I don't know everything about it but I think it is species or plant size dependant. The idea behind completely girdling the branch is to remove the phloem (which carries starches etc. made by the leaves downward) and not remove the xylem (which carries water and nutrients upward.) If done correctly the branch still gets water and nutrients to grow but the starches and growth "horemones" (auxins etc.) created in the leaves get trapped at the topside of the girdle. This accumulation causes the formation of new roots. The bridge might be neccesary for a plant that does not have many branches because the roots need starches to grow and thrive, girdling stops these from getting to the lower parts.
Just some observations based on the limited knowledge I do have.
Good luck,
Turtle

Turtle,

I hadn't thought of that application for a bridge, but it makes sense. Thanks.

George

Ahhh yes, air layering. I went out and scouted an adult grove of American Beech a few weeks ago....

I'm going to be air layering an American Beech this spring. I've already selected a nice thick low branch that has some hollowing from an old inury that has healed over quite nicely. The tree itself is one that I used to climb up to the top as far back as when I was 5 years old & younger back in the early 1970's.

A local bonsai enthusiest suggested that I use the girdling method with spagnum moss & root hormone, and that American Beech is fairly easy to air layer and takes about 60 to 90 days to produce some nice fiberous roots. I'll start the air layering in mid March when we start getting warmer days.

If I am successful in air layering this wild North American Beech, it will be a challenge to dwarf the leaves, as I heard it can take a few years of careful leaf pruning.....the timing is crucial.

I've taken some pictures of the forked V-shaped branch I'm going to air layer, but don't have any URL link. I wish the bonsai gallery had the function to upload pictures instead of using links to post pics.

David in zone 5b
north east U.S.

Bridging I've read is a good alternative for slow rooting trees such as Pines which can take up to two years. In practice I've heard it's very unsucessful. Pines just don't like to airlayer. I haven't even bothered to try. Everything I've tried I've ring barked and let it go. If it made it great, if not it was free anyway and I've still got the bottom of the tree to work with. The exception is when I layer off bad grafts, which is most grafts. Those are do or die, but then again it's all fairly cheap material anyway.

You're right on about the water and nutrient's going up but the food produced being stopped on the way down. Bridging or wire tournequeting just slows it down where as complete ring barking stops it all right now. As the tree grows tourinquets eventually completely cut things off but it's a slow and long process.

If a species will root when "girdled" & the bark & cambium layers are removed all the way around, why bother with air layering at all? Why not lop off a cutting & stick it in a pot. The concept seems to lack common sense. Everything I've read about air layering indicates that by partially severing the cambium layer, it reduces the flow through the bark & forces the the branch to attempt to put out new roots in an effort to support the branch's needs.

There is a juvenality (is that a word?) factor to consider in vegetative propagation. Usually juvenile wood is more vigorous, has a greater percentage of dynamic mass and roots easier than old wood. It's probably best from an ease of propagation standpoint to use cuttings when possible if many clones are the object, but when a large plant with special carachteristics is desired as a bonsai subject, air layers offer an opportunity to develop roots on much older wood. Though cambium and phloem are severed, the xylem still moves moisture to upper parts of the layer, hopefully increasing the maximum time that the plant remains viable for root initiation when compared to cuttings. Photosynthate (sugar, starches, oils) and hormones (auxin in particular) that is being translocated downward through the phloem would normally end up in the roots. When it hits the severed phloem it concentrates in that area where the layer makes it cozy for roots and making root initiation likely.

So generally speaking, it's quite possible to layer wood that is many years old, but unlikey that you would be able to root cuttings of this age. Next you might consider the many varieties that are very difficult to propagate as cuttings. Some of the dissectum Jap maples and persimmon are first to mind, but there are many others.

Al

I've done air layering on branches, and it's great.

I have a question about trying to get some new roots to grow on a coast live oak. I'm hesitant to girdle it, as it is 2 1/2" and might die. I'm thinking of trying the slit method of air layering with sphagnum moss.

Does anyone have any comment of advice?

Hi all
George.
some of plants like rubber plants which easy to airlayer,cut half of branch and place toothpick betweem them and pace moss. that metohod may not work every plant.

normaly two year or three year old branch work well If barnch is too old,it will take long time to depelove roots and may not grow well. younger branch out perform old branch. first year, young branch smaller and thiner but within two to three years, younger branch grow biger and better than older branch.

if branch you are going to airlayer is thin, use twine tie to other branch so that airlayered branch will not brake.

Wait to leav are develloped. If airlayer before leav are fully developed, it may not make it.( also protecting from late hard frost).

If you are going to airlayer branch which has flower or fruit, remove all flower and fruit. some time reduce twig(s) will help. but have to have enought leav on branch which you are airlayering.

Before airlayer, feed tree with balanced fertilizer.
If you air layer top branch, lower branch with lots of sun do better. avoid old branch shaded branch. and water the mother tree properly.

some tree's airlayer is ready to transplant 2~3 week some takes 3 to 4 month or longer. depend on plant and weather.

most airlayering I do are remove whole bark and cunbuim 3/4 of inch. If you leave cunbium on brench, you will have very poor result.

airlayering Japnese maple may take very long time. you better off start from seeding and graft later. Forget start fron cutting.

Don't keep sphgnum moss too wet,
but also not make it too dry either. It is good time to start airlayer now.

sorry for sisspellings and bad grammer.......yama

Bushwhacker.

Girlding is absolutely different from taking a hardwood cutting. You leave the branch attached because then the leaves are recieving sustinance from the trees roots. Then the food it produces move down and STOP at the girdle, stimulating new roots. The reason it remains attached is that it is being kept alive during the process of forming new roots by the trees original roots. Taking a cutting would separate the branch from the roots while it is growing new ones - not likely to work well.

Hi,

I hope to be able to propagate American persimmon (Diospyros virginiana L.) using the technique of 'air-layering'. Despite the said difficulty (?practical impossibility) of rooting softwood/greenwood cuttings and hardwood cuttings alike, I believe that air-layering would work reliably. If it does, I'll move on to common/northern pawpaw (Asimina triloba L.).

EVIDENCE that this technique will work: I received a containerized, grafted American persimmon from a nursery and it nearly seems certain that the base of the wild American persimmon rootstock bellow the graft was buried under 3" of soil accidentally and this caused, as far as I can tell, the trunk of the rootstock to put forth fine root hairs that looked recent. Being concerned that this was girdling the sapling - that the fine root hairs would not increasingly establish and that the tree would become girdled by the soil, I removed the excess 3" of soil so that only what appears to be the original, dedicated root-system would be covered with soil.
Now, what was an ambiguous region: half root-system/half root-stock stem, is simply the root-stock's stem only.

So, I'm going to attempt to air-layer propagate one of the greenwood branches of an American persimmon tree (starting now: August; zone 6b).

I'll use a powdered rooting hormone and sphagnum moss soaked in willow water (not saturated before applying) and see what happens...

Any thoughts?

Thanks,
Steve