University Place

Plant Pruning Basics

[gentle music]

Cora Borgens: All right, hello, all, and welcome to “I’m Cutting You Off, or Plant Pruning Basics.” We will be covering a lot today. I kind of crammed almost a whole college semester into a one-hour presentation. But like Tina was kind enough to say, this presentation is recorded, so you can go back and watch it later. And please hold all questions ’til the end. I’ll have, I’ll leave as much time as I can to go over them, otherwise I will hang around outside after the presentation as well.

Cora Borgens: To start us off, hello, my name is Cora. I graduated from Washington State University with a degree in integrated plant sciences. I have to give kudos to one of my professors and my school mom, Carol Kawula, whose teachings were the foundation of this presentation. While in school, I interned at the Sarah P. Duke Gardens in Durham, North Carolina, which really solidified my love for botanic gardens and public gardening. My first job out of college brought me to Wisconsin and almost didn’t keep me here, but I found such an amazing community that I couldn’t bring myself to leave. I currently work in the medical field, but I’m working on the side in science communication and freelance horticulture. I’m a cat mom to two furry scoundrels, and I knit prolifically in every minute of my spare time.

Cora Borgens: So some topics we’ll cover today. We’ll talk about why pruning matters. Why do we worry about it in the first place? We’ll talk a little bit about pruning equipment and basic info about what to use and when to use it. We’ll talk about some plant anatomy, looking at how plants grow so that we can best understand how to prune them. Tree injury and compartmentalization. Another facet of plant anatomy that gets its own section due to how important it is. And how to exactly make your pruning cuts. We’ll talk about plant growth types and pruning, because how the plant grows naturally will affect how you want to prune it. And finally, we’ll have a short little section on pruning conifers because they’re a little bit more tricky to prune because they grow a little differently.

Cora Borgens: So to start off our first section, why pruning? The definition of pruning is the removal or reduction of parts of a plant for a variety of reasons. Some of those reasons can include pruning to enhance or restrict size or form of the plant, form meaning shape. We can prune to prolong the future health of a plant or to renovate old plant growth. We can prune to train a plant for future growth. Usually, this has to do with pruning trees. Pruning to enhance flowering or fruiting of a plant. To ensure safety in the landscape. This is huge in a public setting, but just as important in your own backyard. And finally, pruning to help a plant serve a specific purpose in the landscape. It could be a shade plant, a privacy screen, or pruning to increase airflow or light to an area.

Cora Borgens: In general, the desired pruning outcome for most landscape plants is for the plant to not look like you touched it in the first place. So we have this saying in landscape design and landscape management, “You wanna put the right plant in the right place.” So a design goal is that you wanna maximize the plant size to fit its desired volume. But when this doesn’t go quite right, pruning can help us take control of the situation again. For example, the image on the left there, the shrubs are fully grown, but they’re not overgrowing the pathway. On the right, that shrub has gotten too big. It’s now in the pathway and is a hazard to your eyeballs. We don’t want that.

Cora Borgens: Pruning can be done when plants are actively growing or when they’re dormant, and some plants prefer it when actively growing versus when they’re dormant. Winter pruning is fun this time of year. There’s a few benefits to this, so plants are ready to start growing really quickly in the spring. As soon as the temperatures warm up, they’re gonna push out a lot of new growth. This means if you make your pruning cuts now, they can seal off those wounds pretty quickly and start pushing out new growth as soon as spring hits. Winter makes it easier to see any issues with your plants, especially with deciduous trees where the leaves might be covering up problems. But now, with all those leaves gone, you can see what issues there might be and plan what you wanna do for your pruning. And winter tends to be a less busy time for you and for landscaping professionals, though not always. But regardless, it’s a good time to just kind of walk around your yard and make notes of what you might wanna do come springtime.

Cora Borgens: Some things you wanna watch out for. You don’t wanna prune if there’s a hard frost forecasted. If temperatures drop rapidly while that pruning wound is still wet and open, the freezing temperatures can cause that moisture to expand and will cause damage to those plant tissues. Some plants are known as bleeders. Sap can leak out of their pruning cuts, and so you want to avoid pruning them this time of year. Some examples of bleeders are birch, elm, dogwood, walnuts, and maples. Where do we get maple syrup from? Maple trees. What time do we get maple syrup? About this time of year because that sap is flowing early. So if you were to prune a maple this early in the spring, it’ll start this bleeding or leaking the sap. It looks scary, but I promise it does not hurt the plant.

Cora Borgens: Some other things to watch out for are your early spring bloomers or fruiting plants. So these plants set their buds at the end of the previous growing season, and those buds sit on the plant and sit dormant all winter until those temperatures start to warm up. So if you prune them right now, you’re cutting off all those lovely flower buds. You wanna wait until after they’re done blooming in order to prune them. And the same goes for early fruiting plants, because fruit comes from flowers, so you don’t wanna take off those flowers.

