The short answer
The green film on vinyl siding is usually algae and mildew growing on dirt and pollen where the wall stays damp and shaded. The safe fix is a low-pressure soft wash with a mild cleaner and a full rinse, not a high-pressure blast that pushes water behind the panels. Fall, before the first freeze, is a good time to do it.
If you searched for siding cleaning New York because one side of your house has turned green, you are looking at one of the most common outdoor problems in the area. Light vinyl shows it first: a green haze near the bottom and dark streaks under the gutters.
Most people know Green Choice for green rug and carpet cleaning in NYC. The same family-owned company, in business since 2005, also washes siding, decks, roofs and driveways. Here is what the green stuff is, what you can safely do yourself and when a soft wash makes sense.
Shade feeds it
Walls that stay damp the longest turn green first.
Low pressure wins
The cleaner does the work, not a hard stream of water.
Rinse matters
Cleaner left to dry on the wall leaves streaks and marks.
Fall timing
Wash before the first freeze, while growth is still fresh.
01. What the green film and black spots really are
The green haze on siding is usually a mix of algae and mildew living on a thin layer of dust, pollen and tree sap. Vinyl itself feeds nothing, but the grime on it does.
Black dots and gray patches are often mildew. Dark streaks under gutters and sills come from dirty water running down the same path every rain. Orange or rust-colored marks are a different problem: they often come from sprinkler water with iron in it or from metal fixtures, and they need a different cleaner.
02. Why one side of the house turns green first
The north wall, which gets the least sun, is usually the greenest. Other hot spots:
- Walls that stay wet for hours after rain or morning dew.
- Siding behind foundation shrubs, where air cannot move.
- The bottom row of panels, splashed by rain bouncing off soil and mulch.
- Houses near the water on the South Shore, the North Shore and the East End.
In Queens and the Bronx, the narrow side alley between two houses never sees the sun, and that strip turns green first.
03. Why high pressure is the wrong tool for vinyl
A rented machine looks like the quick fix, but a hard stream aimed upward can drive water behind the overlapping panels and around window frames, chip trim paint and leave stripes on older siding.
In its cleaning tips, the Vinyl Siding Institute recommends a hose, mild soap and a long-handled soft-bristle brush. It says that if you do use a pressure washer, the stream should stay at eye level and point straight at the siding, not at an angle, so water is not driven in behind it. It also notes that some manufacturers do not want pressure washers used on their products at all.
Don’t spray upward
Water aimed up under the panel laps ends up behind the siding, where it cannot dry.
Don’t use undiluted bleach
The Vinyl Siding Institute warns against it. It also harms plants.
Don’t reach for solvents
Organic solvents, liquid grease removers, nail polish remover and furniture polish are on the list to avoid.
Don’t let soap dry
Soapy water that dries on the wall leaves marks.
04. What you can safely do yourself
For a small patch you can reach from the ground, wet the wall, scrub a small section with a soft brush and water with a little dish soap, and rinse from the top down before it dries.
The same Vinyl Siding Institute tips say that small spots of mold and mildew can be cleaned with common all-purpose household cleaners, and suggest a mix of 30 percent vinegar and 70 percent water for stains.
It stops making sense on second-story walls, gable peaks or a whole side of the house. Ladders and wet siding are a bad mix, and a half-cleaned wall looks worse than an evenly dirty one.
Tip: test before you wash the whole wall
Try any cleaner on a small spot low on the wall, behind a shrub, and let it dry. If the color or shine changes, stop.
05. Soft washing vs. power washing compared
People use both words for the same job, but they are different methods, and vinyl siding needs the gentle one.
| Method | How it works | Best for | Risk on vinyl |
|---|---|---|---|
| Hose and soft brush | Mild soap and hand scrubbing | Small first-floor patches | Low, but slow, and high areas are hard to reach |
| Soft washing | Low-pressure spray of a cleaner that loosens growth, then a gentle rinse | Whole houses, two-story walls, green and black growth | Low when products are mixed and rinsed correctly |
| High-pressure washing | Narrow, powerful stream that knocks dirt off | Concrete, pavers and some masonry | High: water behind panels, damaged trim, stripes |
06. How a professional siding wash works
Our power washing service treats siding as a soft wash: low pressure, the right cleaner and plenty of rinse water.
