Grassroots marketing efforts work for lawncare services, too.
But Robert's question is a good one.
Your efforts are probably going to be different depending upon whether you are interested in residential services, or maintenance and care of commercial properties.
An ad in the yellow pages can be costly, but it might deliver a nice return on your investment if people find you through it.
Were you counting the creation of a logo, business motto, van or truck decorations, letterhead, business cards, etc., in your marketing efforts?
Membership costs in a local "main street association" or chamber of commerce, and the time attending meetings of those organizations to network?
Word of mouth is a nice way to get business, and can be relatively inexpensive.
This link from the Small business Administration covers the basics of a marketing plan. If you go through and write up some answers to the questions they pose there, I think that you'll come up with some good ideas on how to market your business, even on a shoestring budget.
Since your objective is to target on finite number of accounts, you probably don't need to broadcast your business to the world. I suspect that if you could find a way to get in front of some prospective customers, you might be able to find some clients quickly.
If you put together some decent business cards and brochures, you might want to start out with joining a local commerce group, and attend some of their gatherings where you can talk to owners of businesses in a comfortable setting.