This is such great line. Why? Because it's the one place in the poem where you get to see the speaker and his father in the same place at the same time. Of course they're separated by a window, but still – there's a connection.
Bends low, comes up twenty years away (7)
It's amazing how just one image – his father bending over in a garden – can conjure up such an old, vivid memory.
To scatter the new potatoes that we picked, Loving their cool hardness in our hands. (13-14)
In a way, potato farming brought the family together. Here we see father and son working together to plant. So how do you think the father might feel to find out his son will be a writer?
By God, the old man could handle a spade. Just like his old man. (15-16)
You know what's interesting about these lines? They tell us that it's not farming per se that runs in the family, but spade-handling. So it's not the job that these men pass down – it's the skill.
My grandfather cut more turf in a day (17)
Here we see the speaker remember the skill of his grandfather, just as he remembered the skill of his father. The speaker seems very connected to his paternal roots. We wonder if they feel the same way about their descendants.
[…] the curt cuts of an edge Through living roots awaken in my head. (26-27)
The mere sound of a shovel going into the ground reminds the speaker where he comes from and who his family is. Now that's some good hearing.
But I've no spade to follow men like them. (28)
So why does our speaker become a writer instead of a farmer, really? Here he would lead us to believe it's because he can't handle a spade as well as his father and grandfather. But could there be some other reason?