Here is an idea to help raise awareness of your lawn care business and clean up a local park at the same time.
What if you put together am "It's my park day." You could hand out flyers in your area and look to get some local volunteers to come and help you clean up a local park or a local township eyesore. You could probably promote this for free in the local paper and then later, show off before and after pictures of what you did by sending pics to the local paper. You could also include these on your site.
As you build up a list of volunteers, you could have them put up lawn signs as the event got closer to promote the project and have your business number or website be the place to get more information.
Here are some picture examples of a flyer and a key chain. You could do this almost any season of the year!