giant Asters

These giant Asters we once grew in our garden in Oakland. I was given them by a gardening friend who knew nothing about them (even that they were Asters!). They grew easily for us - in fact they continued to grow all year long, getting higher and higher, much higher than they did for my friend. Finally, they burst into hundreds (thousands?) of flowers all over their top half.
These flowers stopped traffic - literally. We then lived next to an traffic intersection. The huge mass of these lavender flowers caused people to slow down and even come to a full stop while driving by. This was especially true at dusk, when the bluishness of the flowers would start to glow with the half-light of the evening.
After about a month of this, the flowers were all gone, the tall, stiff stems had to be cut down and tiny little basal shoots would start the whole annual cycle all over again. Eventually, it was all too much to deal with and to devote such a large area of the garden to (these Asters spread at their roots significantly each year!). They had to go, but I still miss them.