WIBU not to attend this follow-up of my grandmother's funeral?

[Venusfire]

My grandmother passed away a couple of days ago In a way, it came as a relief - despite obviously being very sad - as she was old and her mind had been ravaged by dementia.
Her funeral is in a couple of weeks' time, mid week. It goes without saying that I shall take the day off work and attend. It's a 3 hour journey each way, which is absolutely fine.
My mother (her daughter) would like us to get together again on the weekend after to plant a tree in her memory - at her allotment, not randomly!
I think that's a beautiful thing to do, but my eldest child moves out of home permanently on the Monday morning. I'd like to spend time with her, to help her pack and get ready, and also prepare her bedroom for her younger sister who is moving in there.
The rest of my family are a 15 - 20 minute drive away from the place. But I'll have the 3 hour journey each way again.
WIBU not to attend the tree planting? I feel heartless but would rather prioritise my own kids.
Thanks for reading.

Why not suggest a different date to your mum and ask for it to be a week later? Or is there her wedding anniversary or birthday coming up that you could suggest?

My dB lives 3 hours away. He comes to very important unmissable family occasions like funerals but he would not come back the following week for a tree planting. He has family commitments, work, inlaw support etc. We all understand that. Just factually explain to your mom that it's not possible and leave it at that. Could you join in remotely for a short while?

YANBU

Yanbu. It’s very reasonable to not attend for that ceremony. My sister never attended our grandmothers funeral for reasons about her childrens needs. And that was fine and it was her actual funeral. Just let your mum know you’ll be thinking of her.

YANBU
In my family we would discuss dates for such events and agree on one that was OK for everyone. Or accept that not everyone can be there.

Are they going to keep the allotment? Because otherwise the next allotment keeper could just decide they don't want the tree.

My mother was very much of the opinion that ‘life is for the living’ so I would prioritise my child and myself over the tree planting but stop and raise a glass at the time it was going ahead.
Sorry for your loss.

You’re not unreasonable at all. If you want to be involved at all could a family member have you on Zoom/Teams as the tree is planted so you can see with no travel?

Thanks everyone. I'm glad I'm not being uncaring. I loved her very much and she was hugely inspirational to me.
But, she's gone.
I've asked mum if we could possibly do it another time, or not to feel bad at all if they go ahead without me.

My daughter moves out for university in a couple of weeks time. I am.not doing anything that weekend but spend it with her. I wouldn't be spending 6 hours of it sitting in a car for anyone but her. So I don't think you are BU at all.

Planting a tree is a lovely idea but it's not essential. What would your grandmother want you to do? In your shoes, I'd have a chat with my grandma on the morning of the day. Tell her how important she was, explain why I wouldn't be there and tell her about your daughter and this exciting new chapter in her life. I talked to my grandma quite a bit after she died!

Will the tree be in a place you can visit after it's planted? I hope so. Then you can go in a few weeks when you have more time @Venusfire and see how the tree is doing, encourage it along, and spend some time talking to or thinking about your grandmother and the tree will become one of the places you remember her.
Planting it is only the beginning of your family's relationship with the tree, surely?
I'm so sorry for your loss.

I hope your mum agrees to a different date. If it is a few weeks later it might be more of a celebration of her life in a way, given the time gap from the funeral.