If you are trying to weed out some customers to make room for more landscape project work why don't you just pick the ones you don't want and inform them that "due to a shift in our company focus we will not be providing lawncare services for your property next year. Loved doing business with you.. blah blah.....if you need help finding a suitable replacement blah blah....
This way you get rid of the ones you really don't want. The way you are describing sounds like you will lose some of your best accounts. Not a good idea.
Just a thought.