 I will tell you that mine has been in my yard in excess of 20 years, and some years it dies to the ground and then regrows back up again. Other years, it doesn't do that, so I don't know what it is. To be frank with you, mine, I would say, is probably a borderline six and seven. In cooler climates, it may be severely pruned back to the ground and will usually regrow and usually produce almost seven to eight feet of new growth each year.