What is the green growth on siding?
The green film on siding is usually algae. It is different from mildew, which shows up as gray or black spotting, and from the lichen and moss that grow on some roofs and masonry.
Identifying the growth matters because it tells a professional what they are dealing with and how stubborn it is likely to be. The common types of organic growth on Virginia homes look like this:
- Algae
- A green, sometimes powdery film, most common on shaded and north-facing walls.
- Mildew
- A surface fungus that appears as gray or black spotting, often under eaves and around trim.
- Black roof streaks
- Commonly caused by the cyanobacterium Gloeocapsa magma. These appear on roofs rather than siding.
- Lichen
- Crusty, flat patches, often gray-green, that cling tightly to masonry, wood and roofs.
- Moss
- Soft, raised green growth in damp, shaded spots, more common on roofs, walks and north-side masonry.
For help telling these apart, see our guide to black and green stains on siding.
Why does algae grow on siding in Virginia?
Algae needs moisture, and Virginia supplies plenty of it. Hot, humid summers, frequent shade and walls that stay damp after rain give algae ideal conditions, especially on the north side of a house.
- Humid summers keep surfaces damp for long periods.
- North-facing and shaded walls get little direct sun and dry slowly.
- Trees add shade and drop pollen and debris that hold moisture against the surface.
- Homes near rivers, creeks and ponds sit in damper air.
- Overflowing gutters and sprinklers keep sections of wall wet.
That is why algae is so common on homes in Stafford County, where many neighborhoods are wooded and some sit near the Potomac, the Rappahannock or Aquia Creek.
How do professionals remove algae from siding, step by step?
A typical professional algae removal follows five stages: inspect, protect, apply the solution, let it dwell, and rinse at low pressure. The details are adjusted for the siding material and how heavy the growth is.
- Inspect. Identify the growth and the siding material, and check for loose panels, damaged caulk or failing paint that call for extra care.
- Protect. Close windows, move items away from the walls, and wet down plants and shrubs so they absorb clean water rather than cleaning solution.
- Apply. Spray a diluted cleaning solution at low pressure. Many professionals work from the bottom of a wall upward during application to reduce streaking.
- Dwell. Let the solution sit long enough to break down the algae, without letting it dry on the surface. In hot sun, that often means working in smaller sections.
- Rinse. Rinse thoroughly at low pressure, usually from the top down, so the growth and solution run off cleanly. Rinse plants again afterward.
Across the industry, soft-wash solutions are commonly based on diluted sodium hypochlorite with a surfactant to help it cling. Solution strength is adjusted to the surface and the level of growth, which is one reason soft washing is best left to someone who does it regularly. This is the core of our soft washing service.
Why not just blast algae off with a pressure washer?
High pressure can knock off the visible layer of algae, but it often leaves growth behind in textured surfaces and seams, and it risks damaging the siding. Soft washing treats the growth itself.
- Blasting can crack vinyl, strip paint and force water behind siding.
- Growth left in texture, seams and pores can return sooner.
- A wand held at uneven distances leaves stripes and blotchy results.
- Upper stories are hard to reach safely with a high-pressure wand.
Vinyl is the most common case. Our article can pressure washing damage vinyl siding? covers the risks in detail.
Is algae removal safe for plants and landscaping?
With the right precautions, yes. Professionals commonly wet plants before cleaning, keep the solution at an appropriate strength, and rinse plants and soil afterward to dilute any runoff.
How long does siding stay algae-free after cleaning?
It varies with shade and moisture. Sunny walls may stay clean for a long time, while shaded, north-facing walls tend to show growth again sooner. No cleaning method permanently prevents algae in a humid climate.
Trimming branches, clearing gutters and keeping sprinklers off the siding all slow regrowth. For most homes, a yearly wash keeps algae from getting established. See how often you should pressure wash your house in Virginia for the factors that change that schedule.
How Ultimate Powerwash removes algae from siding
Ultimate Powerwash removes algae from siding with low-pressure soft washing, adjusted to the siding material and how much growth there is. We look at the material and its condition before choosing a method.
We are based in Stafford County and have served homes and businesses since 2005, with more than 30 years of combined pressure washing experience across our team. We match the method to the surface, and algae on siding almost always calls for a soft wash as part of a full house washing service.
Our work is satisfaction guaranteed and quotes are free. We clean homes across the region, including algae removal and house washing in Fredericksburg, VA and house washing throughout Stafford, VA.
Related questions
Can I remove algae from siding with vinegar?
Sometimes, on light growth. Diluted vinegar and a soft brush can lift small patches, but it is slow on large or heavily grown walls, and the growth often returns.
Does algae damage siding?
Mostly it is a cosmetic and moisture problem. Algae holds moisture against the surface, which is more of a concern on wood trim and painted surfaces than on vinyl, and long-established growth can stain porous materials.
Why does algae come back on the same wall?
Because the conditions that grew it are still there. Shade, poor airflow and moisture on that wall let algae return; reducing those conditions slows it down.
Is the green on my siding mold?
Usually not. The green film is most often algae. Gray or black spotting is more likely mildew, a surface fungus.