Cora Borgens: Pruning is one of the most frequently misunderstood practices directing plant growth. You need to have an understanding of the plant’s natural habit or its natural shape. You need to know the biology of the plant, like when it sets flowers and fruit. And finally, you need to understand what role is the plant playing in the environment? Is it a privacy screen? Then you don’t wanna prune too aggressively. You want that nice dense growth. Is it a specimen plant? Well, then you want to prune it to show off its structure or its flowers.

Cora Borgens: So moving on to our pruning equipment and using the right tools to make the cut. It’s important to have the right tool for the job. This will reduce the chances of injury to you and/or to the plant. You wanna buy the best equipment that you can afford, or that you will reasonably use. Better quality means it’ll last you a long time, theoretically, but there’s no sense going out and buying an expensive piece of equipment for just one landscaping job. There are lots of tool rentals available for larger equipment through your local hardware stores. For example, my husband and I just bought a new house, so I want to rip up my entire front yard to get rid of grass and just plant it with other plants. I’m not gonna buy a rototiller to do that because I’m only gonna need to do it once. So I’m gonna do a, I’ll rent the equipment when I’m ready to tackle this project.

Cora Borgens: Your most common pruning tool is going to be your hand pruners, shears, clippers, secateurs, whatever you wanna call them. You know what they look like. I would recommend you get a very good quality pair of these because you’re gonna be using them a lot. They’re most frequently used for annuals, perennials, and small branches. You want the stem to be able to comfortably fit in the width of the blade, so that you can make a nice clean cut. Anything larger that you’re trying to cut, you’re gonna have a hard time getting all the way through it, which can make it harder for the plant to seal over a jagged wound. And you can also risk damaging your pruners. Believe me, I have bent blades trying to cut through. Just, I’m like, “I can get this one little water sprout.” No, I bent the blades. It was a cheaper set. It wasn’t my good pruners, but still.

Cora Borgens: There are a couple different types of hand pruners you’ll see. The most common type is the bypass or scissor action pruners seen in the top image there. These can cut cleanly through live plant material because the blades overlap right at the end. The other type is an anvil or snap cut pruner, which is used only for dead wood because the blade comes down into a little groove. And so as you apply pressure to a dead woody stem, it’s more likely to just snap off at that point. If you try using anvil pruners on live material, that live tissue is gonna get squished down into that groove, and it won’t cut all the way through.

Cora Borgens: Loppers or two-handed pruners allow you to cut larger branches and stems and give you a little more reach into dense shrubs or above head for some branches. You still wanna be aware of your blade size, and make sure you’re cutting stems that appropriately fit into the blades. It’s good to look for a pair of pruners that have bumpers or a cushioning mechanism near the blades. This is a little easier on the tool and a little easier on your joints, and it’s also helpful to look for a removable bolt so you can replace the blades when needed. These also come in bypass or anvil type, and also a ratchet or gear-driven action, which snaps into place gradually as you close the blades. It can allow you to cut through tougher wood or larger pieces of wood with a little bit less effort.

Cora Borgens: Hand pruning saws, I would say, is my number two tool behind your hand pruners. These allow you to cut even larger branches, usually two inches in diameter or more. They’re easy to maneuver in tight branch crotches or in shrubs that have lots of large stems very close together. Some come in a curved design that’s meant to cut on the pull stroke. It’s a little bit more ergonomic. They come either as a static or non-foldable blade, seen in the top picture, or in a foldable design seen in the middle picture. And these ones lock into place when they’re fully open, and then you press the button, and they lock into place when they’re fully closed. Make sure this locking mechanism works so you don’t accidentally cause injury to yourself by it opening or closing when you don’t want it to. Again, I’m speaking from experience.

Cora Borgens: Some other tools you might encounter are hedge trimmers. These are meant for the very small twiggy stems and shaping your shrubs. These can be hand-operated or powered. Pole pruners are kind of like loppers, but on a much longer pole. These allow you to reach branches high up in a canopy. Again, these can also be hand-operated using a little pull rope or powered. And finally, your chainsaws. These are for three inches or larger diameter branches and most often used for large pruning jobs or the removal of entire trees, shrubs, limbs, that sort of thing. Hopefully not your own limbs. If you’re using a chainsaw, never use it while you’re standing on a ladder. It’s not a stable base, and if you have a chainsaw, consider also buying a pair of protective chaps so you don’t hurt your legs. You only have two legs, please protect them.

Cora Borgens: Maintenance is an important part of extending the life and efficacy of your tools. Make sure to clean your tools after every pruning project, removing any dirt or sap that could gum up or dull your blades. Sharpen the blades when needed, usually once a season. Winter is a great time to sit down and sharpen your blades. Oil your blades as needed to make sure your pruners open and close smoothly, and oil them before you store them for the winter just to help prevent rusting. Always store in a dry location, again to avoid rusting, and replace your blades if they get any serious nicks, or if the blades become bent out of shape. If there is a nick or a bend in the blades that does not allow them to completely close all the way, you wanna take care of that. And a lot of, a lot of hand pruners, the companies that produce them also make replacement blade sets that you can buy.

