Trying to make sense of differences in graft vigor

General Fruit Growing
#1

I took advantage of a foggy morning to take photos of about 7 persimmon trees I grafted, one from last year (2014) and the rest from this year. I’m trying to make sense of why some grafts grew much better than others. Larger rootstocks seem to push more vigorous growth, but I’m starting to think that it also makes a big difference if grafts are placed lower on the stock and on relatively larger diameter portions of the stock. I’m thinking mainly just about persimmons here, but I suppose if my hypothesis is true it would apply broadly. The hypothesis – I don’t mean to suggest this is anything novel; for all I know, this is common knowledge that’s simply new to my thinking – is based in part on something Alan shared about pruning and considering the diameter ratio at the point of attachment and partly on Bill Reid’s advice on his fantastic pecan blog to place pecan grafts no higher than halfway up the stock (i.e. to remove at least half of the stock.) Basically, my hypothesis is that the vigor with which a graft grows is greater if more of the stock is removed and the graft is place lower on the stock, and it’s especially greater if there aren’t any significant reductions in the diameter of the stock between ground level and where the graft is placed (especially places where the stock forked or branched heavily and the continuing leader is significantly smaller than below that branching point.) I’m curious to hear if this makes sense or seems likely or jives with your experience or…

I should perhaps note a couple things that are a little different about my persimmons. First, most of my rootstocks and all of the ones in these photos are volunteer native persimmons in and around my pastures. I think it’s possible that the roots are 10 or 20 or 30 years old or more. It seems like one can mow down persimmon trees and they’ll just keep coming back year after year after year, so I have no idea how many times that happened with these trees. I mostly let them grow for 2 or 3 years (without mowing) before grafting them. Secondly, almost every one of these trees seems to get attacked by borers (I guess persimmon borers) every year (if I remember correctly, in the spring) that bore in just above ground level, sometimes up to about 5 holes (about 1/2" or more in diameter) per little tree. Sometimes it looks like the trees have been damaged so badly that they won’t survive, but they mostly seem to survive anyway. I wonder if they aren’t causing major differences in relative vigor, though.

All grafts are from this year and all are Asian, except where noted otherwise. A close-up of the graft union area follows a photo of each tree. All grafts were various forms of bark grafts.

Number 1. This one grew well. The stock was relatively large. I placed the graft at a point where the stem was still fairly large.

Number 2. This is a native on native. It grew well enough that I think it will survive but not with near the vigor of some other grafts. The stock was average size. I placed the graft rather high where the stem wasn’t much larger than my scion.

Number 3. I grafted this tree on 3 separate stems (just for back-up in case they didn’t all take or survive, but they all have so far.) All 3 grafts grew pretty well. All three grafts were placed on relatively large diameter wood.

Number 4. This is the only other native. It was grafted the lowest onto by far the largest diameter stock. I grafted on opposite sides of the stock. Both sides grew vigorously, but one side broke out before I staked it well. It didn’t branch like some of the Asians, but it had by far the most vertical growth.

Number 5. This is a hybrid. It barely leafed out but it did minimally survive/stay green for at least two or three months. It might even be barely alive now, but if it’s not dead already, I expect it to die before it leafs out next spring. I placed the grafts relatively high on the stocks.

Number 6. This is the only tree among these photos that I grafted a year earlier than the others. It has looked reasonably healthy, but it’s put on very little growth, even after two years. I placed the graft quite high, and there’s a major reduction in stem size well below the graft union.

I’ll continue below.

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#2

Continuing with number 6. Here’s a photo of the graft union followed by a close-up of the “major reduction in stem size.”

Number 7 and 8. Both of these grew well. They were both placed not-too-high on relatively larger diameter wood on average or better size stocks.

#3

I liked topwork on a larger caliper tree the best. The grafts grow real fast and faster fruits production.

Tony

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#4

To me it’s a plumbing issue. The larger the plumbing, wood diameter, at the point of graft attachment, the faster the graft can grow. Big plumbing can pump more water to the new shoots. Same thing said a different way, the tree is trying to replace the lost wood. The more taken off the faster it grows back.

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#5

Excellent information.

