Pruning techniques to make your trees more resilient to winter storms
The temperatures have dropped, and it’s probably just a matter of time before we get some serious winter weather. The best thing we can be doing this time of year to make our trees more storm resilient is pruning. We’re going to walk you through the pruning techniques that will help a tree if and when we get another serious winter storm.
As we’ve seen more and more in recent winters, the combination of wind and ice will lead to branch failure—in short, nature prunes itself. That’s exactly why it’s best to prune problem areas now rather than waiting until snow and ice is predicted. Ice can increase the weight load on a branch by up to 30 times.
For an even more in-depth guide to pruning, visit our pruning page.
Prune outside the branch collar. The most important technique when pruning any branch, whether it’s a quarter-inch or four inches diameter, is to prune just outside the branch collar. On some types of tree, the branch collar is obvious. It is that bit of swelling—like a collar—at the base of where the branch connects to the trunk. That swelling is an accumulation of healing hormones. If you cut flush against the trunk, you’re cutting away the hormones that will close it off and protect it from pests and diseases.
Remove the Ds. The best way to start is to look for branches that are dead, diseased, dying, or decaying— anything that starts with a D. Just take a nice pruning saw or or some hand pruners and prune that right out of the tree.
A small six- or seven-inch folding saw is really all that a homeowner needs. We could do 99% of what we end up doing with just hand pruners and a folding saw on a young tree.
Mind your pruning budget. You shouldn’t prune away more than 25% of your tree’s canopy. Leaves are effectively solar panels that produce energy for the tree, and you don’t want to remove too much of that. Sometimes people want to prune their trees to encourage it to grow taller, and they’ll prune all the lower branches and make a sort of lollipop. So another part of calculation is that two-thirds of the trunk needs to have lateral branches.
Dead and dying branches do not count toward that budget, because they are not producing energy for the tree. The tree wants to lose those anyway and, as we already mentioned, nature will more recklessly prune them away during the next storm if you don’t. Suckers—the small branches at the base of the trees—should also be removed. While they do have leaves, they also do not count toward that budget, because they could become so vigorous that they just take over.
Look for included bark. A wide angle between a lateral branch and the trunk creates better architecture than a sharper angle. When the angle is more acute, the bark will start to fold over itself in the crease at the connection point. This is called included bark. Branches with included bark are where more than 80% of failures happen.
There might be instances where pruning all the branches with included bark will take you beyond your pruning budget, in trees like Japanese maples, zelkova trees, or columnar (upright) cultivated varieties. There are ways to address included branches without removing them entirely. You can cut away the most vigorous upright branches along the branch, which will stop that branch from growing more. There is a gravity-fed hormone in upright branches that encourages growth. By removing the upright branches, you change the hormones to those for repair and reproduction and in doing so, slow the growth of the branch relative to the trunk.
Encourage a strong central trunk. We’re trying to prune trees to have a strong central trunk—or central leader. Some trees, like conifers, grow a central trunk naturally. Other trees want to have a more rounded canopy. We want to create a strong backbone so that a tree is more resilient to wind. It is a bit unnatural, but when we are planting trees in the built environment, we have safety considerations to keep in mind. If a tree is in the middle of a giant backyard, it can take a more natural shape, but if it’s somewhere where its branches could fall on a house or a car, it’s helpful to have that strong central trunk.
When you prune, look for a strong central leader on a young tree that can be encouraged as it matures, and prune away competitive side branches. The rule of thumb is that you don’t want to have any lateral branches that are more than half the diameter of the central leader. By keeping those side branches smaller, if they fail, it’s less likely to be catastrophic to the tree or its surroundings.
If a storm comes!
When a winter storm does arrive, what do you do? Shake off snow, but not ice. Light snow can be gently shaken from branches with a broom moved in an upward motion. Heavier snow and ice should be allowed to completely melt because branches with ice especially often fail when shaken.
Once the snow is gone, inspect your tree for damage, taking care to take safety precautions as necessary. You can use a pruning saw to cut away any dead or damaged branches at the nearest branch collar.
