A Pruning Primer

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The Virtual Bonsai tool had me thinking about how we might be able to use it to discuss pruning a real tree.

We discovered in a previous thread how bad online forums can be at TEACHING. It's time to find out how good they can be!

In this lesson you'll learn some of the terminology used to discuss branches and problem branch formations. You'll also learn a bit about how a tree grows and the system of balances that keep these problems in check.

Soon, we'll have an assignment and a test, so stay tuned!

Here's our test subject: Sharpen your virtual concave cutters, and we'll begin!

STUDYING THE TRUNK

In practice, the overall review begins with identification of the primary trunkline. The trunk of an informal upright ideally shows both movement and taper. This Virtual Bonsai tree, by design, has a rather obvious trunkline and with mild taper. We would inspect the tree from various angles and choose the potential "front" that offered the best compromise of the following:

1. Root display
2. Rise (angle) and taper of the lower trunk from the soil
3. Movement of the trunk along the existing (or potential) trunkline
4. Arrangement of branches

We'll assume for now that we have identified the view below as the "front" with the most immediate potential. Later, you will be able to use information in this article to identify and correct problems in the branching, and this will contribute to your skill in selecting the "front" of a tree.

Attached Images

virtprune_before.jpg (13.0 KB, 377 views)

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ESCAPE or SACRIFICE BRANCH

Branch A is very low on the trunk. Low branches like this may tend to make the plant look more like a shrub than a tree. Our first inclination might be to prune it off; however, low branches like this can be useful under certain circumstances:

1. one might be tempted to leave it on as an "escape branch" to help increase the caliper of the trunk! Some call it a "Sacrifice Branch" because it will be grown on to sacrifice later. "Escape" means that the branch is allowed to escape the design - or the pruners - with the intention of removing it at some point in the future.

2. A very low branch might serve as a secondary trunk in a multi-trunk design.

HINT: A tree's trunk at any given point will thicken in response to the foliage load ABOVE that point. If you want the trunk thicker, you may keep an out-of-position branch to help the trunk develop as you want it to.

Attached Images

virtprune_a.jpg (8.9 KB, 362 views)

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Branches C & B form what is known as a "Bar Branch" that is branches directly opposite one another on the trunk.

Sometimes they are also called spoke branches if three or more branches originate at the same level on the trunk, because they resemble the spokes on a wheel. Pines have this natural growth habit, but spoke branching usually takes care of itself in nature as the less successful of competing branches is shed. A growing tree produces many more branches than it requires or can sustain. Each branch is an opportunity and a liability to the plant. In nature, those that turn out to be ill placed and don't receive adequate light or ventilation will die off and ultimately be lost. We need to keep this fact in mind when we design a bonsai to ensure that the branch spacing and placement promotes good ventilation and light gathering capability to ensure the health of each branch.

Q: Are Bar Branches always Bad?

A: In some situations a bar branch might be acceptable: if, perhaps the branches differ in thickness, or you don't have many branches on the tree to begin with, a bar branch may be a necessary evil. With large bar branches or more than a couple branches in a given position, you may run the risk of creating a localized swelling in that area of the trunk. It's unsightly and hard to disguise later, and it could ultimately lead to reverse taper.

Q: We seem to have more than enough branches here. Which should remain in the final design?

A: Knowing we have a lot of branches in this area we needn't keep the bar, we need to look at another configuration to know for sure which is preferred:

Attached Images

virtprune_bc.jpg (6.5 KB, 359 views)

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POCKET BRANCH

Branch B forms at the inside of a curve, or "pocket" in the main trunk and is called a "pocket branch" So C would be preferable. It forms at the outside of the curve. Why do trees grow this way...throwing off branches at what appears to be close to the apex of each curve? Think of the branch as a leverage point and the trunk growing away from it provides balance to the design.

Similar to Bar branches, a Pocket branch may serve a purpose in a design. If there are no branches in that area of the trunk, a pocket branch may be a preferable alternative to a tree with a foliage void in an unfortunate position.

Attached Images

virtprune_b.jpg (8.9 KB, 356 views)

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PARALLEL BRANCHES

Perspective is hard to see here, but let's say branch D appears right above branch C and parallel to it. That's a bad configuration because branch D shades the trunk at C. Branches which naturally developed like this would be shed. In this case, we will keep C out of respect for its placement and prune away D.

Q: Are there times when it is appropriate to keep a parallel branch?

Note that branch D is shorter than branch C, so the effect is not nearly as bad as if the opposite is true. At least branch C could be assured of getting some light on its terminal. If branch D could be coaxed around to the rear of the tree with wire, that would be an acceptable treatment as this tree has no significant back branching.

Attached Images

virtprune_cd.jpg (9.2 KB, 352 views)

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MORE BAR BRANCHES

You've probably recognized E-F as another bar configuration. This time the trunk swings the opposite way, so Branch E would be in a better position. If you look closely branch E is a bit thick. We'd like to see a bit thinner branch at this position, so we might trim branch E back a bit to keep things in check.

E is our best option.

Attached Images

virtprune_ef.jpg (5.9 KB, 341 views)

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In this example lecture, you should have learned the following

1. How to recognize problem formations of bar, spoke, parallel, pocket,

2. What a sacrifice/escape branch is and how it functions.

3. How trees grow in a balanced arrangement, with the primary branching tending to form at the outside of curves in the trunk.

4. Why these "problem" formations are undesireable

5. How to eliminate these problem formations by branch selection and pruning.

6 You should have a grasp of circumstances under which you might keep an out-of-place branch

GETTING READY

Bone up a bit and we will have a practice assignment in the next couple days where you will need to decide which branches you'll keep and why. In the meantime, please feel free to ask questions about the examples above.

AFTER:

Here's an overall "after" view of this tree. That leaves us with something like the following tree. (Leaving Branch "A" on would be a logical thing to do to thicken the trunk, but I left it off here to show something of a cleaner design.

Also, this tree certainly lacks an important back branch Unfortunately in a 2D environment it is difficult to capture perspective with the "Virtual Bonsai Tool" so I will have to emphasize that the importance of rear branches in creating depth in your design.

Regards,

Matt

Attached Images

virtprune_after.jpg (9.8 KB, 337 views)

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plant_dr27

Thanks for the lesson, Matt. I learned a lot!
Regards,
Zach

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ripsgreentree

Because my trees tend to be under 20 in. I would remove A and chop the trunk at the bar branch B & C.
C would become the first branch and B would be come the new leader. This would allow me to set the line and movement of the trunk above the first branch.

Glenn

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