It is not dirt — it is alive
If your Orlando home has green patches on the siding, black streaks on the roof, or a driveway that looks gray no matter how much it rains, you are not looking at dirt. You are looking at living organisms — algae, mold, and mildew — thriving in exactly the climate they love. The good news: it is normal in Florida, it is fixable, and it is preventable once you understand what is happening.
Why Florida grows it so well
Humidity. Orlando's air stays damp most of the year. Algae and mold need moisture to grow, and Florida serves it constantly.
Heat. Warmth speeds up growth. A shaded wall in July is an incubator.
Rain. Daily summer downpours keep surfaces wet and spread spores from surface to surface.
Shade. The north side of a house — which never gets direct sun in our hemisphere — stays damp longest and greens up first. Big oaks and dense landscaping create the same effect anywhere they shade a wall.
Food. Pollen, dust, and organic debris coat every exterior surface each spring, giving growth a free meal. Limestone filler in asphalt shingles is literally food for the algae that causes black roof streaks.
Know what you are looking at
Green algae. The most common — powdery green patches on siding, fences, and concrete, worst on shaded and north-facing areas. Ugly but the easiest to remove.
Black roof streaks. Those dark stripes running down shingle roofs are a specific algae that feeds on limestone in the shingles. Beyond ugly, it holds moisture against the roof and shortens shingle life. It needs a roof soft wash — never high pressure.
Mildew on siding. Grayish-black speckling, often near the ground, under eaves, or around damp corners. Common on stucco and vinyl in humid months.
Black mold patches. Darker, thicker growth in persistently damp spots — behind bushes, under decks, on shaded concrete. Needs killing at the root, not just surface blasting.
The health angle, honestly
Outdoor mold and mildew are not the same as indoor mold, and a green driveway is not a medical emergency. But heavy growth near doors, windows, and AC intakes can aggravate allergies and asthma, especially in kids and sensitive adults — every breeze carries spores inside. If someone in your home reacts to the outdoors every time they step out, the green film on the siding near the front door may be part of the story. One safety note: never dry-scrub or dry-brush moldy siding yourself. That launches a cloud of spores into the air you are standing in. Wet methods — like professional soft washing — keep spores out of the air.
The surface damage angle
Growth does not just sit on surfaces — it attacks them. Algae roots into porous stucco and concrete, holding moisture against the material around the clock. On roofs, the black-streak algae eats the limestone filler and its dark color absorbs extra heat, aging shingles faster. On wood fences and decks, constant dampness from growth accelerates rot. On pavers and concrete, it makes surfaces slick — a real slip hazard around pools. What starts as cosmetic becomes structural if ignored for years.
Why soft washing is the fix
Blasting algae off with high pressure removes what you can see and leaves the roots alive in the pores — so it grows back in months. Soft washing applies a cleaning solution that kills the organisms down to the root, then rinses gently. The surface stays clean for a year or more instead of a season. For siding, that means our house soft wash; for roofs, a dedicated roof soft wash; for concrete and patios and decks, a treatment wash that kills before it rinses.
Keeping it from coming back
You cannot change Florida's climate, but you can make your home less inviting. Trim trees and bushes back from the house so walls get sun and airflow. Keep gutters clean so water does not spill down siding. Fix drainage so water does not pool against the foundation or on flat concrete. Let sunlight in wherever you can — sun is the cheapest mold prevention there is. And keep the annual wash on the calendar: yearly treatment never lets growth get a deep foothold.
Tired of the green? Request a free quote from Orlando Pressure Washing Pros — we kill it at the root so it stays gone.
Frequently asked questions
What are the black streaks on my roof?
A blue-green algae that feeds on the limestone filler in asphalt shingles. It is extremely common in Florida's humidity. It holds moisture against the roof and shortens shingle life, so it is worth treating — with a low-pressure soft wash, never high pressure.
Is the green stuff on my siding dangerous?
For most people it is mainly ugly, but heavy growth near doors, windows, and AC intakes can aggravate allergies and asthma. And it damages surfaces over time by holding moisture against them. It is worth removing for comfort and for the health of your siding.
Why does it always come back on the north side first?
The north side never gets direct sun, so it stays damp the longest after rain and dew. Damp plus warm equals growth. Trimming back shade and improving airflow helps, but the north side will always need washing a little more often.
Can I just bleach it myself?
Household bleach can lighten surface growth, but applied wrong it damages plants, discolors siding, and does not reliably kill roots in porous surfaces. Professional soft-wash solutions are formulated, diluted, and rinsed properly — and the crew protects your landscaping. DIY bleach jobs are how flower beds die.
How long will it stay clean after a soft wash?
Typically a year or more for siding, because the treatment kills growth at the root. Shaded, damp areas may need attention sooner. Annual washing keeps growth from ever getting re-established.