- We have an entire webpage on how to prune that gets into even deeper detail.
- If you have a bigger tree, and the task of pruning it is beyond you, get in touch with one of these recommended arborists.
- If you have a specific question that you just can’t crack, you can write our new email address for pruning questions: firstname.lastname@example.org.
Last month, we told you why you should leave the leaves. We got such great feedback that we decided to create a regular tree care column, Leaflet, so that our eager experts can pass on their knowledge. We’ll share best practices for tree care and maintenance, explore common myths and misconceptions, and dig into the science behind it all.
“Now that the leaves are on the ground, we get busy,” says Neighborhood Trees Senior Specialist Drew Land about the November tree planting season. “Speaking of busy, roots are always busy.” We plant trees now so that while the trees are dormant above ground, they can focus on establishing their roots below ground. From timing to mulching to watering, our strategies help shape the tree’s root system.
“Street trees are not truly part of the urban forest until their roots start to intermingle,” Drew says. That’s why making sure a tree’s roots get established properly is a crucial part of planting and maintenance.
Because roots are almost entirely underground, we don’t really think about the shape of their structure. Rather than just a main tap root that goes straight down, 85% of a tree’s roots are within the top 24 inches of soil, or at least they should be. In the urban environment, roots are often up against the challenge of compacted and nutrient-depleted soil. In situations like these, roots will be too shallow, because they don’t have the space to seek out water and oxygen. Trees in the forest enjoy uncompacted soil with plenty of air and water spaces below ground. This also gives room for the fungal and microbial activity that brings soil to life.
“Roots are opportunists,” Drew says. “They follow the resources.” Given the right moisture and temperature, tree roots can grow year round. Insulation from mulch maintains those conditions, and we spread it in a way that encourages the roots to grow outward. Similarly, we shouldn’t just water at the base of a tree’s trunk, but should aim to water the tips of roots as they grow outward from the trunk. And we should water long enough that it sinks beyond the surface. Deep, infrequent watering mimics natural rain storms and gives roots what they need to spread both outward and downward. “Well-meaning people often shallow water on a daily basis, but that only feeds grass/weeds and not the tree roots a foot below. “
Tree roots come in two main types: structural roots and feeder roots. Structural roots are woody, and serve as the architecture to keep the tree upright. Feeder roots, which are much more like root hairs, are in charge of absorbing water and nutrients.
Maybe you have heard the myth that tree roots can grow into your sewer or water pipes and bust them open. Drew is here to officially bust that myth. He says that while roots are opportunistic, they are not invasive. “So the roots are not busting your sewer line,” he promises. “Your line is already busted and the roots found a tasty water source.”
Recreating ideal natural conditions is the best way to ensure that the roots of our urban trees stay healthy. “Roots are like muscles,” Drew says. “They grow in response to stress.” When you tie a newly planted tree too tightly to a support, it won’t have the freedom to move in the wind, building up those root “muscles” to support itself.
Getting the roots established is one of the most important reasons we plant new trees in the fall. “Planting trees now, while they’re dormant, will build their resilience,” Drew says. ”In ten months, when autumn winds hit their leaves for the first time, they’ll be ready.”
Leave the leaves!
Fall brings cooler days and evenings, an extra layer when we head out, and the striking colors on display gifted to us by nature. For many of us fall also means raking leaves–but it shouldn’t. In fact, fall tree care should include leaving the leaves!
We have this habit as a society to rake and dispose of leaves, but leaves are vitamins for plants and magic for building the health and vitality of soil. Throughout the growing season trees are producing energy in the form of sugar, or, sap. This time of year, as we start to see the leaves changing color, that’s the indication that the sap is crawling from the leaves, into twigs and branches, down the trunk and into the roots for winter.
When leaves fall, much of the tree’s energy, in the form of sap, goes into the root system encouraging new root growth (FOT gets busy this time of year very deliberately: planting trees now gives the roots a head start and a chance to anchor themselves). The rest of the leaf energy falls from the tree and settles on the ground–these leaves are literally vitamins for the root system that is primarily about 12-18” below the soil surface.
