Sweet Autumn Clematis Pergola . I would like to be sure it can be controlled and not turn into an invasive vine. When the vine explodes into bloom in late summer and early. My Sweet Autumn Clematis...my husband had to build a special trellis from www.pinterest.com You also want to be aggressive when pruning (hard pruning). By next year i expect it will reach the pergola top. It can grow to 30 feet, though 15 feet is a more typical mature size.