As Alder says, rootstocks are often chosen because they are good in the ground for various reasons, not for the quality of their fruit.
I don't understand apple genetics very well,
but I understand that if you take rootstock cuttings you're getting a clone of whatever it is-most likely a crab apple.
Whereas if you grow from seed, you have the benefits of the apple's amazing genetic diversity
and a taproot
Something I've always been told is to twist off suckers/water shoots if possible: it disrupts something to do with the growth hormones.
If you just prune it off, the tree will often send out several shoots in the same place.
That only works if you get them when they're small. The ones in your pics look too large for that.
Where are you?
If the trees are going into dormancy I'd suggest waiting and summer pruning out the suckers.
If you winter prune them, it tends to stimulate the tree to grow more in spring.
That's my experience, any tree people's thoughts?
I'm a little concerned with the aggressiveness of the rootstock in your pics as they look to be draining the energy from the rest of the tree. Definitely keep them cut back and chop and drop them around the tree. This will free up energy for the production of the fruit you actually want.
Sometimes, you will get a rootstock that just overpowers the graft. I have a clementine tree that is like this. For years, only the aggressive rootstock has thrived at the expense of the tree. Even though I aggressively cut back the rootstock sprouts, it continues to suck the life out of the graft. I'm now taking it out after 5 years in the ground and will find another, more suitable replacement.
Do some reading on rootstocks that are geared towards your local climate and soils - that will go a long way to you having healthy, productive trees.
John Elliott wrote:Can these shoots be used as new rootstocks? Can one divide them from the main trunk and grow them to say 1/2" in diameter and then graft them with a desired apple?
Yes - they can. A friend and I air-rooted some of the aggressive citrus tree stalk (see my above post) by bending down some of the more pliable shoots and tacking them down against the soil with landscape staples, then covering the parts laying against the soil with compost and mulch. If I remember correctly - it took about 2 months for roots to form from a leaf union and then the new plant could be clipped from the mother plant and repotted. My friend Ruby, a hardcore plantswoman, then took these new rootstocks and bud grafted varieties onto them. This was about 3 years ago - I need to check on the progress.
With some rootstocks (and some graft stock) you need to be cognizant of patents. You cannot (legally) reproduce patented rootstock or graft patented graft stock on other plants (otherwise I'd be spreading apriums far and wide because they are DELISH and grow well in the desert!)
There are tons of videos online showing how to air root plants and how to bud-graft. Check solutions for your part of the country because they will vary. For instance - October is the best time to do this in low desert in AZ.
I would create separate rootstocks by air-rooting (or other method) as opposed to keeping the various rootstock suckers on the tree. I think that would still overwhelm the graft stock in short order.
john hubbard wrote:I need to get rid of these sprouts by clipping or twisting but I should wait until the beginning of summer as opposed to doing it tomorrow?
My summer pruning advice may not be appropriate for your situation, maybe an expert will stop by
Also, it's usually recommended to summer prune in late summer once the tree has stopped growing strongly.
From what I understand, as you're entering winter, the tree will not be using any energy till spring so there's no rush to prune.
Most people try to prune at the end of winter so the tree breaks dormancy as soon as possible after pruning.
Generally, the less time the tree spends with open wounds, the better.
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