Ok, I just air layered half of my trees. Now what. (boxwood, elm, trident maple)

Kinda just kidding, but kinda serious. I was initially just going to air layer my boxwood, which had nasty inverse taper at the base. But then something took over my brain and I ended up air layering 2 other trees whose bases I resented daily: one of those mass-produced chinese elms and a trident maple with a very lopsided nebari.

I followed the technique as prescribed by Ryan at Mirai. I made the cuts as clean as I could (using a boxcutter with new blades), scraped away more bark than I felt comfortable, tightened a large wire around the top of the layer, and filled the container with fresh akadama+pumice+lava soil, letting it dry for about a day before watering.

What Ryan didn’t explain was what care looks like after that.

  1. I assume I water the air layer reservoir throughly whenever the main pot needs watering?

  2. Do I fertilize the top container? bottom? both? neither?

  3. Should I hold off on any more pruning this season?

  4. Should I check after a few months, or just wait until next February?

  5. What is the optimal relationship of root conditions & foliage growth before deciding to air layer? (I didn’t really think this through before just jumping way into the deep end).

  • The boxwood was freshly repotted by someone else this spring and has been growing decently strong. I don’t know that it’s vigorous, but it looked healthy enough, and the base was driving me nuts.

  • The elm had a modest root system in plain soil when I bought it last year, so was repotted this spring and has been growing what I consider to be vigorously. Also hated the tube-like trunk and lack of nebari.

  • The maple had been growing vigorously. I partially defoliated it after the first flush hardened and it has responded pretty well. I realized in May that the maple was potbound, so I slipped it into a bigger container, planning to repot it next year. It had a good-ish nebari on one side, but a negative nebari on the other. See photos. I could have approach-grafted to fix that, but as noted above, I got a little air-layer-happy and just went for it.

Here’s what they look like now:

The pots may seem large, but again, I basically just followed Ryan’s lead here in making sure the top of the layer was around the middle of the reservoir.

Here’s the elm layer:

Here’s the maple layer:
00100lrPORTRAIT_00100_BURST20200618172548813_COVER 00100lrPORTRAIT_00100_BURST20200618172608683_COVER

You can see the weird missing half of nebari in those photos. The second photo shows how I actually layered off some of the nebari. Was that a reasonable approach? Was that layer large enough? (I guess we’ll find out, huh?)

I didn’t get a photo of the boxwood air layer, but here’s a photo of what I was trying to fix and the angle I was aiming for:


Any thoughts on the quality of my very amateur judgement or on what I’ve gotten myself into?


The method is basically the combination of tourniquet wire and cambium removal recommended by many Bonsai growers. Works well in a very well maintained environment. Has some downfalls if care is intermittent!

  1. Yes, and keep a closer eye on the top air layer pot as it will dry out faster than the main pot. I would suggest some sphagnum moss on the surface of the air layer pot.
  2. Do not fertilize the top, fertilize the bottom lightly. suggest a diluted fertilizer lower number. Liquid fish fertilizer would be a good choice.
  3. Hold off on the pruning, you are relying on photosynthesis to supply the energy for root formation, pruning apical tips will defeat that purpose by removing auxin when needed the most.
  4. This seems a bit late in the year for air layers to me I usually start in April/May. I would definitely wait until next year to check. Also I would protect from freezing this winter.
  5. Vigorous growth top and bottom is best. Not recently repotted or recently pruned/ wired. It also helps if care is taken to strengthen the tree with fertilizer in preparation for air layer. Essentially getting the tree in tip top shape ahead of time. Usually the prior growing season.

I would also suggest that it is wise to plan the base cut at the angle and location you desiire the roots to form.

Wishing you success and hope this extra information is helpful.


Frank’s advice is spot on. One thing I notice in the photos is that you may not have cut all the way down to the cambium at the top of the layer (I’m seeing the slightly darker color, particularly on the maple).

Am also surprised there was not root hormone. I’ve used both powder and liquid but usually use powder along the top margin of the cut before placing the moss and/or soil.

Figuring out when to separate the layer is relatively easy in that you don’t make the cut until you see enough roots to keep the tree healthy (the more the better). The faster the tree grows between now and then, the faster the roots will develop.

Am looking forward to seeing how the layers develop!

Thanks for all the guidance!

For geo-context, I’m in San Francisco, so no real chance of freezing or even high summer heat.

I made the top cuts at the angle that I plan to re-pot at, and I also actually removed that smooth transition of the cambium on the maple after taking the photo. That was my main worry, that I wasn’t taking off quite enough.

@bonsaitonight Since I just did this yesterday, would it be worth it to remove some soil, apply a rooting hormone, and then recover it?

Good question about the hormone. It’s not too late if you re-cut right along the upper margin all the way around.

If you’re really bold you could apply hormone on just half of the trunk to see if it makes a difference, but I’d save that test for younger material.

Some species may not need the hormone, but I don’t know which those would be so I’ve always used it.

update, 3 months later.

The boxwood airlayer has taken quite well, with roots in every direction. Hooray!

… and I should have just stopped there.

The Chinese Elm looks like it just laughed it off because it appears that cambium/bark has formed around the entire removed area.

I’ve taken the airlayer container off because it just made it harder to keep watered. Should I re-cover it as a precaution?

The Trident not only didn’t take, it got really pissed. Half the leaves turned red and fell off within a month!

It appears to have found 1 or 2 paths back through, so I’ve gone ahead and re-covered it with the airlayer container and soil, but is there any use to that or should I remove that one as well? Again, easier to keep properly watered without it.

Just to confirm, is there any point in re-scarring & applying hormone at this time of year? Should I just wait until next February?

One more question, is there any validity in adding some root hormone to an occasional watering for an air-layer?

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As long as there’s callus, you’re off to a good start. It looks like not enough material was removed in these photos which gives you a clue of what to do differently next time.

I don’t know if it makes any sense to re-open the cut now, but it’s a good way to learn! That said, I’d play it safe and wait until the trees start growing in spring before re-opening the cuts. In the meantime, you can replace the moss and maybe make some small cuts (i.e. re-open a small area) to see if anything develops over winter.