Thread graft on crabapple - possible?

[TimIAm]

I've been waiting for a suitable bud to fill out the gap on this crabapple. It's only just started to throw out spring growth, so it fills out well on the left hand side, but nothing above branch number one on the right.

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The trunk is about an inch in diameter. I'm considering doing a thread graft (drilling through the trunk and threading the new growth through the hole) as there is a new bud (circled in the pic below) that is in a good place to approach the thread graft from the left hand side.

Does anyone have any suggestions either for or against this approach or advice on a better approach? My main concern is the chance of the graft healing properly. You can see where I've covered the original trunk chop and it's taken about 3 years to get close to healing over, but I think it will take at least another two. This tree doesn't seem to heal scars very quickly, but on the other side, the main attraction of a crabapple is when it's flowering, so it also hides it well.

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[treeman]

Thread graft is ok but ideally you need to grow a branch for it the year before. Even better let 2 or 3 grow long and you can do several at once.

[shibui]

Agree with Mike. There's a long way between a tiny bud and a shoot long enough to thread graft with. that it develops into vegetative shoot and not another short fruiting spur.
Nothing wrong with the plan - crabs graft quite easily and thread graft should be no problem - but you need to allow for the full time scale to bring it to fruition.
Another option you could try while waiting for that shoot to grow is to try cutting the bark above where you want the new branch. Auxins coming down from apical shoots tend to suppress new buds but if we cut through the bark and cambium to the wood that can temporarily restrict flow down the trunk and allow buds to grow. Not 100% effective and definitely relies on dormant buds being there under the bark but it can work in some cases and I have not seen or heard of negative effects even if no shoot emerges.

Surprised to hear you think crabs do not heal well. Crab apples heal relatively well but healing cuts relies on growth. Healing over cuts is limited when any species has restricted growth and speeds up when the tree is allowed to grow. Some more care, fertiliser and maybe some extra space for roots should allow more growth and faster healing. Sometimes apples start to concentrate on fruiting spurs and forget to put out vegetative growth shoots. maybe some high N fert might spur on some vegetative shoots?

[Sno]

Apples are very commonly ‘bud grafted ‘ . Plenty of videos on how to do it on YouTube .

[TimIAm]

Thanks all for the great advice.

Sno, I didn't consider bud grafting. I can see that working, so I'll do some reading and it may be the way I go.

Neil, I can see what you are saying about being a long way to go. My thinking was to not wait until I had something too big = bigger hole to drill through. I have also had some battles with getting good branch structure down low as branches get brittle very quickly. Sometimes I have had to wait to see what branching I have available before wiring which has sometimes lead to a snapped branch.

I didn't want to make a generalisation about all crabs, but this tree does have quite a few scars. I just wanted to check to get some advice in case this wasn't the best approach. There is a decent sized wire scar near the top that isn't healing well. It may also be in my quest to refine branching last year that I slowed down growth / healing through repeated cut backs. (on the plus side, I'm very happy with the branching down low).

Just started applying spring ferts. This year I will be letting it grow out more but would love to see that gap filled in. I'm also thinking that I need to regularly rotate it during early spring next year in order to get more balanced flowering over the entire tree. I kinda had it facing the sun on one side and you can see the majority of early spring growth has been on one side.