Concrete in the Lowcountry rarely just gets dirty, it grows something. Our humidity keeps slabs damp, and any surface that stays damp and shaded will green over with algae, the slick film that shows up first along driveway edges and on the north side of a house. Around Bluffton, homes under mature canopy see it fastest: driveways and walkways near Old Town Bluffton and the shaded lots around Belfair Towne Village often show growth well before a sunnier slab a mile away.
Tree cover adds a second layer. Live oaks release tannins that leach into porous concrete and leave brown staining behind, and those same oaks drop leaf litter that traps moisture wherever it settles. Spring pollen then cakes onto everything and feeds the organic growth already established.
Salt matters here too, though differently than it does on glass. Salt-laden air keeps surfaces from drying out fully, and on paver driveways it works down into the sand joints, where the persistent dampness encourages weeds and moss between the stones rather than staining across the top. Older concrete is more vulnerable throughout, because a weathered slab is more porous and holds both moisture and staining far more readily than a freshly sealed surface.