Cora Borgens: Sterilization is probably not going to be an issue for most of you, as this is more common in agricultural or research practices, but it can be useful if you do have a disease concern with some of your plants. So bacterial or fungal diseases will often spread through plant tissues or saps. So you want to sterilize between each plant that might be a vector or a source of disease transfer. You can sterilize using strong isopropyl or rubbing alcohol or a 10% bleach solution. That’s one part bleach to nine parts water. It’s usually enough to kill any bacteria or virus that you could be transferring. If you are using a bleach solution, remember to give your tools just a quick rinse with regular water afterwards because bleach can corrode metal.

Cora Borgens: So now on to plant anatomy. I am a plant nerd, and this is where my love for plants is is in how they grow and looking at the inner workings of them. But we need to know plant anatomy and understanding how our plants grow so that we prune them appropriately. So starting off very basic, there are two types of plant growth. There’s primary growth, which is your green, herbaceous, soft, tender growth. It’s usually growth in length or height of a plant and is growth from the shoot tips. This usually occurs in the first growing season for a plant, so plants such as annuals that only have the one growing season are likely going to be this tender herbaceous growth. Then we have secondary or woody growth. So this is when the plant starts to produce wood. This is associated with growth in the diameter or width of the stems. This always occurs after the primary growth. Biennials and perennials, plants with more than one growing season, can exhibit this secondary woody growth.

Cora Borgens: Now, I’m not gonna test you on this portion. This is just to point out a couple of things. The only parts I want you to pay attention to are the buds. At the end of a stem, we have our terminal bud. Sometimes there can be more than one, and any bud below that is a lateral or axial bud. Two names mean the same thing, so any bud below the terminal bud is a lateral bud. There are also bud scale scars. So it’s kind of a row of those little lines. And that’s just where the terminal bud from the previous growth season was. And so looking at the space between that bud scale scar and the one before shows you how much growth occurred in that season or the terminal bud and the last bud scale scar. That’s how much growth occurred in your last growing season.

Cora Borgens: Bud arrangement just tells you how buds are sitting on the stem. Opposite arrangement means they’re sitting directly across from each other, and alternate arrangement means they alternate which side of the stem they’re sitting on. This also will reflect what the resulting growth will look like. So if these buds start to grow, those branches will then be opposite or alternate.

Cora Borgens: Apical control and apical dominance are just functions directing how a plant grows. Both are terms for how upward growth, terminal growth, will stop lateral, or outward growth, from occurring. If apical dominance is broken, it will signal the lateral buds below it to start growing. So you cut off the top, and the lateral side buds will grow. It’ll get a little bushier. If apical control is broken, the lateral stems will try to take the place of the main leader. So instead of growing outwards, they’re gonna kind of change direction and go upwards. The plant’s form will be noticeably altered if the plant exhibits apical control and you break that main leader. It’s just gonna look different afterwards. It can’t really get that original look back. This is common with things like evergreen trees.

Cora Borgens: So how do trees grow? This is just a fun little picture. It’s not the same tree in both pictures, but it is a fig tree. So how does this tree start out? Every branch starts out as a bud. Branches then grow outwards and increase in diameter along with the trunk as year to year, they grow these woody layers. So, the branch wood is locked inside the trunk wood because these layers overlap. So you get a layer of branch wood and a layer of trunk wood. And so they overlap as they get bigger, and that locks the branch nice and secure to the rest of the trunk. It’s not like you had a clay model, and you had a trunk, and you just stick your little branch on the side. As these layers overlap, it creates a little area called the branch collar, or where the wood is just slightly more swollen right before that branch meets the trunk. And this is an important feature when it comes to pruning.

Cora Borgens: How do we know if a branch is strong? Branch diameter should always be less than half of trunk diameter. Anything more than that and we get into something called codominance. So I’ll get to that in just a little bit. But we wanna look for a branch that is less than half of the trunk’s diameter. Strong branches also should just occur at one location on a trunk. You shouldn’t have multiple branches kind of all at the same height or right next to each other, because as they get larger and increase in size, they’re gonna start to rub against each other and cause wounding, which could then cause some wood decay.

Cora Borgens: However, you wanna picture how these branches are gonna grow as they get older. This is a healthy branch attachment on this white pine, because as the trunk increases in size and as these branches increase in size, they’re so spread out that they’re never gonna interfere with each other. So this is an example where there are more than one branch at one spot, but they’re still healthily and strongly attached.

Cora Borgens: So, codominant stems are when a trunk becomes two or more branches or trunks of about the same size. This leads to a forking or a “Y” shape. And this creates a weak union between the branches, because instead of the smaller stem interlocking with the bark of the larger stem, they’re gonna continue to grow separately and without that interlocking support. This can become a problem, because those areas where they don’t quite overlap can allow water and microbes to get inside and start to decay the wood, and worst-case scenario, this could lead to the entire trunk splitting in half, which is a death sentence for this tree.

Cora Borgens: So, codominance can include, can mean you have included bark. So as these two stems grow separately, their bark is gonna kind of get trapped in between the two of them. It won’t somehow magically merge together. And like I mentioned earlier, that included bark can leave space for water or bacteria or fungi to get in there and start to decay the wood. Alternatively, we can have excluded bark, which is where the bark is pushing out and away from the trunk. This is what will naturally happen when we do get those overlapping layers and the bark continues to grow on that outer layer, and it just pushes outwards. So you can usually see the difference. It might be more subtle depending on some trees, but you can see where that bark is pushing outwards. And that’s healthy for branch attachment.

