In lawn care, the most profitable new customer is the one next door to an existing one. Marketing should reflect that.
Time the sign-up window
Most homeowners decide on a season plan in the first warm weeks of spring. Start advertising before that window opens, and stop sign-up ads once routes are full.
Build density on purpose
Target neighborhoods where you already have routes. An offer like "first mow free when you join your street's route" is honest, specific and good for margin.
Upsell in the fall
Aeration and overseeding are natural add-ons for existing customers. Promote them to your list before advertising them to new audiences.
Measure by route
Look at sign-ups by neighborhood, not just in total. A campaign that adds twenty customers scattered across the county may be worth less than one that adds ten on three streets.
See lawn care example ads and the free service-area planner.