We usually pass out fliers every month during the growing season. We hit the same neighborhoods at 3 times, yes the same 1, and yes 3 months in a row.
Suggestion: Get a website and get it SEO(optimized)
I haven't been in the phonebook for over 2 years and we continuously grow every year ever since. All of our clients have been either word of mouth or articles I've written or our website.
Back to your question: March is a great time to start, find the neighborhoods you want to pick up accounts and re-visit them every month