Cora Borgens: Water sprouts and suckers, otherwise known as epicormic growth. So, you’ll usually see these on trees. They’re just, some trees do this because they’re more aggressive growers. And sometimes they can do this in response to stress, not having enough water or something like that. But what they are are vertical shoots formed from stems or branches, in which case they’re water sprouts, or formed from the base of the plant, in which case they are suckers. These stems are always weakly attached. Because they grow so vertically, it’s hard to get those overlapping layers. They can become stronger with time and proper care, but you can also just prune them away any time of year.

Cora Borgens: So, what do we wanna look for for developing a strong tree or seeing if a tree has a strong foundation? So, our first characteristic for maximum stability in a tree is that the tree has a single main leader. It only has one trunk running the majority of the way through the plant. Once it gets to the very top canopy, it can kind of split and diverge, and you won’t notice it as much. But as long as it’s at least three-quarters of the way through the whole plant, you’re gonna have a strong base.

Cora Borgens: You wanna look for root flare at the base of a tree. So this means the roots have spread out and formed a really nice foundation and they, they’re really gripping the ground for that tree to hold steady in weather events. What can happen if the tree doesn’t have a strong root flare is in planting, if it’s planted too deep or covered with too much mulch, these roots are trying to find oxygen. They’re really important for oxygen exchange for the plant. And so as they’re covered, they’re gonna circle around the base of the tree and cause what we call girdling. So this is when the roots are circling around. It can happen because the plant wasn’t, or the tree wasn’t planted properly. And these girdling roots can kind of suffocate that tree as it tries to grow larger.

Cora Borgens: The next thing we wanna look for for stability is trunk taper. This just means that the caliper, or width of the trunk, is larger at the base and decreases as you move upward. A proper taper develops from a tree having enough time to grow and being able to move back and forth in the wind when it’s younger so it can kind of build up these woody layers at the base to strengthen it. So something like trees in a dense forest canopy, they’re gonna grow really quickly to try and reach that sunlight, and so their resulting wood can be weaker. They don’t have as strong of a trunk taper. Another thing that can weaken trunk taper is leaving your tree staked for too long. You only wanna leave them about a year, maybe two years. After that, you wanna take away those stakes and let the tree move around in the breeze, let it develop that trunk taper so that it can be strong into the future.

Cora Borgens: And the last thing we look for for maximum tree stability is making sure our branches are scaffolded, or evenly distributed. This occurs both in the vertical aspect, so as you’re moving from the base to the top, and in a radial aspect, so if you were looking top-down or bottom-up, making sure branches are evenly spaced all the way around. This is also what we’re looking for when we’re talking about that branch attachment and making sure that not too many branches are clustered in one spot, because this can mean the weight is unevenly distributed.

Cora Borgens: If the weight is unevenly distributed, the tree could be more prone to splitting or leaning to a specific side. The picture on the right shows a tree that has been lion’s-tailed, which is an outdated pruning practice where all of the interior branches are taken off, leaving only leaves at, like, kind of the tips of the branches, which puts the weight only out on those tips of the branches, and so those branches split. And, again, scaffolding is a structural feature that you wanna establish really early in the tree’s life and continue to maintain it, because it’s much harder to fix later. So the picture on the left here, it’s gonna be really hard to fix that uneven weight distribution. You’re kind of just gonna have to let it be or wait until you’re ready to take off that whole limb or take the tree down.

Cora Borgens: So, a quick little example. Do we have a strong main leader? Just a yes or no. Yes, this tree has a very clear leader directing its growth. How about root flare? Yep, this tree has good root flare. I like this example, because it’s very easy to see. Sometimes it can be a little more subtle. How about trunk taper? Yes, again, a little harder to see, but the width, or the width of the base of the tree is wider than further up. This tree is not surrounded by anything else. It had a lot of time to grow at its own pace, per se. And finally, what about our branch scaffolding? Yeah, this tree has really good branch scaffolding. There may be spots where it’s a little bit less thin. And, of course, there’s leaves over it, so you can’t see. But the overall shape of that tree’s crown, or leaf canopy, is very even. So it’s not leaning too heavily to one side.

Cora Borgens: All right, and now we’ll get into tree injury and compartmentalization. And a fun little saying I have here is animals heal, trees seal. And that grows for other plants as well. They can only seal. So, pruning inherently causes a wound to a plant. It’s important to know how plants deal with these wounds, especially for such longer-lived organisms like trees. Trees are some of the largest and longest-lived organisms that we know of. Despite this, they don’t have any wound-healing process. They can’t take damaged tissue and make it function again. They can only seal off these damaged areas and then grow new, functioning tissue around it. So an example of this are when wildfires leave scars on that are visible in tree rings even hundreds of years later. And this is an important part of dendrochronology, or dating things using tree rings.

