"Reverse" thread grafting a juniper?

[leatherback]

my experience with junipers is that they have a thicker cambium layer as well

How do you come to this conclusion?
I myself have not come across any information that would cause to believe this is the case.

 

[leatherback]

I intend on using thicker branches

The thicker the branch, the bigger the scar will be though..

 

[Shibui]

Thread grafting works because both parts still have roots to keep them alive. Even if the cambium is not aligned both remain alive and grow. Sooner or later the developing callus of one comes in contact with the other and begins to unite. Grafting can take from a few months to a few years. Way too long for a scion graft to stay healthy.

For the peg graft to work you will need to align the cambium of both close enough that it will unite before the scion dehydrates. I've had conifer cuttings stay healthy for several years without roots so maybe that is a characteristic that will help this method.

I intend on using thicker branches, so a double cut may be more appropriate.

Thicker scions are much more difficult to make clean cuts on. I don't think older wood has thicker cambium. It may look that way when you cut through at an angle but cambium is cambium no matter where it is on the tree. Thicker scions will probably also have a larger reserve of nutrient and energy. Thicker cuttings can stay alive for longer so maybe thicker scions can stay alive longer waiting to unite?

When I do this kind of graft, is the non-perforated buddy tape enough to preserve moisture, or would the graft take more successfully using perforated tape and a sealed bag of sphagnum around it?

Grafting tape seals the graft to preserve the cambium and developing callus. It also holds the parts together while healing takes place so a bit of sealing and a bit of pressure. Sphagnum may help maintain moisture but usually a well taped graft will be OK. The biggest enemy of grafts is the scion dehydrating before there's a bridge to the root stock to get water and nutrients. That's where the bags come in. Bags maintain high humidity around the foliage so they don't transpire the limited moisture reserves. Misting may perform the same function but beware of filling the graft with water. Some practitioners use 'mummy graft' for evergreens where the entire scion is wrapped in parafilm to reduce dehydration until growth occurs. Probably not suited to the larger scions mentioned here.

Good luck with the trials. Please keep records ad update here so we can also learn.

 

[circledisk]

Thank you Shibui, that was very helpful. I’ve never grafted junipers (just deciduous) so I’ll use this as a reference.

The scar will definitely be larger but I imagine it could be worked on well enough. I’ll be starting the grafts soon, it may be too late here but I’ll give it a shot anyway, with a bagged branch.

I imagine the thicker scions will be able to stay alive longer. I’ll probably add secondary support somewhere to keep the heavier scion in contact. I’ll be sure to post pictures here and report back on my results.

I may also just prune the trees back first this season since these landscape trees are overgrown, and then attempt a graft in 10-11 months. We had some cold periods here in NC and a late spring, the weather didn’t really turn for collecting or heavy work until a few weeks ago. My hornbeams are just starting to bud out now, while other deciduous trees only hit the end of their first flush recently.

 

[circledisk]

Regarding pruning and grafting at the same time, there was a post I read last night with some insight. The consensus seems to be to only reduce apical growth so that the tree sends auxin back down the trunk, hopefully to the graft.

 

[circledisk]

Grafting tape seals the graft to preserve the cambium and developing callus. It also holds the parts together while healing takes place so a bit of sealing and a bit of pressure.

Has anyone ever used rooting hormone or something similar to encourage the bridging and callous development?

 

[Bonsai Nut]

Grafting tape seals the graft to preserve the cambium and developing callus. It also holds the parts together while healing takes place so a bit of sealing and a bit of pressure. Sphagnum may help maintain moisture but usually a well taped graft will be OK. The biggest enemy of grafts is the scion dehydrating before there's a bridge to the root stock to get water and nutrients. That's where the bags come in. Bags maintain high humidity around the foliage so they don't transpire the limited moisture reserves. Misting may perform the same function but beware of filling the graft with water. Some practitioners use 'mummy graft' for evergreens where the entire scion is wrapped in parafilm to reduce dehydration until growth occurs. Probably not suited to the larger scions mentioned here.

I wanted to quote this because I was about to type the exact same thing.

It is important to understand the process from a horticultural perspective first - then chose the proper tools to accomplish it. You are trying to do two things (1) hold the scion perfectly and securely in place with a tight bond and (2) prevent the scion foliage from drying out. There is no purpose to applying moss to a graft junction, and you might even slow the healing process or introduce fungus to your wound site. You would be better off adding moss to your foliage bag - as long as you could arrange it in such a way that the moss doesn't remain saturated and no foliage sits directly in/on the moss.

 

[Bonsai Nut]

Has anyone ever used rooting hormone or something similar to encourage the bridging and callous development?

The vascular cambium layer will automatically generate callous cells at any wound site. You would prefer to have auxin/cytokinin growth hormones balanced rather than elevated auxin levels from application of rooting hormone.

It is important to note that, unlike in the case of an air-layer, you are not interrupting the flow of hormones at the wound site. Auxin and cytokinin will continue to flow all around the wound site - via the undamaged tissue on the branch/trunk where you are applying your graft.

 

[circledisk]

The vascular cambium layer will automatically generate callous cells at any wound site. You would prefer to have auxin/cytokinin growth hormones balanced rather than elevated auxin levels from application of rooting hormone.

It is important to note that, unlike in the case of an air-layer, you are not interrupting the flow of hormones at the wound site. Auxin and cytokinin will continue to flow all around the wound site - via the undamaged tissue on the branch/trunk where you are applying your graft.

Wouldn't auxin levels naturally elevate to some extent at the injury site over time though? My thought about using a hormone to stimulate auxin early on, is that in a more mature branch and very mature trunk, auxin levels will be considerably lower than in new apical growth. If we avoid pruning or severe reduction in new growth, available auxin could (?) have a harder time relocating to the wound site.

We don't seem to fully understand auxin from a scientific perspective yet, but given that it sort of controls every process in the plant, specifically stimulating IAA with a rooting hormone, which controls cell division, cell expansion, and cell differentiation, could (?) lead to faster healing at the graft site.

Q&A: Auxin: the plant molecule that influences almost anything - BMC Biology

Auxin is an essential molecule that controls almost every aspect of plant development. Although the core signaling components that control auxin response are well characterized, the precise mechanisms enabling specific responses are not yet fully understood. Considering the significance of auxin...

bmcbiol.biomedcentral.com

 

[bwaynef]

I think you'd be best served with the whip-and-tongue that was pictured above (on the last page I think) and approach grafts.

 

[circledisk]

I think you'd be best served with the whip-and-tongue that was pictured above (on the last page I think) and approach grafts.

Yes that’s my thought as well. When (if) I get permission to work on it I’ll try it out