Air layer a graft union

Here is a technical question for the experienced IBC folks:

If I choose to air-layer a black pine at the graft union (right at the swelling; above the inverse taper), will any roots grow?

Thanks.

Sure. If you are above the graft, you will get whatever was grafter to the stock. If below, the stock.

Definitely possible. I would start the project in spring, not autumn. Don't candle prune the year you start the air layer, as making the air layer is a stress. I have had moderate success air layering JBP. My success rate is running about 70% out of 10 attempts. It is not a 100% sure thing. So there is a risk you could loose the entire tree air layering at or just above the graft point.

One suggestion would be instead of completely girdling the trunk, instead remove vertical strips of bark, down to the cambium. Make the strips at least 1/4 inch wide. Leave at least 30% to 50% of the original bark intact. Then use a pot with the bottom removed, split then placed around the trunk. Fill with the same potting mix as the rest of the pot, then leave it alone for at least one, better would be 2 growing seasons. If the tree continues to grow vigorously you can continue training the top, but if it slows down, which is most likely, then leave the foliage training for the 3rd season. When you repot, check to see if roots formed. If they did you can cut off the top and pot it up. This will lessen your chances of loosing the tree entirely. It won't form as nice a ring of roots, you may have gaps in the nebari, but you will have a higher probability of keeping the whole tree alive. The older the trunk the lower the chances of roots forming. If the vertical slots heal without forming roots, you will just have to try again. Make sure you remove all the cambium in the vertical slots, just as you would do for ring style air layer. If the tree is younger, say the graft was done less than 10 years ago, the ring technique should work well enough to take the chance.

When you don't candle prune, don't remove 2 year or older needles. Leave them, you may need them in the future. Only remove needles that brown off and die. The adventitious buds at the base of a candle remain viable for several, 2, 3 or more years. So when the air layered tree has been removed from the parent stock, after it begins to grow vigorously and gives you a big full flushed of candle growth in spring, you can then go back and candle prune, and branch prune back through several years old growth. You can cut back as far as you have needles on a branch. If you cut back to the point where there are no needles, the branch will die. So if you removed all the previous year's needles, you won't be able to cut branches back beyond the most recent year's extension, but if you kept the older needles, you can cut back into branches that are several years old. So when you know you will not be candle pruning because of repotting with major root work or air layering or other stressful techniques applied to the tree, keep the old needles so you can cut back further once the tree is healthy and vigorous again. This also holds for young material that has not been styled yet, keep old needles so that when you do style the tree for the first time, you have the option of cutting back further than just the previous years growth.

Right now I have a P. thunbergi 'Aka me' that I used this technique on, vertical slots, I set it up in June. Next year or maybe 2016 I'll be able to report back. Growth was abruptly slowed, but not stopped when I did this, so far, so good.

Using a rooting hormone is optional. I have not had any better success with using a hormone than without using a hormone. Though I have not done a significant number of air layers, so whether or not you use one is up to you. There are articles that warn that too much hormone applied can actually prevent roots, so if you do use one, read the directions and don't over do it. Make sure it is one that is listed for hardwood cuttings, not one listed for only herbaceous plants.

Why is the jbp grafted? Is it a uncommon variety? Corkbark?

Grafting is the 'quickest' way to create genetically identical trees, to make more of a select named cultivar. So with JBP if you have a tree with exceptionally short needles, or one with cork bark, the only reliable way to get those characteristic exactly like the source plant is to graft it onto the roots of another. With cork bark pines, the graft needs to be very low, down into the root system of the under stock, if it is higher, you will get a zone of reverse taper, were the understock does not display the cork bark and the trunk of the scion does form the cork bark. Using grafting, one bushy specimen tree used as the scion wood source, can be used to make hundreds of grafted copies ready for sale in less than 5 years. The Buchholz nursery recently posted in their blog that they produced over 50,000 grafted pines in the last 25 years. And pines are only one part of the Buchholz nursery product line. Grafting allows one to propagate a cultivar in quantity, wholesale commercial quantity if one so desires. (the modern use of the term 'cultivar' and the term 'clone' are largely interchangeable - all plants of a cultivar are genetically identical, as with a clone.)