Cora Borgens: So, how does a tree do this? Well, they have a process of creating boundaries around an injury both horizontally, radially, and vertically inside the trunk. So every direction that something could go, the tree has a way to block that pathway off. This helps resist the loss of normal wood function, which is strength and transporting water or nutrients, and helps resist the spread of bacteria and fungi that can cause decay. The tree will then grow new wood around this area and eventually close over the top of these boundaries. This process is called CODIT, or compartmentalization of decay in trees, coined by Alex Shigo of the USDA Forest Service.

Cora Borgens: One specific zone that can form is in the base of a branch, we have what’s called the branch protection zone. This area has more chemicals in the wood that resist microorganisms from spreading. So what this does functionally is if a branch is injured and starts to decay, it can decay down into that where that branch wood is. But because we have that separation with the branch protection zone and the layers of the trunk wood, that can stop that decay from moving into the trunk.

Cora Borgens: This can also work, so, it can work in two directions. It can also work where the center of the trunk is decayed and starts to hollow out. But you can see in that upper picture that that’s where the base of the branches are. That’s where that branch protection zone is. This is why it’s really, really important not to harm the branch collar or those overlapping layers when you’re making your pruning cuts.

Cora Borgens: And speaking of making pruning cuts, how do we, how do we actually do it? Well, we have two types of cuts that we use. The first is a thinning cut. And a thinning cut is used to take off a lateral branch where it joins a larger branch or where it joins the trunk of the plant. And this then directs the growth to that other main branch. And then, there’s a heading cut, which interrupts that growth pattern and often induces other branches to grow.

Cora Borgens: So, for heading cuts, growth is localized to each specific stem. It can force lateral buds, or those lower-down buds from the terminal buds, to grow on most plants. It results in very lush and vigorous growth. But those new stems might be weakly attached. They tend to have that very vertical growth, kind of like water sprouts and suckers.

Cora Borgens: Heading cuts are good for increasing the fullness of your shrub. So instead of having one stem, or in the picture, instead of having six stems, when you cut it, then it has 12, and it’s gonna increase exponentially like that. So it increases the fullness of that shrub. So you wanna use heading cuts when you’re shearing. It’s inherently what you’re doing. You can also use heading cuts to force buds at specific locations. And it’s useful on smaller branches. We’re talking finger thickness or less. The larger the stem diameter, the more aggressively this plant is gonna sprout out from the area that you made the cut. You can also use heading cuts for rejuvenation of certain shrubs. And rejuvenation is when you cut all of the stems off. You cut everything down and start over. Which you do need to do for some plants on occasion. And heading cuts can be used to increase flower production on plants that produce their flowers at those terminal tips. So instead of having one stem, if you cut it off and get two or three, well, that’s two or three more flower buds than you had previously.

Cora Borgens: So when we’re actually making a heading cut, you wanna cut slightly above a bud or set of buds. If you leave it too high, the chunk left behind until you get to those buds is gonna decay, and that decay could possibly move further down the stem. Cut it too low, and you could accidentally harm these buds, and then the growth is gonna have to revert back to the next set down, and you’ll end up with the first problem. For alternate bud arrangement, you wanna go just above a bud and cut at about a 45-degree angle. This just allows water to roll off that stem. And for opposite-bud arrangement, you wanna go just above the buds and then just cut straight across.

Cora Borgens: Please, please, please, please, please don’t use heading cuts on trees or tree topping. This is when you go through and remove the tops of the entire… All the way across the tree, the branches and trunks, you’re taking the top of everything off. You’re gonna have that really vertical growth afterwards. So, our consequence of this, we don’t have any branch protection zone to protect our tree, so the branches and trunk could possibly start to rot away. It’s very much going to stress out the tree. You’re taking away a lot of its energy, and you’re, it’s gonna cause a lot of new growth, which also takes energy until it can get those leaves back. And it will ruin the natural form of this tree. The tree will never recover its original shape.

Cora Borgens: So we have very poor growth resulting from this. And this new growth is prone to breakage, especially if it’s left to get larger. So if it gets larger and heavier and then it breaks off, now it’s a safety hazard in addition to being really ugly.

Cora Borgens: Thinning cuts are when we remove a branch back to a larger branch or back to the trunk itself. What happens when we do this? It means the growth effect is distributed over the entire plant. We are just redirecting that growth. We’re not causing the plant to grow new stems that it wouldn’t previously. It keeps the same growth pattern.

Cora Borgens: A proper thinning cut happens just outside the branch collar. We don’t wanna hurt that branch collar. And this is in contrast to a flush cut, which is where you would cut perpendicular, or parallel, excuse me, parallel to the trunk. And what happens when you do this is you destroy your branch protection zone. It’s a larger area that the plant needs to seal over. And remember, things like trees, they grow pretty slowly. So you wanna cause the smallest wound that you can so that it can seal over quicker and you have no barrier between the branch wood and trunk wood. So if this decay that’s starting to happen, it will inevitably happen with wood, that can then start to move down the trunk. And in a matter of years, possibly decades, it could compromise the entire tree. Again, it’s not gonna happen right away, but it’s not a good, you’re not giving that tree any help into its life.

