Why have poppies become the flower of Veterans, Remembrance and Memorial Day?

 An enduring tradition began in WWI, after John McCrae composed the following classic work ...

In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.

We are the Dead. Short days ago,
We lived, felt dawn, saw sunset glow,
Loved and were loved, and now we lie
In Flanders fields.

Take up our quarrel with the foe
To you from failing hands we throw
The torch; be yours to hold it high.
If ye break faith with us who die
We shall not sleep, though poppies grow
In Flanders fields.

To this day, McCrae's "In Flanders Fields" remains one of the most memorable war poems ever written.  It a lasting legacy of the terrible battle in the Ypres salient of France that occurred in the spring of 1915.  The story behind its drafting  is sobering.  As a surgeon holding the rank of Major attached to the 1st Field Artillery Brigade, McCrae spent seventeen terrible days treating injured men -- Canadians, British, Indians, French and Germans ---  in a long trial of bloodshed, screams, horror and brutal suffering.   

One death in particular touched him.  A young friend and former classroom student, Lieutenant Alexis Helmer of Ottawa, was killed by a shellburst on 2 May 1915.  Lieutenant Helmer was buried in a small cemetery outside McCrae's dressing station, and McCrae had performed the funeral ceremony in the absence of a chaplain.

The following day, sitting on the back of an ambulance beside the Canal de l'Yser,  McCrae vented his deep anguish by penning a poem.  From where he perched, McCrae could view wild poppies that sprang up from ditches in that part of Europe.  He spent twenty minutes of precious rest time scribbling fifteen lines of verse in a field notebook.

Those words came close to never being seen publicly.  Dissatisfied with his composition, McCrae tossed the work away.  It was actually a fellow officer who came across the discarded piece and, moved by what he read, forwarded it on to  newspapers in England.  Rejected by one publisher,  "In Flanders Field" eventually ran in London's "Punch  Magazine" on 8 December 1915.  It gained wide recognition from there, and by 1918, McCrae's poem was known throughout the allied world.

In America, a woman by the name of Moina Michael drafted her own poetic words in fitting follow-up ...

We cherish too, the Poppy red 
That grows on fields where valor led, 
It seems to signal to the skies 
That blood of heroes never dies

Moina Michael fashioned the custom of wearing a red poppy in memory of war's sacrifices, and established it as a symbol of keeping faith.  A French women, Madam Guerin, learned of this practice while visiting the United States, and took the symbolism further and abroad. Upon her return to Europe, Guerin began creating hand-made poppies that were sold to raise money for benefit of orphaned children and destitute women in war-torn France.  The tradition spread to Canada, the United States and Australia.  It has endured until today and has become closely associated with days of ceremonial recognition and observance that honor fighting forces in these countries.