I am a little confused by my Nepeta "Walkers Low"...I love this plant, I have seven of them in different gardens. Three of them are returning with gusto, four of them bearly show signs of life. Has anyone had trouble with this plant, it was on my list of steadfast garden warriors. Of those lagging behind, they are all in full sun, three are new as of last spring, one has been around for at least three years. Any ideas?