It sounds like an "as needed" basis for some things, if you're treating a disease or pest. And it sounds like a monthly drench with some and a weekly foliar feeding with others of these products isn't too often.
Have you visited the Garden Maintenance Calendars they have here at the site? This is a link: http://www.dirtdoctor.com/organic/garden/view_question/id/2922/
I know I've heard Howard talk about how frequently he uses Thrive and Plant Wash, but couldn't quote him. To find it simply call around to your area use the Organic Businesses page http://www.dirtdoctor.com/organic/garden/advance_business_listings/
. I need to start using a couple of these, and plan to read the instructions on the package closely and go from there.