Depends on who you're gearing yourself towards. If its Commercial Property Managements it really varies. Some sign all inclusive contracts some sign seasonal contracts. I have just been awarded a few landscaping contracts and we're about to go into winter. So it really depends, It never hurts to ask though.
But its definitely something that you can work on year round. I do sales and during the summer is the hardest time to talk about snow to some people. I get the line "Its 90* and sunny outside... No ones thinking about snow" a lot! But it really just depends....