How many clematis to buy This question was asked by – WENDY I have had an ugly Leylandii hedge cut down to waist height and want to plant clematis to cover the remains. I wonder if you could suggest how many plants to cover about 35 feet in length, please? hi wendy the average spread of the average clematis is about 1 metre so that would mean about 10 plants however you could cover it all with just 2 of the Montana types but they only flower in may where as the others tend to flower for about 3-4 months (so horses for courses) hope this helps Clematis – Montana Chris and Suzy