Clematis which flower both on old ripened wood and, again later in the season, on new growth. Group 2 does not require major pruning but dead and weak stems should be taken out. Pruning to control overgrowth should be done immediately AFTER the first flowering period ends.
[From Clematis For Everyone
, p. 9:] Some of the varieties that belong to this group are: 'Nelly Moser'
, 'The President'
, 'Vyvyan Pennell'
, and 'Marie Boisselot'
[Ibid, p. 11:]... very early flowering cultivars of the early large-flowered section such as 'Edith' or 'Dawn' should be planted where they will receive some direct sunlight... [if not they are] susceptible to the unwanted greening of flowers [see also FAQ: Why is the flower green?]... and are not recommended for a north-facing positon...