Blow or grow?

The Royal British Legion have decided to launch this year's poppy appeal by printing out John McCrae's famous poem "In Flanders Fields" in poppies at various sites around the country.  Except that they have chosen to use the version which starts "In Flanders fields the poppies blow....".  I was always taught that it should be "In Flanders fields the poppies grow...."  and indeed we have the poem written out by the man himself which quite clearly uses the word "grow".  So where did "blow" come from?  There are various theories but, given that the poet himself wrote it as "grow" surely that should be the definitive version?  Further, I think it gives the poem a nice symmetry - first line "In Flanders fields the poppies grow..." and the final line "though poppies grow in Flanders fields".