Have you ever considered offering a buy one get one free lawn care marketing concept?
Would something like this work?
Maybe it could be used as a referral where a current customer could offer a free lawn mowing to a neighbor for free as long as they were paying for their own lawn mowing.
Or maybe you could hand out flyers that said buy one get one free and have a free coupon for a neighbor lawn cut? This could promote someone to want to use your service and then bring their neighbor in as well. Maybe they would split the price between each other?