According to The Oregonian, it might be a good idea to just let your annuals go at the end of the season.
There is a chance that annuals will come back the following spring if the winter is mild. So, instead of deadheading and removing summer’s plants, leave flowers alone when summer ends. Seeds from flowers and plants can be spread by birds and the wind.
From The Oregonian:
“Good seed setters include sweet peas, sunflowers, calendula, borage, nasturtiums and annual delphiniums. Common garden and Flanders poppies, clarkia, alyssum and even petunias will come back year after year, depending on winter’s severity.”
Via: The Oregonian > Let sunflowers, sweet peas and other annuals go to seed: Gardening basics
