Lesson 1: Fruit Tree Biology
The internet is flooded with articles and videos about "How to Prune Fruit Trees". Simply showing you how to prune fruit trees will not give you the confidence that comes with truly understanding why and where to make pruning cuts that will be beneficial to your tree. I get it, it can be scary to cut a branch not knowing if that cut will cause irreversible damage to your tree.
In this lesson we will not bore you with a long scientific lecture about plant biology, but we will briefly cover the important parts of fruit tree biology that will help you better understand how to correctly prune your trees.
This is the first lesson of a 9 part fruit pruning course. If you would like to see the introduction to this course, please follow this link:
First, let's talk about photosynthesis. Don't zone out just yet! Photosynthesis is a simple process that plants use to make sugar...and fruit is full of the stuff!
Remember in elementary school your teacher would use a story like this to help you learn about addition and subtraction:
"There is a school bus with 10 children on it and four get off. How many children are still on the bus?"
Photosynthesis is like that story:
There were 6 water (H2O) molecules and 6 carbon dioxide (CO2) molecules. Using the light of the sun, your fruit tree converted those water and carbon dioxide molecules into 1 sugar molecule (C6H12O6) and 6 oxygen molecules (O2). See the diagram below.
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Why is this important for pruning? Because your fruit tree needs plenty of light and water to produce sugar and plenty of sugar to produce fruit, but before we talk about pruning, lets talk about how that sugar is used in your tree.
Think of your fruit tree as a solar generator. The leaves are solar panels, the branches are wires, and your tree's roots are the battery. Instead of generating electricity, your fruit tree is generating sugar.
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If leaves are like solar panels, they will be more efficient if they have full sun. Pruning your tree will allow your tree to receive more light at each leaf. Although pruning is best done in the early spring before the leaves emerge, It will help you to imagine each branch with leaves and prune away branches that will shade other branches. We will go into more detail about how to do this in future lessons.
Leaves need energy to produce sugar. Some of the sugar that they create is burned up in the leaf and the surplus is given to the branch that is holding the leaf. That branch will use the sugar it needs, and transfer the surplus to the larger branch that it is connected to, and so on, until the remaining sugars reach the trunk and end at the root system. Just like wires moving electricity to a battery, your tree's branches are moving sugars to your tree's root system.
Another way to look at this is to imagine the Mississippi River watershed. A small creek empties into a small stream. This stream empties into a small river, and the river drains into the Mississippi. The size of any one of those bodies of water is directly influenced by the amount of water that is draining into it. Likewise, the girth of a branch is directly influenced by the amount of leaves feeding that branch. It is not uncommon for the largest branches on a fruit tree to exist on the south and southwest sides of the tree because those are the sides receiving the most solar energy, and the canopy shades itself on the north and northeast sides, making that side of the tree weak and spindly.
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| Watersheds Look Like Trees |
Understanding this concept will help you to understand that you can control where, and how much your tree grows by the amount of solar energy your tree is collecting at the leaves. in the example above, where the southwest side of the tree shades the northeast side, you can aggressively prune one side and leave the other. This will slow the growth on the southwest side and speed up the growth on the northeast side, achieving a more balanced tree.
Alright, we did it! There is much more to learn about fruit tree biology, but this is really all you will need to know in order to master fruit tree pruning.
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I like to point out to people when guiding their pruning or explaining mine, that photosynthesis is where the tree combines carbon dioxide, water into sugar. The leaves near the fruit are the primary feeders of that fruit. The more sunshine the leaves get, the more effective they are at converting CO2 and Water into sugar. Therefore you need to prune the tree so that as many leaves as possible get as much sun as possible.
ReplyDeleteThank you for the clarification. Photosynthesis occurs primarily in the leaves and the leaves produce the sugars that are stored in the fruit.
DeleteIts the leaves where photosynthesis happens, not the fruit itself.
ReplyDeleteCorrect! Thank you for clarifying.
Delete