Book  (Oct 2001)  Page(s) 164.  Includes photo(s).

Book  (11 Oct 2000)  Page(s) 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...