When the spade sinks into gravelly ground: (4)
The sounds of the earth are so familiar to our speaker that they send him into a spiral of memories.
Till his straining rump among the flowerbeds (6)
What we can't help but notice is that the nature he describes is not wilderness. It's farms and gardens – places where man controls nature.
To scatter new potatoes that we picked,Loving their cool hardness in our hands. (13-14)
This passage shows both how close the family worked to the land, and how much they loved what it produced.