In La Florida, we have people we like to call “snowbirds”. They’re a breed that lives in Florida for most of the year (primarily in the cooler months, hence the “snow” part) and then travel up north (the “bird” part, like an annual migration) in the hot months. Now, I’m from up north originally, and I don’t understand the concept as I can remember summers in Massachusetts being stiflingly hot and many homes don’t have air conditioning like Florida homes do, and the evenings can stay hot all night long. Here, the temps tend to drop because we, though we are tropical, have this thing called “radiational cooling”, like in a desert, meaning the heat radiates off to space at night. We can sometimes drop by 30°f. That’s like going from 35°c to 18°c, or 95°f to 65°f, especially if we have an afternoon thunderstorm.
Anyway, Wellesley is one of these snowbirds. She lives in Ft. Myers FL and goes to New Hampshire for the summer. As such, she’s left several trees in my care, two ficus and two buttonwoods (you’ve seen one of her ficus in these two posts first appearance and second appearance ). They prefer the warmth and grow best in the heat, especially the buttonwoods. This is one of them today’s victim:
I’m just starting to cut the leaves off. Aha! Defoliation. What, why, how dare I!
Well, my friends, why? We do it for reasons.
Or we should. Let’s describe what happens when we do defoliate. and we will get to the why and how as we go along.
Firstly, most people think we do it to get smaller leaves. That’s a true story. But that shouldn’t be the only theme in the story. Like I said, there are reasons, and leaf reduction is one. But not the most important reason.
Let me list some reasons:
Leaf reduction. Branch elongation. Branch ramification. Reduction of transpiration stress. Removal of diseased, damaged, or old/inefficient leaves.
Let’s work backwards and jump around hither and tither, as I like to do.
If a leaf has been damaged by insects, or disease, or is just old and inefficient, remove that leaf. There’s a point, from any of the three above reasons, where that bit of foliage (leaf, frond, needle, scale) will take more energy than it gives back to the tree. I.e., pine trees, in development, get their older or damaged needles plucked for this reason.
Remember that a plant is basically a solar panel, taking the sun’s energy and converting it to energy. In this case, carbohydrates and sugars.
For this reason, I don’t agree that cutting a leaf in half is beneficial to a trees growth, like below.
Now, doing this can help in the reduction of transpiration stress, but that’s kind of just turning off the growth hormones until the weather breaks. The tree still has green, and it won’t grow until we remove enough of that leaf to trigger an abscisic acid response, which causes new growth at the dormant bud.
On a buttonwood, I remove at least 95% of the leaf, but I reserve the two glands on the base of the leaf, just before the petiole (I discuss this in the post Jorge’s buttonwood, if you’re curious).
Branch ramification. At the junction between the petiole and the branch, we have a dormant bud that, when activated by cytokinin, will grow a new bud, and not just a new leaf but a new branch.
Hence, if we defoliate and cut the grow tip at the end of the branch, we get more branches, and we call that ramification (there are two hormones in play here: auxin and cytokinin. Auxin causes a branch to elongate, cytokinin causes dormant buds to activate. In this scenario, the auxin is the dominant hormone, and suppresses the cytokinin. Auxin collects at the grow tips. Therefore, if we defoliate but leave the tip intact at the branch end, we get branch elongation. But if we cut the tip, we remove the auxin, which makes the cytokinin dominant, causing backbudding. It’s like a computer program). Kinda like on a pine tree when we pluck needles and cut candles.
Now, today I’m repotting. Defoliation in this case helps the tree with transpiration stress (it will do all those other things we are talking about too). Transpiration is when a tree pulls water up from the roots, into the leaves, and evaporates. It does this so that photosynthesis can occur (photosynthesis takes the carbon dioxide from the air, water from the roots, and using the sunlight as the energy source, breaks the carbon dioxide and the di-hydrogen monoxide (water), and makes carbohydrate. Carbon and hydrogen. This process creates oxygen, or O2. Wow!).
Anyway, the defoliation and root reduction during a repot helps to balance that transpiration. There are times when you should not defoliate when you repot, which I will cover in an upcoming Brazilian Raintree post, so you’ll have to wait for that one.
Now, back to our tree. I’m repotting (which is a specific potting technique I discuss in this post) to get a more artistic planting position. But I know (from experience) that this tree will recover faster with a defoliation.
Here’s the pot.
An American made pot.
From Forest Inn Pottery. It’s a good pot.
The style this tree is mimicking is how a buttonwood grows naturally in the Florida Keys, twisted, gnarly.
All these bends and switchbacks are natural.
It’s hard to mimicking that in a styled tree.
Below, this was wired into place; not as dramatic.
So the idea here to pot it to show off all those features.
And, of course, I fertilize, add some prophylactic systemic insecticide for chili thrips, and add some sphagnum to the soil top, and then pre-emergent weed preventer.
This brings us to the last reason we defoliate: smaller leaves. The worst reason. It is true that we get smaller leaves when we defoliate. The reason is that a plant needs only a certain square inches of leaf surface to be efficient and to have a balance between energy needs and transpiration stress. So if we cut off all the leaves, those hormones will go crazy making new ones, and they’ll make 2-3 times the amount their tree had before. But once it reaches that harmony, the leaves stop growing larger. That’s your smaller leaf right there.
But, if we build our branches, and defoliate, prune, and cull unwanted branches, like we should be doing, and we do it seasonally and properly to the trees developmental stages (both yearly and throughout the year) we will have more branches, and, therefore, more leaves, and they will be smaller by default.
Two things to add. First, the why’s, when’s, and how’s of defoliation are different for each tree. That’s why I kept mentioning pines. And secondly, and I’ll put it in bold to make it more bold: ONLY DO THESE TECHNIQUES ON HEALTHY, GROWING TREES.
And that’s the way it is.
If you want to read more about how plant hormones guide growth, go to this post: I use some fancy words to justify my defoliation habit, go figure.