In regards to marketing, I think the best thing you can do is flyers. Create a nice flyers (black and white photocopies work just fine) and start passing them out in neighborhoods where you are already mowing. Repeat this every 4 months. That's how we grew fast in the beginning.
I admire that you set high goals. But I really think they are a little unrealistic. I used to set goals like that for myself (to go from 55 to 200 in one year) and then I quickly found out there was no way for that to happen. Once I got even close to 80 or 90, I was so freakin' busy I couldn't see straight. You can't quadruple the amount of accounts you have, with no experience hiring and managing emplolyees, having accounts managers, handling butt-loads of accounting book work, etc. and expect to be able to handle all of it. You'll soon be so overwhelmed with it all that it starts to fall apart.
I can't tell you how many customers we've LOST over the years because we were growing so quickly that I couldn't keep a good handle on my business.
And here's another thing! More accounts doesn't usually equate to a whole lot more money for you. In fact, growing quickly like that will usually equate to you making LESS money, at least for the short-term (first few years). Trust me on that one. I've learned the hard way. The faster you grow, the more trucks you need, the more operating capital you need, the more your accounts receivables become a huge problem, the more equipment you need, a bigger shop, more insurance, everything just starts going crazy! And before you know it, you're making all this money, but it's going out the door faster than you can make it. Every time you turn around another insurance payment is due or the crew just broke another mower and you need to buy a new one or you need to buy another truck, or whatever. It's always something.
I'm just telling you from experience to pace yourself. Maybe set a goal for this year to reach 90 customers. And keep every single one of them (as long as they are not crazy) happy! Do that, and you'll just start growing off of just referrals. You won't even need to market anymore. If you can keep 90 customers totally happy and run that business efficiently, you'll probably find that you'll get a good 3-5 referrals a month from those 90 customers, without even asking. Then, it just grows from there.
But honestly, be scared of that much growth. I wasn't. I didn't listen when people told me that. And I've paid the price. Slower growth will make you more income (for you to keep, not your business) and will keep you a lot less stressed and a lot more happy.