I have typically sent out renewals in Feb/early March. I guess, I enjoy the initial time off when I finish up a season as well as I figure my customers get a break from their lawn expense too! Not saying that my way is right though. Seems I see competition sending out their info sooner very year. Of course I don't worry much about competition at least concerning existing customers.
I typically do price increases just like you. Very rarely on a new customer for the same reason. Same as increases to the older ones that have fallen behind concerning costs.
How do you do renewals? I send out letters to every customer, but it states that renewal is automatic unless I am contacted and told otherwise. One thing that I have never done but I see some bigger companies do is push to upsell services right from spring as a total package. For example aeration. I have always offered that when the time comes in the year. I am thinking about somehow adding that in with a discount if the customer commits in the spring.
Or another idea, that I suspect others do is, renew the entire service the same as last year. For example, if last years service was 5 or 6 apps, grub control and aeration, that whole program is automatically renewed as performed the prior year. Less nagging the customer and automatic service to them and business for the company.