Air layer roots on both sides

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I have a couple of 2 year old rainbow eucalyptus that we nice and lush and growing out until I was gone for a few days in the heat of summer. Much of the lower growth died back revealing some branches with ugly loops. About a week or two ago, I decided that when the plants came in, I'd chop off the ugly branches and hope for some back budding. The plants would fit better in the house that way and last year I did get some minimal new branching to occur during the winter. And if they died entirely, that's fine too as I have another more lush tree the same age, and a younger crop of trees and a ton of seed as backup if needed :)

Since I was going to chop anyway, I thought I may as well try some air layers. If they work, I have some nice tops with better branching. If not, no loss...I was chopping anyway!

I didn't expect the layers to take so I didn't take pictures or note the date or anything...which is too bad. From some pictures I'm pretty sure I took that same night, I'm pretty sure I started the layers on 9/13. So roughly 10 days ago.

Today, out of curiosity, I opened them up to take a look...and one of them has roots on both sides of the layer!

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I did break the root tip before I got pictures but hopefully the pictures are good enough to see it as a root. I broke the root off completely before reapplying the sphagnum for the layer.

I've read in a couple of places that horizontal branches tend to layer better than vertical. This second layer I started is on a more vertical section.

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There is some callous and swelling and maybe the hint of some root budding, but maybe not. Definitely not as far along as the branch with the dip.

Both trees are roughly the same size. The branches are the same size. They are in the same grow bag. Sample size = 2, but otherwise about as identical a situation as one is likely to get. I will certainly try to pay more attention to vertical vs horizontal layers and the results in the future to see if these results hold.

What I find interesting is that people always talk about needing lots of growth tips to produce auxin to drive root production when layering. On the "apex" side of the dipped branch there are growth tips and leaves and a source for downward flowing auxins. There are more root tips on that side. But, there are currently no leaves at all on the trunk side of the layer. There aren't even any low branches further down the trunk that could pipe auxins up. The only "up" on the trunk side is about an inch or so of branch before it connects to the trunk.
 

0soyoung

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It is rare that the direction of the polar auxin transport can be reversed and then it is often limited to the vicinity of the root collar of species that exhibit a propensity for suckering.

At any rate, this is curious and indicates you should be able to root upside down cuttings as well as right-side up ones.
Another thing you could do is to make longer girdles so that the two edges can separately be bagged up in sphagnum (or whatever rooting media you use). Having the top of the girdle separately packaged from the bottom edge would also make the case more persuasive.

... fascinating 🤔
 
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At any rate, this is curious and indicates you should be able to root upside down cuttings as well as right-side up ones.

I've done this with willow (salix). Either end of a willow stick will root if placed somewhere humid enough.

So I guess I shouldn't be too surprised the air layer end without leaves would root...at least on some species. I haven't done thousands of layers, but I have done a fair amount and haven't seen this before on any of my other layers. I was going with the assumption the low spot on the branch had something to do with helping it along.

Since I broke the root tip opening up the layer to see what was going on, I just finished breaking it off entirely. It'll be interesting to see if it, or others, return.
 
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When I went to water these guys today, I noticed what looked like root trying to climb out of one end of the tinfoil I had wrapped around the layers. So I unwrapped them to take a look...

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Both of them had quite a few roots layering the bottom of the sphagnum.

I pretty sure I started the layers on 9/13. I am sure that on 9/23 the above pictures were taken and there were tiny roots starting. Today is less than a month and this is what I have now...on both layers I tried.

I probably should have grabbed some more sphagnum and wrapped a bigger ball to give the roots a little more room to grow for another week or two. But, I am currently out of sphagnum. So, I cut them :) I kind of rudely scratched out a couple holes for the two layers where I could in the same bag and shoved them in. I wasn't as gentle as I should have been and likely broke some roots in the process :( Maybe they'll take, maybe they won't.

What I was actually after is how strongly they would back bud...or if they would back bud at all given how much of the top I took off with the layers.

The trunk end did not grow back new roots...though callous almost looks like it might have if I left it long enough.

20201008_120213.jpg

That's it...just a status on the result of the layers for those who might be interested. I may post back one more time for completeness when it's clear if the layers will live or have died.
 
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