Well, it's a corollary, although not necessarily an obvious one, that long
summer days (of, say 16 sunlit hours) must exist only in places with short
winter days (8 sunlit hours) . Many lilacs are native to Eastern Europe -
places like Yugoslavia, Romania, Hungary. The latitude there is between 45
and 55. This is the same latitude as the northern tier of states in the US,
all along the Canadian border.
"Vox Humana" wrote in message
. ..

"paghat" wrote in message
news
In article , "Boots"
wrote:



#2 reason for never blooming is their narrow environmental requirements
aren't met. They need very warm summers with lots & lots of sunlight,
then
a good solid wintry winter for dormancy; they like rather northerly
climates with summer sun still shining at nine at night, followed short
winter days, like in central Europe or the Pacific Northwest.

I don't understand why short winter days would make any difference since
lilacs are deciduous.