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Proper Pruning: Why Removing Diseased Branches May Not Be A Good Gardening Practice

Dec 03, 2010

We've been taught that "proper pruning" involves removing the 3 D’s from our trees: Dead, Damaged and Diseased wood, so our pruning chores tend to revolve around that.

I can definitely see how pruning dead wood that could be a hazard - such as a big branch in a tree that might fall on your house - is a good idea. If that tree is in a place where it doesn’t pose a hazard, pruning out the dead wood is not necessary, but even then it's okay to do if it's unsightly.

But it gets a little hazy when we look at damaged and diseased wood...


Proper Pruning For Damaged Branches

If 2 branches are seriously rubbing together, it makes sense to prune one of them out in order to prevent damage to both of them as they grow. Water sprouts and suckers can be pruned out, too, since they often develop into structurally unsafe branches.

Other damaged branches that still have green leaves, however, are valuable to the plant. The plant may still be photosynthesizing with these leaves and if it is a big branch or series of branches, it could be a big reduction in the plant’s photosynthesizing capacity to prune all of that out.

Or the plant may have abandoned photosynthesis, in which case it will pull many of the nutrients from those leaves back into another part of the plant where they can be used. If we prune too early, even if we’re using proper pruning techniques, we are not only creating an open wound, but we are removing many nutrients that still could be useful to the plant.

This is the case even with small perennials. They may look unsightly when they are dying back, but the longer you leave them, the more nutrients the plant gets to bring back into itself for use in the future.


Proper Pruning For Diseased And Insect-Infested Branches

Just like with damaged branches, even when covered in disease or insects, the leaves are often still photosynthesizing and we definitely don’t want to remove the photosynthesizing capacity of a plant while it’s being eaten by a pest. It needs all of the nutrients it can get.

Conventional thinking is that we can remove the pest by pruning out the infected branches, but this is impossible when you think about it. Billions and billions of the disease-causing organism or thousands of the insects live all over the garden. Removing a few branches does nothing to get rid of them.

But the most important shift in thinking we need to have is realizing the pest is not the problem. The problem is that our plant is unhealthy. If it were healthier, it would easily cope with the pest. If it were optimally healthy, it wouldn’t have any pests. Period. Here's why...

 
Why Do Diseases (And Insects) Eat Your Plants?

Why do "bad" bacteria, fungi and other protists (I will refer to all of these as diseases from now on) and insects eat plants? It all comes down to the same reason. We tend to think insects and diseases are making our plants unhealthy, but actually, they are there because our plants are unhealthy. This is one of the biggest shifts we need to make in our thinking when moving to organic gardening practices.

While animals prefer healthy plants, insects and diseases prefer the opposite. They choose plants that have either a deficiency of excess - a nutritional imbalance - of one or more nutrients. They literally do not possess the enzymes necessary to digest "healthy" plants.

In fact, they don’t even see healthy plants as a food source at all! Sounds crazy, right?

Well I'm going to explain it, because I think this is one of the most important and exciting concepts to understand. I won't go into too much detail, but here's the gist of it.


How Insects and Diseases Find Our Plants

Animals (like us) see in the visual light spectrum. Insects and diseases do a lot of their “seeing” in the infrared light spectrum. Insects, for example, do this by using their antennae and tuning into electromagnetic frequencies.

So in your organic garden, your sick plants - those that have a nutritional imbalance - emit a frequency in the infrared light spectrum that a pest "sees" and recognizes it as food.

Healthy plants simply do not emit these frequencies. So insects and diseases do not see healthy plants as a food source.

If our plants are sick and being eaten by pests, pruning out the pest does not give the plant the nutrients it needs to get healthy.


Proper Pruning to Increase Airflow and Light Penetration?

Plants have inhabited the earth for a few hundred million years. They’ve been here perhaps 1000 times longer than we have and in that time, they learned how to grow. Each species learned how big it should grow and exactly how it should arrange its branches.

The idea that we can improve upon that with proper pruning is kind of funny when you think about it, right? We are taught to remove branches, especially in trees, to increase air circulation and light penetration, but the plant knows how much air and light it needs.

All we’re doing is creating more wounds exposed to both the elements and predators, and decreased photosynthesizing capability. What about that branch that seems to go the wrong direction through the tree? The tree must have messed up right? I doubt it. The tree grew the branch that way on purpose, no doubt, in order to find the perfect balance.

We Prune for Weird Reasons

Much of the pruning done in residential gardens is for our aesthetic pleasure. We prune to make tidy shapes that please us. We prune shrubs to keep them nice and small to fit the place we planted them, when simply putting the right plant there in the first place would have been better.

And when it comes to pest-infested leaves and branches, we need to think twice before pruning them out. The plant may still need the photosynthesizing capability and nutrients from those leaves. You won’t remove the pest - you’ll just give it better access.

