AusBonsai

I'm reading that early spring is the best time to air layer most trees, including junipers. Given that shimpaku junipers produce roots very quickly (I've had an air layer produce roots in approx 3.5 months), has anyone tried doing an air layer in summer and leaving it on there all the way till winter? Any thoughts on this???

My thinking was that come winter, I can remove the air layer and repot during the dormant period. Would this work?

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Everything depends on the size of the trunk/branch you are trying to air layer of course, but generally the proposition is sound. I would leave the layer on until very early September and then cut and pot.
Good luck.

I am not sure about Shimpaku but I have airlayered juniper and left it on over winter with no problems . I think you are better leaving it on longer than taking it off to early without having a good root system . My layers seem to take longer for me than what I have heard of other peoples experiences , maybe because my growing period temperatures fluctuate so much .

I did some layers on shimpaku a few weeks ago. If all goes well I will take them off by the end of summer. If there's not enough roots they can stay in place until spring.
I also recently separated a couple of last years layers. One of those had only 2 small roots but is still growing well.
I have had many poorly rooted layers thrive after removal. I think the separation makes them concentrate on producing new roots. Even a few small roots is a step up from a bare cutting and we often use cuttings to propagate successfully so I no longer fear removing layers with fewer roots.

For me a good root system has roots all the way round . If it only has roots on one side from my experience it won’t develop roots on the other side once removed . I have a few trees which have had this happen to them and it’s harder to fix . Now if they develop like that I prune the roots off and leave it on longer .
An example of what I mean is this Leptospermum . It only had roots on the one side and you can see where the trunk has died off because of it . With this tree I don’t mind to much ,it’s part of the character but it did limit me to what I could do with it .