To ask stranger if I can dig up their tree in the garden?

I wouldn’t, for the simple reason that as a pp said it can be difficult to transplant mature trees and if you moved it and it dies I think you would feel really awful. Can you not reframe it in your mind as growing happily in the place where your mum put it?

Would you consider buying the same one in honour of your parents and planting it in your garden?I think this has a better chance of survival. Plus how gutted will yoh be if you move it and it dies, which it has a very high chance of.

Taking a cutting from it would likely ensure the survival of the old tree and a knew tree would flourish. I don’t think it’s odd to ask though. If you want to take the whole thing, do ask a tree surgeon.

I would ask them for a cutting from the tree if that's possible. Cherry trees are prolific and spread like crazy. I'm sure you could grow a baby from the original tree.

Our cherry trees haven't been the same since we paved our front drive. They are still in the same spot with the same roots.

I would not risk transplanting it personally. Plant a tree in your garden in memory. Do it with your kids. Make a new memory.

The issue would be whether it would transplant well or not. I say this because I dug up a well established small cherry tree and moved it elsewhere in my garden. Sadly it didn't survive. Transplant plant shock is a thing. I recommend purchasing a similar tree from a nursery and planting that in your garden and getting the kids to nurture it. My feeling is that even if you got permission to dig it up fine the original garden and then it didn't survive this might be even sadder for you.

Certainly worth asking. I would worry it will be difficult to take up and re-establish elsewhere if it’s a mature tree, though — would it upset you more if you transplanted it and it died?

Or you could ask to take a few cuttings, and hopefully one of those would establish.

You can ask but don't be surprised at all if they say no. If it's that well established it would be a major undertaking to dig it up and move it safely (think jcb, crane, flatbed hgv), and there's no guarantee it will thrive in it's new location.

Why not try and reframe your thoughts, and smile when you see it, imaging new families and generations enjoying it as your dad did.

Maybe knock and ask for a cutting to pot and grow your own offshoot tree?

Ask. If they say no because they love the tree then you may have some peace knowing that it’s still being treasured.

I'd assume the cherry is very well established after 12 years and it would cause considerable damage to remove it (potentially to the tree as well as the garden). It would be worse to take it and the tree die than it flourish and grow in a garden your parents loved.
I do feel for you. Can you buy the same breed of cherry and plant it as a tribute to your parents?

I think you wouldn’t be u to send them a very polite letter and ask, but it’s worth thinking through all the associated costs and risks, and definitely don’t doorstep them about it.

Before you write that I think you should - if you haven’t already - do some careful research into what’s involved in digging up a 12 year old tree and how it may not survive transplantation. You’d also need to pay to make good the new occupants’ garden because the roots will be very extensive.

I would ask. All the can say is no. Could you maybe offer to replace it with something of their choice?

Sorry for your loss. A mature tree would be very difficult to transplant and not guaranteed to survive the move, even if they did agree (which I also think is unlikely).
I would try and move on from the original tree and plant another lovely tree (or trees) in your parents memory.

You can certainly ask.