Question
Hi, my oak tree is dropping little pellets and when the land on my patio if it is raining they become soft and discolour the cement. Is this from the tree or something else. It happens mostly overnight.  If there is a heavy rain I get a lot of these droppings.
Any suggestions aas to what it might be.
Thanks

Answer
Sounds like immature acorns. Acorns are the fruit of the oak tree and take two years to mature. IF the weather conditions are not normal the acorn will abort early. Oaks contain a chemical (The tannic acid or tannin ) that will stain where they lay. These nuts are high in tannins. Think of acorns like red wine which is
also high in tannins and can leave dark stains on clothing or
carpeting.

When the tannins are spread over a porous surface, like concrete, the
result is a dark stain with a greenish or golden cast that looks like
someone threw a pot of tea on your driveway. That is what is happening when the acorns fall onto your driveway and then the rain washes over them.

There are a couple of remedies you might try.

One the safest is to use a product called CLR.

This mixed with a little warm water and brushed on the area should
remove some of the stain. It might require a couple applications, or
you could try it full strength.

As with anything you should test a small inconspicuous area of your
driveway first to make sure there is no adverse effect.

We feel the best way to remove the stain is to use Muriatic Acid.

Usually available at hardware, paint or masonry supply stores.

This is a product that is extremely corrosive and poisonous, care
should be taken when using Muriatic Acid. Wear vinyl gloves, eye
protection and old clothes and shoes.

Mix 1 part acid to 20 parts water. It is important to add the acid to
the water. You can gradually add acid to the mixture to strengthen it.

Apply the acid with a scrub brush. The solution should bubble when
applied to the concrete, if it?s mixed strong enough.

Let it set one to two minutes and then flush with plenty of water fromthe garden hose.

This should brighten up your driveway nicely.