I don't know why they disappeared, they thrived for several years. I don't remember when they were no longer growing, it might have been the dreadfully hard winter we had in 2010/11 when we had 7 weeks straight constantly below freezing, down to at least -17C with maximum temperature one day being -7C! That's not normal for here, some winters we only get about 4 frosts to -5C or a little lower.
