Mine is in a South facing garden. Full sun all day and the heat here does not kill it. You can prune it in winter or spring after the threat of frost is gone.

I winter sowed mine last year and planted it in the south facing garden. It is well drained also. I used top soil from my veggie garden which is really rich and sandy to a point. It grew to 2 feet. This year is already promising to hit its 3 foot mark.

The first time I grew a butterfly bush I planted it in a West garden. It died. I had two bushes last year and the one I put in the west garden died too. That garden got morning shade and noon on sun. Try a South location for it. I think that has made the difference for mine.

So maybe some evening shade?

Nah. Mine gets at least a full 8 hours of hot, beating sun. The only shade it would get is early morning. That garden has topsoil from my veggie garden and I watered it deep once a week.

Maybe that was the problem, not watering enough.

Could be.

Well, I'll try again and see if I can't get it to last more than two years.