When we remove leaves we are actually interrupting a process called nutrient cycling, which is when the leaves break down and feed the roots. Rain carries the nutrients downward and provides them to trees and other plants water-solubly. So, leave the leaves! At the base of trees, in your garden beds, anywhere you want healthy soil in the spring.
Mulching: it’s not just for spring
Think about it: the forest floor is perfectly mulched. The act of transplanting a tree is unnatural, what we do planting trees doesn’t happen in nature, they don’t jump around and move. So, as tree stewards, we are trying to make trees feel comfortable, to restore a natural setting–as much as possible, of course, in an urban area. Street trees have it tough in this regard: They are often in compacted soil that is depleted, and it’s depleted because, unlike in the forest, we often remove leaves and clippings, and soil gets very compacted in the built environment.
So in addition to leaving the leaves, refresh mulch as needed. Create a “sacred mulched zone” ideally 2-3 feet in each direction from the base of the tree; this should be and remain a grass-free zone, and it should be an area that won’t be disturbed. If the tree is in a small space, such as a street tree next to the sidewalk, maintain it in the form of a square if there’s grass to mow since it’s easier to mow along a straight line than around a ring of mulch.
Why mulch? 50% of healthy soil is air & water pockets. How do we get these pockets? Partly through roots, just the process of roots growing down. And when some of the roots die and decompose they leave space in their wake, where fungi and bacteria grow and bring life to soil. Those fungi and bacteria grow where the soil isn’t, which is why compacted soil can be a challenge to bring to life.
When trees are transplanted – the most stressful day of a tree’s life – we want to foster new growth to set the new tree on the path of health and vitality. Tree roots can grow year round as long as the temperature of the soil is moderate (think of mulch as a down jacket for the soil) and there is the presence of moisture, both of which are provided by mulch! One inch of mulch is a windbreaker, three inches is like a down jacket – and we want that year round, protecting against temperate extremes. Not only is mulch insulating, it’s also thirst-quenching since wood chips hold water.
Fall tree care should start with building the soil with organic matter through application of mulch, setting the tree up for success, which is ever more important in a changing climate. Do take some time to get your mulching and non-raking done, and then tune in next month when we share the next stage of your fall tree care (hint: it rhymes with strewn, but don’t start yet!).
It’s hot out there! In our service area and around the world we are experiencing unprecedented weather events as a result of climate change, including a recent heat dome with multiple triple-digit days. Here are some helpful tips to help your new trees weather the heat!
In general trees in our area need water from April to October, depending on weather. As you may know, extended hot, dry weather can place a great deal of stress on trees. Fortunately, just a little extra care will provide your trees the relief they need to minimize drought stress and keep them healthy. Follow these simple steps to ensure your new trees have the support they need:
Established trees: Give them a monthly soak, perhaps an hour on a drip line, or more if the tree appears stressed (e.g., dropping leaves).
New trees (in the ground 1-3 years):
WATER: During an excessive heat event, we recommend that you double your normal watering routine. This means that your new trees should receive 15 gallons of water at least twice a week throughout the heat wave, meaning a deep watering every three to four days when it’s about 90-degrees or more for an extended period.
The best time to water is in the early morning or after the sun goes down to minimize water loss to evaporation. Water slowly so that moisture soaks deeply into the soil and doesn’t run away from the root zone. This can be achieved using one of the following methods:
- A slow-release watering bag
- A DIY 5-gallon bucket drip system (check it out in the video above)
- Trickle your hose within the root zone for 15-20 minutes
Be mindful that it is possible to overwater your trees as well (though unlikely during the Portland region’s dry summers, overwatering is more common when folks water trees in winter. Allowing the soil to completely dry out—or allowing it to stay soggy—will result in a tree that is stressed. Deep, infrequent watering is the way to go: Water deeply, then hold off. Healthy roots follow the water downward as it starts to dry and establish sinker roots for increased drought tolerance. Keeping the soil consistently moist through deep and infrequent watering is essential to healthy trees. Wondering if it’s time to water? If you poke a pencil 4-5 inches down, does it come out dry & dusty? If so, water!
