I have 2 long established clematis in my garden, 20 years or more, one is a Montana and the other I don't know the name. This one didn't show any growth about six or seven years back but it recovered fully the following year. I thought it was perhaps that I had washed the patio next to it with a mix containing Sodium Hypochlorite, but it has been fine since. This year however neither of them has flowered, no buds or leaves. Could it have been the exceptionally cold winter? The pampas grass in the garden has also failed but after cutting it down to the ground new shoots appeared quickly. Any ideas?