Apparently he wants 111 to eventually take over and make the trees vigorous. Once 111 establishes I don't see how M9 would have any influence but if you dwarf a tree until it begins to fruit often fruiting itself will keep the tree in bounds.

In most situations I wouldn't recommend allowing the more vigorous interstem to contact soil and I'm sure that's the mainstream perspective, but I'm not the authority Cummins is. I've heard him speaking at lectures of the dwarfing affect of fruiting itself, so that is something he thinks about for sure.

harvestman Ithink you have the combination backwards. The M111 is the rootstock, the G11 is the interstem.

Rob, I have some combos and also talked to Dr Cummins about it. Seems he believes by planting the interstem by half it increases the influence of the interstem. I have also read that a certain length of interstem needs to be grafted to have influence. Some think the longer the interstem piece the greaater the influence.

My mind really twisted that around, in some part of my brain I'm well aware that the interstem is always the dwarfing rootstock- ah spring. I need some sleep.

The longer the dwarf interstem the greater its influence- I've read it so often I assume it's established by research, but I don't know.

I cannot understand why you'd want it planted half in soil. It would be a trade off as far as getting the immediate anchoring of 111 as the deeper it is the less it would grow in most situations. From a horticultural standpoint it seems like a bad idea, but I think you should call up Jim. He's usually ready to discuss root stocks.

My thought is why go to the expense of an interstem and then bury it so the 111 doesn't have as much influence. Why not just plant a tree on G11.

But all I really know about interstems is they aren't popular. Almost never used commercially. There has to be a reason for that.

Wait, I think I've solved the mystery. He wants to bury all potential burr knots of the 111 as in the industry there is concern about these somewhat vulnerable areas.

I use 111 as my primary rootstock, never bury it and I've never had any problems with my burr knots on literally 1,000's of trees and scores of sites. Maybe I've been lucky. I have heard they are more a liability further south.

The following is JIm cummins respnse to my questions a few years ago,

"We strongly recommend that trees on G.11/MM.111 interstems be planted
with half the interstem G.11 exposed above permanent soil level, half
below soil. This permits the G.11 to take root and the tree to
develop a dual root system. The precocity and productivity induced by
G.11 as a rootstock should be slightly diminished. The MM.111 will
provide solid anchorage; staking will not be necessary for tree
support (although we do recommend temporary support to facilitate
building canopy).
We expect ultimate tree size to be about that attained with Malling 26
-- without the problems of fire blight, crown rot, and burrknots."

Obviously burrknots were one point he was considering.

What was unclear to me was how much if at all I was increasing the effect of the g-11 by allowing it to root.

Presumably it's rooting would be somewhat dwarfed as well and the M-111's would remain more vigorous.
In practice I know the m-111 will root up along it's length quickly, but it made for some pretty deep holes with most of the roots at the bottom, to bury a portion of interestem on both.

So, he's also burying 111 to avoid fireblight and crownrot because these are presumably not issues with g11. I'm guessing he doesn't really expect it to affect the dwarfing of the g11 one way or another-the 111 vigor would only be reduced a short while by planting deep and a less vigorous rootstock above would soon be overtaken by roots of the 111.

I've never had fire blight affect 111 either and it is resistant to crown rot but maybe not as much as g11. I would probably just ignore his advice unless I saw research that showed it advantageous in the region where I was planting the trees- but than, I'm a contrarian.

In the south, M111 is not resistant to crown rot. I've lost two
trees on M111 to crown rot, so I can understand his logic.

111 is crown rot resistant- no rootstock is crown rot immune.

Here is a link that might be useful: mm111, crown rot resistance

It is resistant to wooly apple aphid and is quite tolerant to fire blight and crown and root rots.
Tolerant is not the same thing as resistant.

Missed that- but for all practical purposes it seems to be a very narrow difference- in fact as narrow as language would allow.

Resistant doesn't mean immune either so your experience hadn't proven a lack of resistance but now we have the actual rating. Thank you for the correction- - I read what I wanted to see.

I never said it was immune, I said it wasn't resistant, and the authority that you quoted, virtually said the same thing. It's tolerant to crown rot, but not resistant to it. You may think that's a narrow interpretation, but I don't.

I've had other trees tolerate crown rot and survive, but they
could not resist it.

No, I was just unaware of the terminology rating Cornell uses and when I began my nursery, 111 was as good as any rootstock available for wet conditions. Now Cornell places its own rootstock a notch above this old workhorse and calls it resistant and 111 highly tolerant. I doubt that rating is universal in terms of specific terminology but I really don't know.

The important thing is they claim their's is better against crown rot and there's a very good chance this claim is based in research, so I'm grateful you drew me to the distinction. However, in my own climate, in a wide range of soils, 111 is not very prone to crown rot from my own experience. I would not go against sound horticultural practices and follow Jim's advice, but if I had your experience with 111 I would.

One other reason Dr. Cummins may be suggesting that planting depth is that it also discourages suckering:

Apple Rootstocks- Domoto, Iowa State
"Suckering is a problem; can be reduced by planting
interstem-rootstock graft union below ground."

I wanted to get the most dwarfing possible out of mine, so I planted them with the entire interstem and a few inches of the MM111 exposed. Of the 5 G11/MM111 interstems I planted last spring 3 have some suckering this spring. Of the other ~15 in-ground apple trees (on G11/G16/B9/G65/M27), none of the others have any suckering, except for one on G65.

But, I don't think that suckering is all that bad a problem- I just quickly pinched them off.

I wouldn't have expected it from the literature, but In terms of size, the G11/MM111 interstems have actually lagged behind the G16 and B9 which were planted at the same time (~.2" scion caliper and ~9" in height after the first season of growth). When I looked back at my records, the G11/MM111 were actually a bit smaller when they came from the nursery, so it's quite possible that they are just staying even. I'll keep an eye on it.

I also have a B9/B118 interstem, which hasn't suckered and has been more vigorous than the G11/MM111's, similar to the B9 and G16, or maybe a bit bigger.

I didn't know that Cornell had its own rootstock. What is it called?
All of the nurseries that I buy from use M111. It's the standard rootstock that's used in the south, and yes all of my apples sucker, so much so, that's it's hard to keep up with them.

I don't know much about interstem planting, mainly because
nobody offers it in the south, and I've never had a chance to use it.

The rootstocks developed by Cornell are the Geneva series. The most commonly available are the G11 and G16, which are a bit bigger than B9 and G30, which is supposed to be analogous to M7.

The most selection with these rootstocks is from Cummins Nursery, which was actually started by Jim Cummins, the developer of many of the Geneva rootstocks. I've gotten about 2/3 of my apple trees from them, as they carry a lot of selection, both in terms of variety and rootstock.

Page from Cornell describing them

Thanks for the info. Looking at the Cummins site, only a few of their apples would do well in the south.

Very little of their selection is left at this point in the season. They update their list in late summer- maybe mid to late august.

Maybe Cummins should just plant them out with both rootstocks below ground level if that's how Jim feels they function best.

I don't find suckering real time consuming to deal with if you have a good loppers and pruning saw, but it's a chore I'd rather do without.

Every time I order trees from Cummins many are crooked and all are small. I think they may sell their premium trees retail and sell there smaller stuff at wholesale prices. Not worth it for me, unfortunately. Eventually Adams and others will hopefully have the Cornell root stocks.