One way you can get a general feel for whether customers in your area are searching for your services at a particular time, is to use Google Trends.
For example, I have input the following criteria:
- keyword is "lawn care" (you need to enter whatever the best search terms are for your area)
- location - U.S. > Michigan (filter down to state level using the map at the bottom)
- showing last 12 months
You can see from the graph, week by week, when people are searching online.
You will notice that the current week (10-16 March 2013) is showing a steep upwards trend, which indicates people are starting to think more seriously about it.
Of course, this is showing data for the whole state of Michigan, and I'm sure there will be variations between different climatic areas in the state.
Anyway, just thought this could be another tool to help you keep an eye on customer search behaviour, so you can optimise when you send out any marketing material which is dependent on getting the timing right.