Organic gardening is about improving the health of the plant to the point where pests have no effect on the plant at all. That's what I teach at http://www.smilinggardener.com/organic-home-gardening

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About me: My name is Phil Nauta and I'm a SOUL Certified Organic Land Care Professional and hold a Certificate In Organic Landscape Management from Gaia College and a Certificate In Sustainable Building And Design From Yestermorrow in addition to a Permaculture Design Certificate. I've taught for Gaia College and been a director for The Society For Organic Urban Land Care. I've also run both an organic landscaping business and an organic fertilizer business before starting 'Smiling Gardener' to teach others what I've learned.
 

Comments

Thankyou Phil, This past year I planted 2 plum trees, 2 pear trees, and an apple. I,ve just ordered 2 peach trees for this year. All disease resistant varieties, cause I have no intention of spraying them. How much to prune is something I've been thinking about. I've done some reading including the "One Straw Revolution" and I really appeciate your article. I'll be reading this several more times.
I will be passing along your thoughtful & pithy insights. Our best arborists here agree with you. Last fall we had an early, heavy & wet snowfall that broke many trees in town. Pat Rainey, of Arbor Care, came by to assess pruning off the big, ragged breaks in a medium-sized, mid-age, multi-stemmed Box Elder tree in the street easement. A south part of the tree had broken off & the north side was already extra-bushy & leaning toward a tall, mercury-vapor street light, as if from photo-tropism. I thought this would be a good chance to "balance" the tree. I was actually surprised that he mildly but firmly demurred to cut anything but the ragged breaks, for the very reasons you have expressed so well. I thought I was sensitive to plant life, but Pat showed me greater sensitivity - having suffered such trauma, the tree will need all the leaves it has to recover - was his point of view. I have never given a bush a haircut, but earlier I did describe pruning my Gravenstein apple trees - which became magnificent, productive trees in their maturity. But now I wonder if my annual shaping held back their first blooming until their 11th year! http://kitchengardeners.org/group/apple-tree And I know I lost two Apricot trees because I gave them a spring shortening-pruning in a year when we had experienced a record -38F degrees below zero. After the extreme winter temps they just couldn't push out new growth on older wood. I think they would have made it if I had left their newer tip growth. Confession & reflection time ...
Hi Phil. My name's Brendan. I'm a certified arborist in Canada. This is an interesting article, but I'd like to point out a couple of fallacies and oversights you've made. To start: ["I can definitely see how pruning dead wood that could be a hazard - such as a big branch in a tree that might fall on your house - is a good idea. If that tree is in a place where it doesn’t pose a hazard, pruning out the dead wood is not necessary, but even then it's okay to do if it's unsightly."] While it's true that pruning of smaller deadwood is not necessary for the health of a tree pruning of larger deadwood is necessary to promote tree health for one very good reason; It makes a tree more susceptible to attacks by pests and pathogens. Trees are very good at walling off dead and diseased parts, however those walls can be compromised as a result of the failure of the dead part or wounding by insects and animals which may be attacking the deadwood. ["Other damaged branches that still have green leaves, however, are valuable to the plant. The plant may still be photosynthesizing with these leaves and if it is a big branch or series of branches, it could be a big reduction in the plant’s photosynthesizing capacity to prune all of that out."] It is true that green leaves do provide valuable photosynthetic material to a stressed tree, however it should be noted that any broken part of a tree will become diseased. Furthermore any damaged part is liable to attempt to replace the lost photosynthetic material through the production of water sprouts. Water sprouts are problematic because they become very heavy very quickly and are poorly attached to the tree. If they are growing on a limb that is already damaged and will begin to decay the problem is compounded. It is far better to remove the broken part of the tree to a proper pruning point and let the tree spend use the energy it might put into producing water sprouts at the wound into replacing the lost foliage at a more appropriate location. ["Or the plant may have abandoned photosynthesis, in which case it will pull many of the nutrients from those leaves back into another part of the plant where they can be used. If we prune too early, even if we’re using proper pruning techniques, we are not only creating an open wound, but we are removing many nutrients that still could be useful to the plant. This is the case even with small perennials. They may look unsightly when they are dying back, but the longer you leave them, the more nutrients the plant gets to bring back into itself for use in the future."] This is actually much more the case in small perennials. In larger maturing trees the amount of energy stored in leaves is minor since most energy is stored in the roots prior to dormancy. It could even be argued that, because of reduced sunlight availability in the late season, extraneous foliage becomes much more of an energy sink and draws valuable nutrients out of the roots where it would be better off being stored for spring. ["Just like with damaged branches, even when covered in disease or insects, the leaves are often still photosynthesizing and we definitely don’t want to remove the photosynthesizing capacity of a plant while it’s being eaten by a pest. It needs all of the nutrients it can get. Conventional thinking is that we can remove the pest by pruning out the infected branches, but this is impossible when you think about it. Billions and billions of the disease-causing organism or thousands of the insects live all over the garden. Removing a few branches does nothing to get rid of them."] Actually the reason for removing the infected part of the tree has less to do with removing the pest that's attacking it and more to do with removing the part that is infected. Pests attack parts of a tree because that part