One of the other uses of an interstem graft is to gain compatibility. There’s an apple cultivar someone discovered was compatible with pear for instance. Graft that to a pear limb, then graft some other apple cultivar onto it. You then have a pear tree also producing apples (of your desired variety), by way of that “interstem”.
As for seedlings I’m mostly using grocery store sourced Golden Delicious. I am guessing that they’re from a large commercial orchard, probably with crabapples providing pollen. If so they’re roughly 50% crab and GD. From seed they form a taproot whereas (to my knowledge) clonally propagated rootstock like MM111 does not. Just seemed like that might have better results…
If you use Pink Lady or Granny Smith seeds, they are stored so long that you don’t need to stratify the seeds and often the seeds are already growing inside the apples and they can go straight into pots.
I do like your thinking about being half crabapple though, that’s probably the best aspect of commercial apple seeds for rootstock.
Pears tend to take a few years longer to fruit so the tree usually stouter by the time it’s loaded up with fruit. Pear roots also get those beefy roots like molars (human teeth) that probably anchor the tree better. Quince is also probably the most dwarfing and it’s only in the neighborhood of 50% versus 60-80% on the most dwarfing apple rootstocks.
edit: I should note that a Quince interstem for dwarfing is probably a bad idea. Or at least I’ve never heard of it being done and working any better than grafting Quince onto Pear usually (doesn’t) work. Probably for that reason.
I’ve heard that quince can be a free standing tree, but according to my friend’s girlfriend, who is growing cider pears, she needs to stake her dwarf trees, but she’s new to this and might be being overly cautious.
I use seedling I start myself for rootstock too. I have a question about spraying them. I have been using random apples to get seeds from and it has worked fairly well until this year. Last year I planted seeds from Jonagold and Rome Beauty the Jonagold did real well but the Rome got powdery mildew so bad that some died and the rest didn’t grow enough to use them for rootstock. This year the seeds were from yellow delicious, Fugi, Pink lady, And empire. Out of 50 seedlings started I have 2 yellow delicious and 3 Empire that might make rootstock next spring. The rest either died from Powdery Mildew, Scab, and CAR. I either have to try to spray or pick varieties that have some disease resistance. Do any of you spray your seedlings that you start for rootstock or don’t you have a disease problem. I see that some of you are useing disease prone apples.
When I spray my mature trees I also spray the seedlings in the nearby “tree nursery” area. I therefore haven’t noticed much in the way of fungal problems with them. Since ultimately they will not have any trunk/limbs/leaves above ground, I hadn’t given that much consideration. Hmm…
The Geneva Rootstock official documents say that the tree needs a “shank” for the rootstock to have a dwarfing effect. Here the thing is:
The Geneva folks say it’s ~10” for the full dwarfing/precocity effect of the rootstock from the tissue culture rootstock liners. You might need more than that in certain climates/soil/fertility/etc and less elsewhere. And there’s presumably more in-depth articles/studies/trials elsewhere.
But if you stick a 2” M.27 interstem on a seedling rootstock and were hoping for hyper-dwarfed, drought-tolerant apple “bush” you’ll probably have a surprise in your not so distant future.
Doesn’t seem like they’re talking about interstems, but the advice is likely still fairly relevant. With a stronger rootstock under the interstem piece, also seems reasonable that it would need to be a bit longer to exert (more of) the dwarfing effect.
It’s also interesting that they recommend burying the crown 4" below the soil line. I mentioned in a {social media} group that apples are capable of adventitious root formation so burying a little deep isn’t a big deal. A user essentially yelled at me to never recommend that to anyone under any circumstance. He was emphatic and threw bad language my way
I’ll keep burying 4" or so of the interstem piece, confident in the knowledge that that isn’t causing any harm. And hopeful that it’s actually helping.
The Geneva people are talking specifically about tissue culture plants, which unlike the rooted cuttings of rootstock don’t have much/any trunk below ground already, so you would only have about half as much of the dwarfing but beneath the Scion otherwise. Most of the varieties used as an interstem readily root (it’s a trait that was specifically selected for), so it’s probably not going to do any harm.
If you selected your rootstock specifically for crown gall resistance or something and your interstem lacks that them that could be a problem, but that’s usually not what people are doing. Facebook is usually pretty awful.
I didn’t actually find the post, but I think I found something better, a study from China; there’s lots of different data, but they’re looking for maximum fruiting and the recommended interstems of 1 foot (actually 30 cm but it’s basically a foot) for some dwarfing effect and maximum fruiting.