Cora Borgens: And this is just another diagram of cutting outside the branch collar. And it’s also demonstrating a three-point cut, which is what we’re gonna talk about next. So, what a three-point cut does, it’s a method for cutting larger branches that prevent them from tearing into the bark and possibly tearing into the branch collar and branch protection zone. So this area of torn wood is susceptible to decay and will take much longer for the tree to seal over. Again, that’s a much larger area that’s now exposed. And do you see what else is wrong with this picture? They also made a flush cut. So they made a flush cut, which already wasn’t good, and then the branch tore the bark further down. So that’s gonna be a really hard wound for that tree to try and seal over.

Cora Borgens: What we do with the three-point cut is wherever you want your final cut to be, you’re gonna move a few inches out. And I would say, you know, the further the distance for however big the branch is gonna be. If it’s a small branch, maybe just four to six inches. But your first cut is going to be a few inches away from where you want your final cut. And you’re gonna cut from the bottom up. You’re gonna start at the bottom. And what this does is relieves the weight of the rest of that branch, preventing it from tearing backwards. And what happens is you’ll usually know your saw getting, notice your saw getting pinched in the wood. It’ll get harder to move it, because that weight is shifting down onto it. Your second cut is to go just outside or just a little bit further out from your first one, and just cut downwards until you cut all the way through or until the branch naturally snaps off. So instead of tearing, it’s just gonna snap at this one spot, and then it’ll fall off. This relieves the weight of all the rest of that branch, leaving you free to make your third cut, which is where you want your final cut to be initially. And you only have to deal with this little stub, so it’s not as much weight you’re trying to wrangle when you’re making your final cut. It can be very clean, which it, makes it easier for the plant to seal over. And when you do this process right and it snaps off perfectly, oh, it’s so satisfying.

Cora Borgens: So, plant growth patterns and pruning. First of all, when you’re pruning anything, you wanna prune in small doses. Take off a few pieces, step back, get the larger picture, and then go back in for more. You can’t put anything back on once you take it off. When we’re pruning, we always wanna remove the three Ds: any dead, damaged, or diseased parts of the plant that could impact how it’s growing in the future. We also wanna remove any crossing or rubbing branches, because these are gonna cause damage and possibly decay in the future. And we can remove any water sprouts or suckers. And this is just a little diagram of what you can be looking for when you’re looking at a tree canopy.

Cora Borgens: So, we have three different plant growth types, and each one is gonna affect how we want to prune that plant. So, our first type is terminal growers, like most trees. Our second is basal growers, which covers most of your shrubs. And finally, we have intermediate growers, which are partly like basal growers and partly like terminal growers. So you can prune them in either direction, depending on what you want the plant to look like.

Cora Borgens: So, for our terminal growers, most trees, these usually have a single trunk. They might have a couple, but usually they have a single trunk. Their largest buds will be at their terminal tips, and their growth is most prolific from those terminal tips of the stems. Most pruning work starts at a young age. And again, almost all trees are terminal growers.

Cora Borgens: So, our steps to pruning these, first, remove your three Ds: any dead, damaged, or diseased wood. Then you wanna remove any wrongly placed, interfering, or rubbing limbs. So these are things that might be pointing in the wrong direction. They might be rubbing against each other or going to rub into each other when they get a little bit bigger. Then you can prune to shape, establishing your good scaffolding, making sure branches are evenly spaced. You’re gonna kind of imagine what this plant is gonna look like as it gets bigger. You only wanna use proper thinning cuts, taking every stem back to a larger branch or back to the trunk itself. And in general, don’t prune more than a quarter to a third of the total branches on the tree or you’re gonna start stressing it out. Pruning removes the leaves for that plant, which leaves generate energy. So taking away too much of that, and in addition, the plant having to spend energy to recover, you don’t wanna take off more than a third of everything that’s there or you stress your plant out.

Cora Borgens: Our basal growers, so most shrubs, they have multiple trunks or stems from the base. They usually have their largest buds on the more middle portions of the stem, and they flower on these more middle or lateral portions of the stem. We usually prune our shrubs to enhance blooming or fruiting, and we can also prune to keep them from getting too crowded. If they get too crowded at the base, the stems could, again, rub against each other, or you could get some leaves and other material down in there that starts to cause decay, which could, you know, make it harder for the plant to repel that decay. Common basal growers include forsythia, boxwood, spireas, any shrub that has a lot of stems that come out from the base.

Cora Borgens: Our pruning steps for basal growers, again, start with the three Ds. Then we wanna remove one-third of the oldest stems at ground level. Not one-third of all the stems, just a third of the oldest, largest stems. This helps thin out the base of that plant and make space for those smaller stems to grow bigger. Then you wanna stand back and cut any unappealing stems. So if you have one that’s way taller than the rest, go ahead and go in and take that one out. If you have one that’s growing a weird direction or had some damage, so it’s growing one way, and then it starts growing a different way, you can take those out. You just continue thinning things out in a random pattern until, again, a quarter to a third of all the stems are removed.

