and make sure all your tree protection has been implemented and is being maintained and respected. All subcontractors should be familiar with your tree protection methods, and the general contractor should organize all project tasks to avoid damage to existing trees. Here’s what to look for and do during landscaping and construction projects: Check that tree protection is in place – Ensure all tree protection enclosures are stable and protect as large an area of a tree’s root system as possible. A tree’s drip line is a typical perimeter, but in this case more is better. If stakes, fencing, flags, or signs have been removed, relocated, or damaged, ask that they be repaired Remove debris – Debris should be regularly hauled away, and not left on site where it will take up valuable space. No debris should be piled around existing trees or “temporarily” stored. Minimize on-site storage – Material storage and staging areas should be cleared after each phase or subcontractor’s work is done, to lessen soil compaction and to keep space clear. Inspect any materials that might spill, dissolve, or leach into soil and damage trees to make sure they’re properly stored. Keep an eye on your trees – Verify that any work near existing trees is being performed correctly, that tree-friendly tools such as air spades are used whenever possible, and that any trenching or excavation work that requires inspection and approval has its soil volume replaced as soon as the work is approved. Communicate clearly – Reiterate to any uninformed crew members the importance of protecting trees. Document any tree damage – Document any damage to trees as you find it, and make sure your contractor is aware. Any corrective tree work should be done as soon as possible, and any damaged tree should be fully evaluated. What to Do When the Project is Completed When all construction is finished, walk through the site and document any changes or damage caused by construction. Comparing finished conditions to the “before” photographs will verify what’s new and what was existing. Here are some specific things to check: Check that all debris and construction materials have been removed, and that debris such as concrete has not been left in the soil where it can change soil pH. Check all new irrigation or water pipes to make sure they’re working as designed, and that there are no leaks that can saturate the soil around trees. Check around the trunk flare at the base of your trees to make sure that no “extra” soil from excavation has been spread over the existing soil. If so, ask to have it immediately removed to prevent root damage. Trunk flare on a tree before construction begins Check your tree trunk and roots to make sure extra dirt hasn’t piled up during construction – you should be able to see the trunk flare What to Follow Up on After a Construction Project You should monitor the health and vigor of your trees after construction is complete to ensure their seasonal growth patterns are continuing as usual and that they don’t exhibit symptoms of stress. If you notice any signs of decline, call your tree care professional right away to evaluate the tree. Your trees will also benefit from some additional care in the year after construction: Make sure existing trees have the same level of irrigation as they did pre-construction Keep mulch replenished around the base of your trees Apply compost to your soil for slow-release, long-term nutrients for your trees And monitor any tree damage so that if problems develop you can treat them right away. These include: areas where tree bark was gouged or removed, any pruning cuts that were made accommodate construction, and the overall appearance of trees where their roots may have been damaged. Some trees enter a period of slow decline after being damaged and don’t regain their previous vigor. However, with proper care, many trees will slowly recover and continue to grow for years to come. Ideally, both you and your trees will survive the disruption that construction projects cause and come out of the experience with a healthy, structurally sound, and beautiful landscape.