#6

definitely the case. Perhaps the best way to illustrate this would be to hypothetically chop down a dormant tree into a stump and grafting just one bud onto it(bark grafted). Before the tree canopy was ‘beheaded’, all the stored energy in the roots were ‘pre-assigned’ to feed all the buds of the canopy head for next spring. There already was a previous allotment, or proportional food/energy ration assigned to all or majority of those buds, but since they have been removed, all the energy from the roots have nowhere else to go but to that one bud that has been bark grafted. And surely, that bud will shoot up and grow quite vigorously

another scenario would be those sweet potatoes sitting on one’s kitchen counter that got left over from thanksgiving(the pardoned ones), and are now partly shriveled but sending out shoots from all ‘eyes’.
you could simulate a tree-stump-analogy test by gouging all the ‘eyes’ except for a single one on yam A , and then on a similarly sized yam B, you let all the ‘eyes’ sprout, the yam with just one bud will likely be more vigorous and grow faster and longer .

lower on the stock means less pressure needed to ‘pump’ or ‘push’ or ‘pull’ the sap upwards into the scion.

in analogy, there will be less risk of hemorrhage when we elevate a lacerated leg or arm, and vice-versa.

as the ubiquitous force of gravity is such a universal hindrance(heck even light gets bent by it!)

additionally, the distance any fluid needs to travel is negatively correlated to the volume flow, which means the volume of fluid delivered is decreased if the scion is farther from the source of fluid(the roots).
when i multi-graft a tree with several branches, i see to it that the rare scions get grafted low, and the less precious ones higher

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#7

I can see I have something to learn here. I have a couple of questions about the plumbing analogy (which I like and have used myself) and the location on the tree of the graft.

My logic is that no matter how large the stump the limiting factor in a well-done graft onto larger stock will be the diameter of the smallest pipe, i.e. the scion. In other words, the scion can only accept some certain amount of flow no matter how great the supply. Should I be thinking in terms of greater pressure as opposed to capillarity?

I also have to wonder how well the nutrients some lateral distance from the graft can supply the scion. That is, how much can the scion call on the far side of a cut trunk?

My other confusion has to do with the height on the tree that the scion is located. I’ve claimed (without being contradicted) that grafting higher on a tree increases the odds of a take because there is less gravity-controlled hormonal flow to suppress the graft. And in practice that seems to work out for me.

So there you have it, folks: two points to straighten me out on. Have at it!!

: -)M

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#8

Cuz,
Jerseys or Brown Swiss grazing in the foggy background?

#9

Hi Lucky,
I have all Jerseys at the moment except for one accidental Jersey-Texas Longhorn cross not in the above photo.

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#10

Mark, I appreciate your questions, but I personally feel wholly inadequate to even try to answer them, so I’m just going to add more questions to yours.

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The photo I’ve copied here is from Bill Reid’s most outstanding blog:

You can see where Bill is preparing to place a graft, and it seems to go against the plumbing theory. Holding to the plumbing theory, you’d get better vigor grafting just a few inches lower, below the branching point, where the stem is substantially larger. But perhaps, in this case, both stems are more than big enough, such that even reduced nourishment to the graft will still be more than enough and other factors – he discusses the thickness of the bark – can trump the plumbing theory.

I know that I’ve frequently done something similar to what Bill did in this photo but on a smaller scale in order to achieve what looked to me like a tidier fit with possibly a larger area of cambium contact by grafting onto wood not much larger than my scion, even when I could have cut the stock off just 6 or 8" lower and grafted onto significantly larger wood below a branching point. I’m inclined to believe now that that’s a mistake, at least when the smaller wood isn’t already as large as in Bill’s photo above. Here’s a quote from Bill that relates to this idea:
“I was out in the field grafting more Kanza trees and came across a tree too large for a 3-flap graft but too small for a bark graft (photo at right). Sure, I could have placed a 3-flap graft up near the top of the tree. But, to make sure my graft will get a good push from the root system, I like to remove at least one-half of the top when choosing a spot to graft.”

And to add to the question of how high to place a graft (aside from questions of branching and constrictions of the flow of nourishment from the roots), here’s something Bill says about grafting a tree in which he left nurse branches:
“Although chopped back to one half its original height, the central leader still holds a prominent position in this tree’s architecture. Leaving 18 inches of central leader above lower branches will help draw energy and nutrients toward the new graft and increase the chances for graft success.Although chopped back to one half its original height, the central leader still holds a prominent position in this tree’s architecture. Leaving 18 inches of central leader above lower branches will help draw energy and nutrients toward the new graft and increase the chances for graft success.”

#11

Cousin- Great info. I grafted the top of a friend’s ten foot tall Rome apple. I figured apical dominance insured vigorous graft growth. Nope. They grew a few inches and stopped.

If I graft over a low limb on this Rome next year do I need to remove other nearby limbs that might out-compete the graft? Or does the low-ness of the graft make other limb competition less an issue?