MULCH: Organic mulch is a highly effective way to keep the soil from drying out quickly, especially during excessive heat. A thick layer of mulch from wood chips and ground leaves is even better: Wood is essentially carbon and carbon is nature’s sponge, and leaves are like vitamins that are taken into the roots and are water-soluble. What we offer at the FOT Portland office is ground up branches and leaves combined, just like what’s found on the floor of a healthy forest.
“I like to remind folks that the forest floor is perfectly mulched and your street tree should be, too!” Andrew Land, Neighborhood Trees Senior Specialist
Mulch around the base of the tree will help to retain soil moisture and regulate soil temperature, which is exactly what roots need to grow. Apply mulch for a newly planted street tree using the 3-3-3 rule: mulch should be at least 3″ deep, 3′ in diameter, and pulled at least 3″ from the base of the trunk. If your tree is beyond that first year, you can extend that mulch further because our objective is to mulch the tips of the roots as they grow outward from the trunk. Three-inches thick is also important because it’s insulation (imagine the difference between a wind-breaker and a down jacket, for example: that dead air space matters.)
PRUNING: Generally it is safe to prune most trees in mid-summer, from roughly mid-July to mid-August to be more specific. However, you may want to pause pruning during an extreme heat event, including right before and right after an extreme event, so consult the weather forecast as part of your pruning plan. Check out our pruning page for lots of useful information, including how-tos.
We’re seeing some gorgeous sunny spring days recently, which means…it’s time to start watering your young tree(s)! A newly planted tree needs at least 10-15 gallons of water each week from roughly now until late September for the first three years in the ground to ensure that they thrive going forward. Providing one deep watering over the entire root system per week is recommended. You can think of it as giving your tree a weekly rain shower – every Saturday morning, for example. If we have approximately 90-degree or warmer weather consistently or if your tree shows any signs of being thirsty (wilting, browning leaf margins, etc), it wouldn’t hurt to double up and water both Tuesday and Saturday that week.
There are a number of different ways to make watering easier. You can easily construct your own 5-gallon bucket drip system or purchase a 15-gallon slow-release watering bag (such as a gator bag). Please note we no longer will be offering these from the Friends of Trees as we have in years past, but that is because they are readily available online and in local hardware and garden stores. Also, be sure to check out our Tree Care page to get all the details on taking care of your new investment.
Remember that weeds and grass compete with your tree for water. Please maintain the mulch for your tree(s) and hand pull weeds. When you mulch, be sure that there is a 3-6” radius from the base of the trunk of the tree that is free of mulch. You want that space clear so there’s no moisture held at the base of the trunk, which can rot the tree’s root crown. The moisture held by mulch should be above the growing root tips as they grow outward from the trunk, for the most part within about 18″ of the soil surface. Also, please be careful not to damage the tree bark with lawn mowers, weed eaters, or car doors. The bark is what contains a tree’s water and nutrient transportation system; it also keeps insects and diseases out.
We have volunteer Summer Inspectors out visiting every street and yard tree planted in the previous season, and they keep us informed on the health of the trees we plant. If you have a tree that isn’t looking so great, please trust that after Summer Inspectors complete their routes this summer we will then determine if staff needs to check on your tree.
Portland Urban Forestry recommends an annual root pruning for trees planted in the streets, especially those in narrower planting strips, to discourage roots from growing under sidewalks. Here is a link to learn more.
Pay it Forward! Friends of Trees couldn’t reach our high goals without supporters like you. In order to continue providing tree discounts and plant in as many neighborhoods possible, we need your help! Please consider making a donation to help us grow our urban forest for both this and future generations.
Hopefully we’ve answered your questions and you’ve found these links helpful, but feel free to contact us if you have any questions at 503-595-0212 or email me at AndrewL@FriendsofTrees.org .