Okay, perhaps I defoliate too much. Maybe or maybe not. I can admit it before an audience. And, of course, there are those bonsai professionals out there who say, quite reasonably, that to cut off all a trees leaves might not be the best thing, horticulturally speaking. It seems, from a common sense view, a reasonable position to take. I mean, even an astrophysicist can deduce that a tree without leaves isn’t functioning very well, you know, photosynthesis and junk. But I have observed the results of well timed defoliation on healthy trees and can attest that it works (obviously we are doing this on broadleaf trees, not conifers like a juniper…). And it doesn’t bother me when I’m denigrated by these professionals because my trees show results, and other bonsai artists work gives credence to the defoliation technique. But recently I got a message from a Reddit user from Australia who was in a heated debate on one of the Australian forums about a specific technique of partial defoliation for elongation and thickening of a branch. I didn’t have the sciencey words to help him out so, in my “asking why” way, I decided to visit the scholarly articles facet of Google and get those answers (interesting place, the realm of “Scholarly Articles” it’s like the “dark web” where, if you find yourself in it, it’s probably best to back yourself out slowly, because if you stay, you might learn something that you didn’t want to know, like, say, all things are chemicals, even dirt…or we live in a heliocentric planetary system, and your worldview will change)
This post will be a talk about hormones (not the teen spirit kind, but the plant phytohormone kind). And, with my Google University diploma in hand, load up on guns, bring your friends, we begin. (See what I did there?)
As usual, my homilies contain trees I’m working at the time, so…….
So you’ll have to wait until the end to see tree number three. Don’t worry, I’ll mesmerize you so with my English language mastery and with staggering use of scientific jargon that you’ll forget my lackluster photography for this post. And it’s lacking, trust me.
Here’s the after pic of the second tree:You can read all about its history Here. It’s come a long way but I’m still not liking it much. That’s all the photos on this tree. A before and after. Time to get fancy with the science speak. Let’s turn our jaded gazes to this podo:
Everything you wanted to know about it (and podocarpus) is contained in the blogpost herein. It’s progressed quite a bit from when I first got it from my friend Reggie. In case you didn’t know, there are several podocarpus leaf sizes out there. This one is a big leaf variety. These two pics are from the blog post up there hyperlinked with the word “herein” you should read it. I’ll wait. I’m going to perform two defoliation techniques on this tree to get smaller leaves. The first is to cut the leaves mostly off and to nip the growing tip. Which is what I did totally to the 2nd tree. I’m pushing for ramification on it.
There are five main plant hormones, they are: auxin, cytokinin, gibberelins, abscisic acid, and ethylene gas. There are others and there are actually several different variants of each hormone (except ethylene). But I’ll only be talking about the ones that matter. Or the ones that help my argument, I am as susceptible to confirmation bias as the next guy, or gal. Or whatever he/she/they pronoun you prefer.
Auxin-everyone knows this one, right? It’s the hormone responsible for apical dominance and phototropism. It’s synthesized in the growing tips and travels downward (using energy, I should add). It activates the process of differentiation of vascular tissues. It also, in conjunction with cytokinin, is responsible for wound healing.
A quick aside, when we are talking plant hormones, we are talking minute amounts. In example, if we use two different auxins mixed together, and spray a forest or jungle in massive amounts, we don’t get a monster super tall tree jungle, we call that mixture Agent Orange and we get a wasteland. It’s actually toxic to plants in high concentrations (and birds and mammal and soldiers, women and children) even though it’s made by plants. Next!
Cytokinins– they come from the root tip and travel upward the same way water does, using no energy. They promote cell division. But they need auxins to work in tandem with. More on that when I present my grand thesis.
Gibberelins– they are like a cross between auxin and cytokinin. They promote cell division and cell elongation. Usually stem growth between nodes. They are in leaves and bud tips.
Abscisic Acid-technically, all the hormones are acids, so I’m not sure why they add acid to this one. Maybe it’s the alliteration. Scientists surely sling stupid sing-songy and sometimes salacious soliloquys sometimes. It forms in the bud tips but it’s job is to inhibit cell growth, say, when it’s time for a tree to go dormant. It also works in conjunction with ethylene to close stomata when a tree is dry or to abort leaves under stress conditions. It also stimulates root growth when water is scarce.
Ethylene Gas- if you know about tomatoes and green bananas, then you know about ethylene. It’s what’s responsible for fruit ripening. But, in our case, vegetatively, it stunts growth. It’s created when trees’ leaves are damaged someway, either through mechanical trauma, bugs, disease. More on that later too.
This one is all authoritative looking and stuff with my hand posed holding the scissor. That pic was before I cut off all the leaves. That’s the one branch that’s younger than all the rest. It’s an important branch needed to fill in that area on the and mature fast. The way I accomplish it is to defoliate everything but the terminal buds. It works; here’s how: By not pruning the terminal bud, it keeps the auxin intact, pushing length, I am not touching the roots, so the supply of cytokinin is stable, which keeps the ratio to auxin in an ideal stasis and encourages cell division and, therefore, girth. The damage (pruning) releases ethylene gas, which, with the presence of auxin, suppresses side growth. The lack of gibberellins (which are in the leaves, now defoliated) keeps the internodes shorter. Ethylene decreases gibberellins too. I learned the technique from Jim Smith, and it’s been confirmed by generations of tree farmers trying to get taller, thicker trees as fast as they can.
