I read this poem a long time ago, when you first posted it, and it always seemed to me to be something of an oddity, since it is so far outside the Harry-Ron-Hermione mainstream of the seven books.
I went back to The Goblet of Fire to refresh my memory about Frank Bryce. He was born in about 1918, so he would have been 21 at the outbreak of WWII. Bert was probably a couple of years younger, if Frank could push him in the wheelbarrow when they were children, probably in the late 1920’s. Is the streamlined silver arrow a brand of motorcar?
The Goblet of Fire tells us that Frank was wounded in the war; your poem implies that Bert was wounded, or worse, killed in the war, because Frank is now alone.
I pondered the line ”Earth means life and death.” I guess that it means life because Frank is a gardener, and grows plants in the earth, but it also means death because Bert was buried in the earth. So Frank is comparing his happy youth to the cataclysm of the war and its aftermath, long years of being crippled and alone. When he uses the old wheelbarrow, it reminds him of the brother and the happiness that he lost.
As is typical for your poetry, you write very compactly, and you package a lot of information into a short space, choosing the one word that precisely conveys what you mean, without talking all around the subject. For example, “I pushed, Bert perched…” I often spend long minutes searching for just the word I need, writing lists of almost-synonyms that encircle my desired meaning but never quite hit the target, finally giving up the task until the next day, when the sought-after word suddenly pops into my head. But it is worth it, in the long run, to get that one perfect word.
Sometimes I wonder if we writers will ever run out of things to say about the Potterverse, but it seems unlikely, since there are so many tiny characters, events, objects, all ripe for expansion into a story or poem. Like this one. Thank you for writing.