Fond Memories is not Viticella Group, it is Late Large Flowered Group. If you have planted your Group 3 clematis with the crowns 4 to 5 inches below ground, then you can chop the old stems back to ground level, they will shoot new stems, more flowering stems every year, from below ground.
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.