Seed will always give some variation. Cork Bark JBP from seed are hit or miss. Some do come true from seed. Pines are pollinated by wind blown pollen. If the source seed had no 'regular' normal type JBP in vicinity close enough to pollinate the Cork Bark JBP 'mother plant' maybe half the seedlings will show cork bark as they develop. If any normal type pollen is in the wind, the percentage of cork bark seedlings from seed off a cork bark JBP can drop to near zero. So seed production of the cork bark trait is not reliable. Raising large numbers of seedlings can result in some new and very good examples, but the exceptionally good ones will be few in number, perhaps less than one in a hundred. It will also take 10 to 20 years from seed to fully characterize a cork bark pine's ability to produce the cork bark. Some clones like 'Kyokko Yatsubusa' will begin showing the start of cork formation as young as 4 years, with nice cork wings forming before it reaches 10 year old. (this I know from experience and Brian van Fleet's article) A cultivar like 'Hachi Gen' will not show the beginning of cork bark until it is twice that age, more than 5 to begin to show, and the branches won't fully cork until somewhere around 20 years old. (mine has not even begun to cork yet, BvF's article suggests the 20 years).

Producing JBP by cuttings, a method used with many deciduous trees, is difficult. Reliable results only happen when professional techniques are used, heated bed, mist or fog system that hourly mists the cuttings. Tight temperature controls, etc. There are a very few cultivars of JBP that will root from cuttings more easily than the normal type, but none of them are reliable to root from cuttings. Even in a professional set up, 20 to 30 % of the cuttings taking root would be considered good. Just sticking a cutting in a pot in the back yard might be successful maybe 0.5% of the time. Not a reliable method.  

Air layering - this can and does work, with JBP, a 70% success rate would be considered good, and good enough that it is worth the effort to do if you would like to propagate a plant with special, choice growth traits. It is not used commercially, because even with a big bushy stock plant, you can only do a few per season. It is a great technique for the 'collector', where one or two is all you need.

Meristematic tissue micropropagation, commonly call 'cloning' is done in a laboratory under sterile conditions. A piece of meristematic tissue is removed from the select cultivar one wants to propagate, the tissue sample is surface sterilized to get rid of yeasts, bacteria and fungi that would contaminate subsequent cultures and then is cultured under sterile conditions with nutrient broths treated with hormones to induce the tissue to form embryonic cell clumps of callus. Then under sterile conditions these lumps of callus are sub-divided, cultured and sub-divided again until enough pieces exist to meet the quantity requested in the order (in a commercial lab). Then the callus pieces are plated out on growing media and with hormone treatment are encourage to differentiate into little plants. This technique works very well for herbaceous plants, many of your box store orchids and other plants were produced this way. It is possible to produce 10,000 or 100,000 exact copies of a plant at a time. The problem is the time required is about the same as raising a species from seed once the plantlet come out of the lab. So to get a pine to the 5 year old seedling size, it will take 2 to 3 years of lab time plus 5 years to get it to size up. The problem with tissue culture of pines is that the resin of pines contains many compounds that prove to make tissue culture difficult if not impossible. Callus has been made in the lab, all articles I've read so far show major obstacles in reliably getting callus to revert and differentiate back into plants. Eventually someone will sort it out, but so far there is no economically viable way to tissue culture a specific cultivar (clone) of pine. So this if currently off the table. It is not possible yet to "clone" a cork bark JBP.

So this is why grafting is the method of choice to reproduce a specific named cultivar of pine. It also holds true for a number of other genera of conifers and some deciduous trees too.

With Japanese White Pine, clones with short needles and good blue color are grafted onto various understocks to make more blue needled JWP. In addition, in more southern climates JWP roots are not very heat tolerant. Similarly JWP roots do not tolerate being overly wet. So for southern climates JWP does better, grows faster on JBP roots, for northern climates, JWP tolerates cold wet northeastern USA winters better if grafted on P. strobus, or P. nigra. Often P. sylvestris and P. nigra are used as a general all purpose under stock. So grafting is used with JWP to give better tolerance of climate extremes, beyond just grafting to reproduce a named selected for appearance cultivar.

Can you tell I was thinking about writing an article?