of the tree is stressed. This stress can be caused by disease (most likely as a result of a wound) or because that part of the tree is not getting enough energy. The main reason a part of a tree isn't getting enough energy is that it's being outcompeted for sunlight either by other trees or by neighbouring branches on the same tree. We don't prune infected branches to remove the infection. We prune them to remove a part of the tree which uses more energy than it produces. ["But the most important shift in thinking we need to have is realizing the pest is not the problem. The problem is that our plant is unhealthy. If it were healthier, it would easily cope with the pest. If it were optimally healthy, it wouldn’t have any pests. Period."] Which is precisely why proper and regular pruning is essential. ["If our plants are sick and being eaten by pests, pruning out the pest does not give the plant the nutrients it needs to get healthy."] Technically no, it doesn't. However pruning out the infected part of the plant removes an energy sink thereby increasing the amount of nutrients available to the healthy parts of the plant. ["Plants have inhabited the earth for a few hundred million years. They’ve been here perhaps 1000 times longer than we have and in that time, they learned how to grow. Each species learned how big it should grow and exactly how it should arrange its branches."] This is true to a point. Plants that grow in your back yard are not growing under the same conditions that they have for hundreds of millions of years. Trees growing naturally tend to do so closely surrounded by other trees. Because they have to compete for light and space forest trees are very frugal with foliage production. The produce very slender upright stems and leaves mainly at the top. Branches at the bottom are small and quickly shaded out. Another thing to remember about trees growing in a forest is that, except for edge trees and the few tallest trees, they are not subject to a great deal of wind. These are the growing conditions the lone maple tree in your back yard has evolved to cope with, and they are very different from what it's forced to cope with in an urban setting. ["The idea that we can improve upon that with proper pruning is kind of funny when you think about it, right? We are taught to remove branches, especially in trees, to increase air circulation and light penetration, but the plant knows how much air and light it needs."] This is patently untrue. Plants don't have a nervous system, so, unlike a human being, a tree never gets a feeling of being full, it simply continues to produce branches and foliage to collect as much sunlight as it can until it can no longer produce enough energy to maintain the mass of it's structure. This is the point at which it begins to decline. Generally speaking the faster a plant grows the sooner it reaches this point. Proper, regular pruning slows down the growth rate of plants by regulating the amount of energy available to it. In a forest this happens naturally as limbs die off as a result of competition. Regular, proper pruning prolongs life. ["All we’re doing is creating more wounds exposed to both the elements and predators, and decreased photosynthesizing capability. What about that branch that seems to go the wrong direction through the tree? The tree must have messed up right? I doubt it. The tree grew the branch that way on purpose, no doubt, in order to find the perfect balance."] Actually the tree grew that branch there, because, at the time, there was sunlight available there. Balance never entered into it. As for producing wounds, wounding from regular branch shedding is a normal, natural part of a tree's life. In a natural setting branches tend to be shed while still small as the forest canopy prevents rapid growth and shades them out quickly. Not so with urban trees. Pruning of branches before they become too large and heavy and fail (often resulting in larger wounds that compromise the compartmentalization of the main stem) is a key component of regular urban tree maintenance. The tree is perfectly capable of compartmentalizing the wounds. I suggest at this point that if anyone doesn't know or understand what CODIT is they should research and understand it before they begin pruning any trees or woody plants. ["Much of the pruning done in residential gardens is for our aesthetic pleasure. We prune to make tidy shapes that please us. We prune shrubs to keep them nice and small to fit the place we planted them, when simply putting the right plant there in the first place would have been better."] I couldn't agree with you more. Wrong tree, wrong spot is a very common problem I have to deal with in my line of work. However I will argue that regular pruning (ie not topping) is an effective way to maintain a large maturing tree in a confined growing space and can result in a very interesting tree. Bonsai trees are an extreme example of this philosophy. The key is in understanding how a tree grows and reacts to how it is pruned. ["And when it comes to pest-infested leaves and branches, we need to think twice before pruning them out. The plant may still need the photosynthesizing capability and nutrients from those leaves. You won’t remove the pest - you’ll just give it better access."] I disagree. If the plant still needed the photosynthetic capability of the infected part the part would be strong and healthy. It is precisely because it is a drain on the energy reserves of a plant that a branch becomes susceptible to infection. Pruning of an infected part to a proper pruning point (being a main leader or a lateral branch no less than 1/3 the diameter of the part being removed, and in a way that does not compromise the walls of CODIT) will not, in any way, provide greater access for a pest or pathogen. Organic gardening is about using biological methods to maintain a beautiful garden. One of the best ways to ensure that non-biological chemicals need never be used on your trees (with the added benefit of extending their life-span) is to have regular preventative pruning done by a skilled, knowledgable and certified arborist.
It's no wonder I always have phoenix tree removal come and remove my dead trees, I definitely don't prune them right.... I think I might have been a little too eager to cut branches that I removed too many. If I really want to keep growing trees in my garden, I should better keep your suggestions in mind from now on ...

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