I always start with a quick detailer spray 1st to see if you can get it off with that.

 

I've been telling people for decades, "never park under any tree," period. It's not so much about acorns. It's about bird droppings, sap, dew, leaves/needles, and the worst... if it rains, you get all the tree's dirt and oil on your paint.

 

Yes, it's about all of those things....but it's also sometimes about some badly-needed shade, particularly when the trees aren't dropping anything harmful.

 

One of the worst things is that artillery fungus (black spores). It's amazing how many people do not know what it is (I didn't until I looked it up last year), and think I'll just clay my car whenever. This stuff is amazingly ok to get off within a few days with a microfiber and water, but if left for a month, clay doesn't want to remove it...nasty. I've heard if it gets on your house, power washing cannot get it off of siding...

 

You don't need shade. Cars have UV protective glass, UV protective paint. if you keep them clean and protected, get the windows tinted for extra heat rejection they can sit out in the sun no problem.