Some tricks I’ve learned about air-layering

It’s May, which means it’s air-layering time for me here in Florida.
I have quite a workload of air-layers lined up this month but I thought I’d share some tips I’ve learned along the way.
One of the easiest trees to air layer is an elm.
Therefore, today’s subject is an American elm.
For all you plant nerds out there, yes, I did say “American elm”.
Ulmus Americana to be precise.
For some reason, the beetle that transmits Dutch elm disease just has not made it to Central Florida yet.
We have an enclave of wild American elms here that are still growing strong.
Doing the research for this tree, I learned something interesting; I’d always been told the the variety of American elm we have here is called the Florida elm, or ulmus Americana “floridana”.
There is no such recognized variety.
In fact, there are no varieties of the American elm.
Now, there are hybrids (a cross between two types of plants) but, genetically, the tree that grows in Ontario, Canada is the same as the one that grows in Orlando, Florida.
Neat, huh?
Another odd thing about the American elm:
Most deciduous trees are triggered into dormancy by the shortening day and the lack of light that that entails (most people think it’s the cold but it’s not…trust me).
The American elm doesn’t respond to this low light trigger and won’t lose it’s leaves until the first frost burns them.
Weird…but true.
Anyway, here’s the tree and I’m all ready with my serial killer gloves.

The reason for the gloves (besides the obvious joke about serial killers, which will never get old) is that sphagnum moss sometimes has a fungus that, if it gets into your body, could cause a serious infection that requires months of expensive treatments to rid yourself of.
I use the regular sphagnum moss from the Midwest (I’m a poor man) but if you are concerned about the fungus, you can buy the special Chilean sphagnum that is free of it. It’s called “premium orchid moss”.
But I’m just a common man, I drive a common van, and I can’t afford that moss.
When I collected the tree I left it taller than most will recommend.

And there’s even a bit of reverse taper.

These two facts: too tall and reverse taper make this tree perfect for an air layer.
Which was my plan all along.
I’m a clever lad.
Sometimes, when I walk through doors, my ears scrape on the door jamb, my head is so big.
The perfect spot for the airlayer?
Right at the reverse (obverse) taper spot.

See, I told you I was a clever lad.
The last time I tried to airlayer an elm this large the damn thing healed over.
Yeah, really.
Imagine my surprise.
This time I’m going to make sure.
First step:
Ring cut the bark down to the wood, what is generally know as the sap wood.

Or, to be scientifically pompous, it is known as the secondary xylem.
Just to satisfy those so inclined, let’s break down the layers of the tree.
From the middle out-
The pith or medulla.
The primary xylem or heartwood.
Secondary xylem or sapwood.
Vascular cambium.
Secondary phloem.
Primary phloem.
Cortex.
Cork cambium.
Epidermis. Which is the bark.
We want to get down to the secondary xylem layer or sapwood.
How can this wanton removal of the outer layers of a tree not kill the tree?
This is the mechanisms and how a tree works, simplified:
You have two areas, the roots and leaves and, in between, a stalk or trunk.
The trunk is the pipeline between the two areas.
The leaves make food from the process of photosynthesis.
The roots collect water from the soil.
The trunk moves the food down and the water up.
Each layer has it’s own job in these processes and, when air layering, it is those processes that we are exploiting to induce root growth.
The secondary xylem is the path that the water the roots travels upward to the leaves. Hence the name “sapwood”.
The phloem is the path that the food travels down.
As long as the sapwood is intact when we remove the first six layers and the tree is getting water, the top won’t die, and when we interrupt the phloem, stopping the food from reaching the roots, the tree responds by growing new roots at the cut end.
Got that?
Let me illustrate.

Usually the advice is to make the ring cuts about the same distance away as the branch or trunk we are trying to layer.
In this case I’m making that interval bigger, because of my experience with the cut healing.
Using a sharp knife, start to peel away the layers.

In my research for this piece I get a laugh at how easy all the other authors try to make the removal of the layers to the xylem look.
There’s one picture when the bark is whole, one where they’ve scored it, and a third where it’s the sapwood is clean and pretty.
It’s not always that easy, so take heart and don’t think that your knife skills are lacking.
Just be thorough and you’ll be successful.
This looks like the sapwood.

Slow and steady, damn this elm bark is thicker than it looks.

Almost done.
One technique is to simply scrape down the the wood.
You’ll know give reached the wood layer when you’ve, well, gotten to the wood.
Don’t worry about scratching the sapwood, it’s thick enough that you won’t impede the water flow unless you take an axe to it.
One last bit about the layers.
Remember the inner or vascular cambium?
Remove that, which in our case, has turned a nice orange for us to better see it.

Nice and clean.

Now for the sphagnum.
I’ve soaked it in water to get all the fibers totally saturated.
I prefer to use aluminum, shiny side out, to hold the sphagnum in place.

The reasons being: first, it conforms to the sphagnum without a need for extra tying and, secondly, it reflects the sun and keeps the sphagnum at a more ideal temperature (below 90f).
In Florida that’s important.
Be very careful to make sure that your moss is touching the correct area on the ring cut; mainly the top.

And make sure you use enough moss.
If you’re in doubt, add more.
Don’t be cheap now, pile it on thick

And even though I don’t need to, I tie the the bottom tightly with wire.

But only loosely on top.

And you’ll notice that I formed the aluminum into a cone shape.
This is so that every time I water, I can spray some into the top to make sure the moss stays moist.
That trick is worth at least a dollar.
Please remit payment by mail to the address at the bottom of the screen, plus a separate shipping and handling charge of $9.95.
But wait!
I can repeat the same trick on a fortune cookie sized laminated sheet for free, just remit a second shipping and handling charge.
*results may vary, and actual product may differ from the advertised image*
Now just a few housekeeping details to take care of.
There is always a question of what to do with the top growth.
To trim or not.
I do trim the top branches of the airlayer.

The reason: cutting the top will stimulate new growth, new growth means new roots, and we are trying to grow roots, right?
Next, fertilize the bottom.

Errr… Weed the bottom and fertilize heavily. I use Milorganite.

And lastly, water well.
My friend Allen Carver of Jupiter Bonsai says that the magic number for good root development is six weeks.
Which should mean that I can remove this by the end of June.
Remind me if I forget to update this post.
I’m anxious to see how it turns out too.