Now, to my regular defoliation technique. On a healthy tree, at the right time (all depending on species) I will defoliate and cut the terminal buds. What does this do? It increases ramification, it decreases internode length, it makes leaves smaller. How? Why?
Here we go, either on to the greatest explanation in the history of bonsai or the most facile, ignorant defense ever presented, of my technique. Here’s a very poorly illustrated diagram of our green hormone factory.
Here’s what happens when one defoliates, and tip prunes, without a repot.
First, the growing tip is gone, so the action of auxin is stopped, no more branch elongation, but, since we have roots still producing cytokinins, they do their job and push cellular division. Backbudding, so to speak. The effects of ethylene (stunting new growth) is also lessened with the lack of auxin. Gibberellins, which cause elongation of stems (the spaces between internodes) are also lessened because of the defoliation, therefore you get shorter internodes, what we want on the branches.
Abscisic acid, which is created and causes dormancy in leaf buds, have been lessened from the defoliation, and that action is halted. But that abscisic acid in the roots is untouched. As well as the cytokinins, which are also synthesized in the roots. They can now do their job in pushing cell division and backbudding, since auxin isn’t blocking its action.
The ethylene gas slows the growth, and you get smaller leaves.
For those Internet goobers who put the tl;dr (which means, too long; didn’t read): defoliation causes back budding, shorter internodes, smaller leaves.
Here is where I put some caveats: the tree should be healthy, the tree will try its best to do what the hormones are telling it to do, but if it is unhealthy or lacks the energy, it will grow (or not grow) itself to death.
Defoliation should be done at the right time, and the frequency matters. For example: a deciduous tree should be done mid summer, after the spring leaves have hardened off. Usually only once a summer unless you do it early summer and then late summer, but only if your growing season is long enough and the winter dormancy is great enough.
A broadleaf evergreen should be done in early spring after a repot (wait, a repot?! Don’t worry, I’ll get to that in a bit) and mid summer, then, depending on your climate, early fall (I can get away with it, but maybe not you. Winter begins in mid January for me and lasts through late February).
With tropicals, I might get four defoliations a year. You all in the frozen north, maybe only two or three. Come to la Florida, the livin’s easy.
I mentioned repottting with broadleaf evergreens on the first defoliation session. By cutting the roots at that time, we slow the synthesis of cytokinins, which slows the cellular division, but also it reduces the effects of ethylene and therefore the action of abscisic acid (which is created in both roots and leaf buds). Basically, you are keeping the hormones balanced. This mitigates stress to the tree and let’s it grow normally after the repot.
It’s a little hard to see what I did on those podocarpus so here’s a ficus to make it easier to see. It’s a tree that belongs to my niece. Earlier in the spring we trunk chopped it and repotted it. As you see it now, it is after branch selection and partial defoliation. I left all the growing tips but I need to slow the growth on some branches. Some wire and branch shortening. If you notice, I bent the tips up. This helps the auxin know which way is up.
A few more things about hormones. They are influenced by temperature and light. Auxin is responsible for phototropism, a plant growing towards the light (or away from the dark. The plant scientists aren’t quite sure the how or why yet, mainly because the amounts or hormones in a plant are so low it’s hard to study. Most of what they know is from studying mutant plants that may lack the capability to make a certain hormone and adding it to the plant. A good example is a dwarf plant that lacks gibberellins, and by spraying them on one, it will grow normally). Low or high temps slow the action of hormones as well. Drought conditions also influence hormones, especially abscisic acid.
Speaking of dwarf plants, this is a ficus macrocarpa “melon seed”. Not much to look at yet, needs a wiring job and another year or so. It has short internodes, dense backbudding, and doesn’t like to thicken branches or the trunk. It was grown by Erik Wigert and when I got it it was in a 3 gallon pot and was about 8 feet tall. I chopped it and put it in this pot about a year ago or so. Maybe two. It backbuds like a ficus salicaria and it’s been a struggle to keep the fungus off it and keep it green. It’s almost always yellow. I’m curious to learn if the plant is a mutant or if it was selectively bred over successive generations for its dwarf properties.
Look for a post on the above tree explaining branch placement, for different effects, soon.
So, after reading all those words (and you read them all, right?) what did we learn with all this science? Well, if you’re a reader of the blog you knew what those techniques were, but now you know the what and why of the hormonal battle going on Behind The Green Door (heeheehee) of our trees’ leaves and branches. The terms and phrases are really superficial to the causes and effects for most people who do bonsai, though it helps when you are writing a blog or giving a demo to amaze and confuse the audience with technical jargon. This is what you should take away: Defoliation, with and without growing tip pruning, has definite and measurable effects upon the plants we work with. Care must be taken as to the timing, the frequency and the health of the plant. It is a valid technique in bonsai training that works, predictably, if the above cautions are taken into consideration.
Phew, that was some deep shit there, am I right? Speaking of which, maybe I should do a fertilizer post soon……
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I’ll be making two appearances next week, one, November 5th, in Cocoa Beach, for the Brevard Bonsai’s annual Multi Club Auction (Bonsaisocietyofbrevard.com) wandering around like a fool. And in Ft Myers, as a headliner at the Bonsai Society of Southwest Florida’s Annual show, Sunday November 6th (Show Schedule). See you all there!