It's hard for me to make a suggestion since I don't know your market, or what you currently charge, or the quality of your work, or when you last raised prices, or what your market will bear.
If you haven't increased prices in a year or two, most of your existing customers will probably go along with the increase as long as you can justify the increase. Write a letter to all your clients which explains why you are forced to raise the cost of their service, when the increased rate will go into effect and how much the increase will be.
Explain that over the last 2 years (or whenever their last increase was) fuel prices for the mowers and for your vehicle have increased by x.x%, insurance costs has increased by x.x%, maintenance costs for the equipment has increased by x.x%, postage costs have increased by x.x%, increased time & costs associated with billing & check processing, etc. Explain that your company has absorbed these increases over the past 2 years but in order to provide them with the same quality of service you will be increasing the cost of their service by x.x%. This is also a great time to announce that you are now offering paperless billing and online bill payment "for their convenience".
Then give them their numbers:
Old rate from 2011 to 2013: $60
8.5% of $60: $5.10
New rate effective 1/1/14: $65.10 for paperless billing & online bill payment only
If you wish to receive a paper bill and require check processing, an additional charge of $6.25 will be applied to each invoice.
Make sure to thank them for their business.
A. W. Landscapers, Inc.
Hustler X-One 60"
Wright Stander RH 36"
eXmark 21" ECXKA21 Mower
Stihl FC110 Edger
Stihl FS90 Trimmer
Stihl FS55R Trimmer
Stihl HS56C Hedge Trimmer
RedMax EBZ7100 Blower
Husqvarna 440 18" Chainsaw
GMC Savana 2500
7' x 16' Enclosed V-Nose Trailer