Cora Borgens: Shearing works well with basal growers because we have those flowers all along the stems and not just at the ends, so your heading cuts won’t remove all of these flowers. Shearing shrubs can increase the “twigginess,” or fullness. It will still remove some of the flowers, but you’re gonna have a lot left behind. It will, however, cause the shrub to lose its natural form. Usually, we are shearing a shrub into a specific form. You can get this back over time, but it’s gonna take some work. And additionally, causing a lot of little pruning wounds all over the plant could potentially make it more insect- and disease-prone. It’s usually not gonna be an issue, but it is something to factor into account. And finally, shearing is very labor-intensive. You have to do this multiple times a growing season. So if you’re paying someone else to do this, you’re gonna have to pay them a lot more to do something like this. And also, it’s more work for you, and I don’t think it results in a very good-looking plant. I would much rather have the plant in that top picture that looks nice and natural. It’s the same plant in both pictures, just not in the same place.

Cora Borgens: And finally, we have our intermediate growers. So growth for these is partly terminal and partly basal. They can have multiple stems at the base, but they also tend to have their largest buds at the terminal tips. So we wanna prune these to enhance flowering and fruiting. We prune to keep a specific form, so you can either keep them more as a shrub or keep them more as a tree, depending on how you want to prune them. And common examples of this are our lilacs, rhododendrons, some viburnum and hydrangea species.

Cora Borgens: And how we prune these, again, starting with the three Ds. And then, for our second step, you wanna decide what shape you want. If you want a basal shape, you’re going to take out a third of the oldest branches to leave the rest to grow and leave it nice and bushy. Or you want to remove all stems except your main leader or a couple main leaders, like you see with some lilac trees. They might have two or three main stems, but everything smaller than that coming from the base, you wanna remove. You can use heading cuts to force branching in certain areas. So if it’s maybe a little lopsided, you can go through, make a little cut to cause it to push out a couple stems and rebalance out. You can also use heading cuts to remove old seed and fruit heads. Because these have such larger flower heads at the ends, we can go through and take those flower heads off when they’re done blooming. And finally, use your thinning cuts to remove any unappealing stems.

Cora Borgens: Vining plants can also be pruned like intermediate growers. It really depends on what the plant is. So you might need to do your research into specific vines, when they flower, that sort of thing. They can be a lot more complicated. It’s more personal per plant.

Cora Borgens: And finally, we can do a rejuvenation pruning. So, this works on some shrubs. And what happens is we cut a plant completely to the ground. We use heading cuts all over the plant. This is useful for multi-stem shrubs that haven’t been pruned for years. They might be overgrown, leggy. They’re not flowering or not showing their bark color. Common example is your red-osier dogwood, or red-stemmed dogwood. The red is brightest on those young, on the youngest stems, and they get darker over time. So, on occasion, you might just decide, “Hey, it’s kind of tall and leggy. I just wanna cut ’em all off and get a bunch of those bright, new, fresh stems.” I wouldn’t recommend doing that every year, but you can do it every couple years. Rejuvenation pruning works on these basal or intermediate growers. It does not work with all plants. Please do your research before you do this so you don’t accidentally cut everything down, and then you’re left going, “Oh, no, what now?” [laughs]

Cora Borgens: For pruning annuals, you’re most commonly just gonna be deadheading and that sort of thing. Deadheading means to cut off spent flower heads or flower stalks, usually to prevent fruiting or seed formation, because that takes a lot of energy. So if the plant is directing all its energy to making seeds, it’s not gonna be making as many flowers. So you can save the plant some energy. And also, when you take off those parts where it’s trying to form seed, the plant can recognize, “Hey, I didn’t make my seeds. Let me send out more flowers so I can make my seeds.” Because that’s what they want to do.

Cora Borgens: You can also cut back annuals, so clearing or cutting away most or all of dead plant material in the fall, winter, or spring. You can do this for annuals or herbaceous perennials. However, removing green leaves, even if they’re mostly dead, that’s still some extra energy the plant is getting back. So I would recommend waiting until all of the leaves are completely withered, or wait until spring to do your spring cleaning.

Cora Borgens: Additionally, slow down on your spring cleaning. Don’t do this beforehand. Because leaving that, those leaves and dead plant material can provide habitat for our native invertebrates and pollinators. It helps give your plants some extra insulation against our really harsh winter temperatures. And it’s a good natural fertilizer. Leaves are nature’s best fertilizer. So wait to clean out your plant material until the insects are up and about in the spring, and then you can remove things. Leaving wet, decaying material can cause disease pressure for a plant. So once it starts growing, then you can clear out some of that and just give it a little bit of an easier time.

Cora Borgens: And our last section, pruning conifers. So, they have a little bit different pruning needs. They can be a little more tricky. Most conifers grow best in full sun. When the conifers become shaded, the foliage dies. So things like arborvitaes, if you look into the center of them, there’s no green leaves in the middle. They’re all on the edges, because that’s, there’s no point in the plant sending energy to those inner leaves if they’re not gonna get any energy in return from the sun. An exception to this, conifers that do handle shade well, are yews and hemlocks.

