I'm trying to write a sales letter to send to a large number of prospective clients, almost all residential, middle and upper-middle class accounts. I'm familiar outside of my landscaping to these people.
How long of a 'letter' do you want to do? If you have the time to make a newsletter-type piece with educational content, this can help to establish your stature as an 'expert' and make these people more inclined to call you. Possibly a mix of educational and marketing articles will work for you. Good Luck and let us see the result.
if you're gonna include some educational content try to tie it to something that always comes up in a customer to landscaper or neighbor to neighbor converstaion this year in our area you may consider doing some research on the abundance of spiders on properties..earlier this summer maybe something on all the rain (or lack of rain this fall)