Do I have to scrub when cleaning vinyl siding? Can I just spray it on with a pump bottle and hose it off with a garden hose after it soaks a little?

In order to get a uniform and thoroughly clean surface, it is recommended to apply some light agitation when cleaning siding with Simple Green. A large soft bristle brush, something like a car wash brush, will give a much better finish than simply spraying on and rinsing. Spraying on with a pump sprayer and simply rinsing with a garden hose could also result in drip marks and streaks after the surface dries.

Yeah if you're siding isn't too bad a shape. Not too much mildew spots. You may have to scrub the bad ones that don't come out. Or use a little bit of bleach in your water.