Fall comes every year and every year the fallen leaves leave shadows on the sidewalks, parking lots and driveways. After a few years, one might begin to wonder why.
Although there are quite a few theories, the most commonly accepted is that of tannic acid. Tannins have been used to make ink, to tan leather and even are responsible for the color in tea. They are also soluble in water, which, in our rainy Vancouver climate, makes a good deal of sense. Although this answer is not definite, it is certainly plausible and might make an interesting Thanksgiving conversation.
The ghost like stains left on our sidewalks may be beautiful but they are not always welcome. The stains can be hard to remove but a good detergent, preferably with a bleaching agent, and a good, solid scrub should do the job. Remember to wear old clothes that can be ruined by the bleach. First, clear away all the dead leaves with a power washer (for tips on using these, see Decks & Patios) and apply the detergent. Let it sit for a few minutes or follow the instructions on the label. Scrub vigorously with a non-metal brush and rinse.
If the stain is still there, repeat. To avoid blotchiness on account of the bleach, try cleaning a larger area. Please use bleach sparingly to minimize damage to the environment and remember that power washers are powerful machinery.
Have a wonderful Thanksgiving from the team!