Cora Borgens: Additionally, most conifers have little to no capacity to grow back from old wood. So, this is what we call latent bud potential. So, in that example of tree topping, when we cut those tops off, they sprout from what are called latent buds, or buds that are dormant underneath the wood. Most conifers don’t have these latent buds, so they can’t grow back from old wood. Again, an exception to this are yews. Yews have pretty good latent bud potential.

Cora Borgens: Many conifers also have extremely strong apical control, so they can look really strange if you cut or damage the main leader. So, on the right is an example where the terminal leader has been cut out. And that shape’s gonna look weird. One of those branches might curve upwards and try and take its place. But it’s not gonna ever have its original shape. As you can see on the right, something happened to the main leader here, and it had three or four other branches kind of take its place, but that’s not the original shape that that tree had. And in addition, those curved branches, that weight’s gonna be a little bit unevenly distributed. And they’re more prone to breakage if you have a heavy snow or ice load.

Cora Borgens: Because conifers don’t sprout new growth in the same way that other plants do, sometimes they will leave your pruning areas visible. So, this is something like a blue globe spruce. They’re notorious for this. What you wanna try and do in this case is hide that pruning cut behind another branch that’s sitting in front of it, just to kind of hide that area. It’s more of an aesthetics thing. It doesn’t have any impact on the health of the plant.

Cora Borgens: This isn’t an embedded video, but it’s a great little primer into pruning conifers, with good examples of manipulating the plants’ growth. If it’s like a weeping conifer or a dwarf conifer, this has some good examples. It’s called “Pruning Conifers with Adrian Bloom,” from Bressingham Gardens. It’s just a great little video.

Cora Borgens: So when we’re actually pruning our conifers, we’re gonna do it kind of on a species basis. And you don’t have to know the species, but we’ll kind of base it off of the leaf type. So, pruning pines, pines come in packets. Their needles are bundled into a papery sheath. These grow from terminal buds and from undeveloped buds located on the stem where there are needles. Pruning below that on older wood won’t have any resulting growth. The plant can be kept small or kept a little bit dwarfed. If you start pruning when the plant is young, this isn’t something where you say, “Oh, this plant’s too big. I’m gonna cut it down really aggressively.” It’s not gonna regrow from that.

Cora Borgens: You wanna prune your pines in the spring, when they are candling. So, the way pines send out their new growth, it’s all kind of bundled together. It almost looks like a candlestick. So you can prune a third to a half of the total candle. This just leaves material behind so that it can keep growing in the future. And you still want to use your thinning cuts and your three Ds to take out other material on the plant.

Cora Borgens: Pruning firs, spruce, or true cedars. These are plants that have needles, but the needles tend to be a lot shorter, and they’re not bundled together. Buds here are located also at the tips, and on current season growth. If you reach the hard, woody stem, you’ve gone too far. It’s easier to prune these guys when they’re dormant, because then you can see exactly how much was current season growth. And so as long as you don’t take all of that off, you’ll be okay. You still wanna prune for good tree structure. The one on the left has, like, three competing main leaders. So take two of those off, pick one. And you still prune for the three Ds.

Cora Borgens: Pruning junipers, arborvitae, red cedars, and false cypress. So, these are plants that have scale- or awl-shaped leaves, so their leaves might be very short and prickly, or they might be kind of flat and scaly. You can prune these guys in late spring to early summer, because you only wanna prune where there are green leaves present. That’s where their buds are. Again, if you hit brown wood, you’ve gone too far.

Cora Borgens: Shearing is sometimes done with these guys because of their shape, but it can be very difficult. Shearing over time will create a very thin shell of leaves around an entirely brown and twiggy center. So you only wanna shear these when they’re actively growing so that you know you’re not taking away too much.

Cora Borgens: And finally, our hemlocks and yews. These have good latent bud potential along stems for many years. This means that you can cut into that brown wood and it can sprout afterwards. These are good for shearing because it’s okay if you go a little bit too far. And even those areas, if you shear back and you hit that kind of brown center, well, once that stem gets light, it can send up new buds. So these are the easiest types of conifers to keep small or keep hedged. And they can be cut during active or dormant periods, any time of year, really.

Cora Borgens: So, I just have one practice example here. Here’s our tree, or part of it anyway. And the first thing I’m seeing with this tree is that it’s just about codominant. And that branch is too narrow to the trunk. It’s gonna have some Oh, there’s our width there. It’s gonna have some included bark down where that red circle is. And where the blue circle is is where it’s kind of getting squished together, in the process of having included bark. So what we’re gonna do, I would take that entire branch off. Now, because of how small this tree is, that’s probably my one-third of the overall material for that tree. So I wouldn’t do hardly anything else for this tree unless it’s already dead or damaged material that I’m taking away. Additionally, this one had a good example. I know we’re taking off that whole stem. But this just has a good example of what I meant when we say awkwardly growing or awkwardly placed branches. It’s kind of growing across and outwards. Over time, it could rub into the trunk there, so you could just prune it where that little yellow line is.

Cora Borgens: All right, now we have time for questions.

[audience applauds]