- Walk the house. We check for loose panels, open vents, outlets and plants close to the wall, and point out marks like rust that need another treatment.
- Protect the area. Windows are closed, fixtures covered and shrubs wet down before and after.
- Apply the cleaner at low pressure. An eco-safe cleaner goes on from the bottom up and sits long enough to loosen the growth.
- Brush the heavy spots. Thick growth gets a soft brush, not more pressure.
- Rinse from the top down. Every section, frame and sill is rinsed so nothing dries on the wall.
- Final walk-around. Each side is checked and spot-treated if needed.
Honest expectations
Green algae and fresh mildew usually rinse away completely. Old black spots in textured corners, rust from sprinkler water and fading on very old, chalky siding may only lighten. We tell you which is which before any work begins, and the price is confirmed with you before we start.
Is one side of your house turning green?
Get a free quote for a gentle soft wash. Same-day or next-day in most areas, and 10% off your first cleaning.
Get a free quote → Call 1-800-589-436407. Why fall is a good time to wash siding
Fall is a smart time to wash. The summer’s growth is still fresh and comes off easily, most leaves are down, and the wall can dry before freezing nights. Skip very cold days, when water left in seams and on walkways can freeze.
On Long Island and in Westchester, many homeowners plan the siding wash together with the last gutter cleaning of the season. Spring, after the last frost, is the other good window.
08. How to slow the green from coming back
No wash lasts forever, but a few habits slow the growth:
- Trim shrubs back so air can move between the plants and the wall.
- Turn sprinkler heads so they water the lawn, not the siding.
- Keep gutters clear and downspouts attached, so water does not pour down the wall.
- Pull mulch and soil back from the bottom row of panels.
The roof and deck often need attention at the same time. Black streaks on shingles need their own method, explained on our roof washing page, and a green, slippery deck is handled with deck and fence washing. For the ground around the house, our guide to driveway oil stains on concrete and pavers and the older post on how often to power wash a driveway cover the rest.
09. What the damp season brings inside
The wet leaves, mud and pollen that coat the siding also get tracked onto entry rugs and hallway carpet. This October our crews picked up and cleaned area rugs from homes in Wantagh and Rye, and fall is when many families book an indoor cleaning before the holidays.
If you are already scheduling a house wash, our carpet cleaning service can be booked for the same week, with non-toxic products safe for kids and pets. Most carpets are ready to walk on in 4 to 6 hours.
10. Siding washing in your area
On Long Island we serve homes across the Nassau County service area, including house washing in Garden City and power washing in Freeport near the canals, and across Suffolk County, including Huntington power washing.
North of the city, our Westchester County service area includes siding and power washing in Scarsdale and nearby towns. In the city, we serve detached and two-family homes in Forest Hills and offer pressure washing in Riverdale in the Bronx.
Most areas can be scheduled same-day or next-day. Every job starts with a free quote, the price is confirmed with you before any work begins, and you pay by card or cash when the job is done. Call 1-800-589-4364 or use the form below and tell us how many stories the house has and which sides are green.
Green siding and mildew: common questions
Is it safe to power wash vinyl siding?
It can be, but high pressure is the wrong tool for most vinyl siding. A low-pressure soft wash cleans the wall without forcing water behind the panels. Some siding makers do not want pressure washers used on their products at all.
Why does the north side of my house turn green?
It gets the least sun, so dew and rain stay on it the longest. Algae and mildew grow on the damp dirt and pollen, especially behind shrubs.
Can I use bleach on vinyl siding?
Not undiluted. The Vinyl Siding Institute warns against cleaners with undiluted chlorine bleach. Use a mild cleaner, test a small spot and rinse well.
How often should vinyl siding be washed?
Most houses look good with a wash every year or two. Shady walls, homes near the water and houses surrounded by trees may need the north side done every year.
When is the best time of year to wash siding?
Spring after the last frost, or fall before the first freeze.
Ready for clean, bright siding again?
Get a free quote for siding washing and save 10% on your first cleaning.
Get your free quote → Call 1-800-589-4364