#12

That makes some sense to me. I need to remember that most of my experience (especially as pertains to the successes) is topworking on vigorous trees.

I went to Reid’s blogs (thanks for the link, by the way) and agree with you- they’re outstanding.

#13

Steve, I think this post of Reid’s speaks most directly to your question. It’s one of the blog posts from which I already quoted above:

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#14

To add-on to your post Cousinfloyd, I found that when grafting to a lower branch on an existing tree it can be useful to score the bark on the trunk of the tree directly above the branch to which you are grafting if you find that the graft is not taking (or just as a precaution to help it take). This is done by nocking a strip of bark about 1/8" wide clear down to the wood. Make the cut overhang the branch. I make the total cut about twice the diameter of the branch. The idea is that the nock cuts the supply lines that the auxin flows down to suppress the growth of lower branches.**

I have done this with grafts that healed over the year before and wouldn’t pop until I made the cut.

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#15

the bigger the stump, the larger the food supply from the rootstock becomes in proportion to the few buds one might be barkgrafting , relative to the size of the bark-grafted scion, because that stump was supposed to channel nutrients to a much larger number of buds. So even though it is true that the smallest pipe( the scion) is the limiting factor to flow, that lone scion is feeding off the nutrients which was supposed to feed all the other buds of the huge canopy which was once attached to the stump. So growth of that graft will be more vigorous.

it is hard to say if pressure actually increases , because nobody in the scientific community could explain exactly how sap rises. It is still a great mystery. The only thing that ‘increases’ pressure, is to get the soil as moist as possible without drowning the roots.

apical dominance is definitely a confounding factor. Per hormonal science, it will have an inhibiting influence on buds beneath it, but per hydraulic science’ standpoint, it is physically disadvantageous.

my take on this is that it is probably length-dependent, or a bit of relativity. Say, if an apically dominant stem(main trunk)was cut, and if the segment removed and discarded happened to be 6 " long, whereas the new scionwood intended to replace the 6-incher is of the same caliper, BUT length is 12" long, this will not fare as well as a lower non-dominant branch which was originally 2 feet long, but was chopped down to a 1" stub, and grafted over with a 2" scionwood.
this is because the apically dominant was proportionally allotted a pre-set ration of nutrients for the original 6" segment, and is now ‘servicing’ a longer segment, whereas the lower, non-dominant branch was originally supposed to ‘service’ a longer branch with many buds to feed, but is now servicing a very short one with just one bud to feed.

even if some hormonal effects ‘try’ to ‘hinder’ the graft on the lower rung, the lower rung is still having such a logistical surplus in favor of that one bud it is nurturing, because originally it was designed to nurture a much longer segment, and the fact that that longer segment already reached that size indicates the hormonal effects of the original apex have already been overcome.

now, if we should take your supposition to the extreme, we should note that the inhibiting effects of apical dominance only applies to younger trees, as apical dominance does not last forever, especially when a tree has matured and its vertical growth has slowed and instead starts devoting its energy to lateral branches to form a bigger canopy.
Grafting budwood at the topmost branches of a 300 ft tall eucalyptus tree will probably not grow as much as grafting one at the lower rungs

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#16

I appreciate all the time and thought you put into your response, and am going to have to take some time to digest it all, and to try to connect the dots.

Sometimes the science isn’t perfectly clear, or perhaps seems to contradict itself, but we end up doing what works and trying to cipher out the whys later. My brother is a working blacksmith in ornamental iron and has sometimes ended up a rigorous, good explanation with “and sometimes it’s just magic and you have to go with that”.

Thanks.

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#17

you asked, so i tried :slight_smile:
kidding aside, my input is, of course, wide open for further critique to ‘straighten me out on’ too, as we’re all trying to learn here, whilst sharing what we know

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#18

Ya, and ya done good, too.

:smile:Backatcha

#19

lol

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#20

One other wrench in the mix here is how persimmons can do plain weird things at graft unions. I have had many varieties runt out badly, in spite of the stock being ultra-vigorous. My theory is some virginiana stocks are more compatible than others for grafting. I have one graft that must be 6-7 years old and it is still shorter than I am after that many years of growth. The stem was 4-5 years old when I topworked it and it had tons of vigor. It took me three years to get any scions at all to stick to it. That is an extreme case but I have some others that seem to be less extreme versions of that phenomenon.

For non-persimmon grafts I find the correlation is much more based on vigor of stock. I have not noticed any height difference; higher has the advantage of extreme apical dominance.

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