Mix cheap white vinegar 3 to 1 with warm water. 3 parts vinegar. Spray on with garden sprayer, wait 5 minutes then high pressure wash. Keep your nozzle 6 inches or less from surface, your siding will look like new.
"Be nice, until its time to not be nice" (Patrick Swayze...Roadhouse)
clorox and water...best siding cleaner ever. One part bleach to 5 parts water. Gets rid of everything. I had white siding on my last house that started turning green in the one shaded area. Sprayed the clorox on with a pump sprayer and hosed off. Clean as a whistle.
<span style="color: yellow">Trying to understand women is like trying to smell the color nine. -Ferrell</span>