I feel like a memesheep geek.
We had a huge lilac bush (grove?) at the end of the house I grew up in, tough enough to climb on and swing on the limbs (for a small kid) and below it a shoulder of rock which was just the right size for a small kid to lay on. I'm very fond of lilacs. So it made me happy that Pratchett used it as the flower of rememberance (for those who died in an uprising) in "Night Watch." (Although, happy, but a little co-opted - now everyone will love lilacs and they won't be as special to me anymore.)
Friday I saw lilacs for the first time this spring, which always puts me in a good mood, and when I got home
Geraniums are the official flower for Memorial Day (coming up next weekend) and Memorial Day is the official beginning of summer in Maine. Lilacs mark the beginning of summer - maybe as a kid I was so fond of them because seeing them meant school would be out soon? But it also seems right that they be linked with rememberance fo the dead.