Is there an easy way to clean acorn stains off of concrete?

Try using a pressure washer.

wet and forget

Power washer and a little driveway cleaner sold in home stores will do the trick. I suggest wetting first put on cleaner and wait few minutes then use a stiff brush and power wash. It should come out good as new. Take it a step further and trim branches that hang over concrete if possible

The cheapest and easiest thing we've found for concrete and vinyl siding is bleach with a little dish detergent. We use the 5 gal bug sprayer. Put roughly 3" high of bleach, then fill with water, then add about a tablespoon of dish detergent. VERY IMPORTANT add dish detergent last. Then just spray the affected area, let it sit maybe 15 min. and then just rinse off with your hose. It removed stubborn rust stains off of vinyl for us, so should work like a charm on the nut stains.

Try some of these techniques.

WD-40. Did a leaky oil pan leave a big ugly spot in the middle of your concrete driveway? To get rid of an unsightly oil spot, just spray it with a generous amount of WD-40 and then hose it down with water.

Soda (Coca Cola). Here’s how to remove oil stains from concrete drive-ways and garage floors: Gather up a small bag of cat litter, a few cans of cola, a stiff bristle broom, bucket, laundry detergent, bleach, eye protection, and rubber gloves. Cover the stain with a thin layer of cat litter and brush it in. Sweep up the litter and pour cola to cover the area. Work the cola in with a bristle broom, and leave the cola for about twenty minutes. Mix 1/4 cup laundry detergent with 1/4 cup bleach in 1 gallon (3.7 liters) warm water and use it to mop up the mess.

Oven Cleaner. Get those unsightly grease, oil, and transmission fluid stains off your concrete driveway or garage floor. Spray them with Easy Off No Fume Oven Cleaner in the BLUE can. Let it settle for 5-10 minutes, then scrub with a stiff brush and rinse it off with your garden hose at its highest pressure. Severe stains may require a second application.

Kool-Aid. Nasty rust stains on your concrete? Mix unsweetened lemonade Kool-Aid with hot water. Scrub and the rust stain should come right out.

Baking Soda. Salt and commercial ice-melt formulations can stain — or actually eat away — the concrete around your house. For an effective, but completely innocuous, way to melt the ice on your steps and walkways during those cold winter months, try sprinkling them with generous amounts of baking soda. Add some sand for improved traction.

Ammonia. Tired of those annoying discolorations on your concrete work? To get rid of them, scrub with 1 cup ammonia diluted in 1 gallon (3.7 liters) water. Hose it down well when you’re done.