How to Remove Algae
from Stucco

Algae on stucco is one of the most common complaints we hear from homeowners across Southern California — and for good reason. Southern California's climate is practically a perfect incubator for the stuff. Warm temperatures, morning moisture from the marine layer, irrigation overspray, and shade from trees all contribute to algae establishing itself on home exteriors.

The good news? It's removable. The important caveat? How you remove it matters a lot. Do it wrong and you risk damaging your stucco, which is a much more expensive problem than the algae itself.

First: Identify What You're Dealing With

Not all discoloration on stucco is the same, and knowing what you're looking at helps you understand the right treatment:

• Black streaks running from the roofline down: Almost certainly Gloeocapsa Magma — a cyanobacteria (commonly called algae) that washes down from roof shingles during rain
• Green patches, especially in shaded areas: Green algae or moss — common near downspouts, under eaves, and on north-facing walls
• Fuzzy or slimy texture: Moss, which tends to grow in very moist or shaded spots
• Dark gray or black patches: Could be mold or mildew, particularly in areas with poor airflow

All of these respond well to the same treatment approach — the difference is mainly in how established the growth is and how long the dwell time needs to be.

What NOT to Do

Before we get to the solution, let's quickly cover the common mistakes that end up making things worse:

• Don't use bleach directly on stucco — undiluted bleach can discolor and degrade stucco over time and will damage nearby plants
• Don't scrub vigorously with brushes — this can damage the stucco texture, especially on older or more delicate finishes
• Don't ignore it and hope it goes away — algae spreads, and the longer it's there, the more established it becomes and the harder it is to remove

The Right Method: Soft Washing

The professional standard for removing algae from stucco is soft washing — and there's a clear reason it's the preferred method among exterior cleaning professionals. It works better, lasts longer, and causes zero damage to your stucco when done correctly.

Here's how the process works:

Step 1: Pre-Wet Landscaping

Before any cleaning solution is applied, we thoroughly wet all nearby plants, lawn and landscaping. This dilutes any solution that might drift or drip onto plants, protecting them from the cleaning chemistry.

Step 2: Apply Cleaning Solution

A professional soft-wash solution — typically a diluted sodium hypochlorite mixture with surfactants and algaecides — is applied to the stucco surface at low pressure. The surfactants help the solution cling to vertical surfaces and penetrate into the algae colony.

Step 3: Dwell Time

The solution is allowed to sit on the surface for a period — usually 10–20 minutes depending on the severity of the growth. During this time, the active ingredients are killing the algae, mold and mildew at the root level. This is the key step that separates soft washing from simple rinsing.

Step 4: Gentle Rinse

The surface is rinsed with low-pressure water to wash away the dead growth and cleaning solution. Landscaping is rinsed again as a final precaution.

Step 5: Inspection

We inspect the full surface to ensure even, complete coverage. Any areas that need additional treatment get a second pass.

Can I DIY This?

Technically yes — but there are real risks if you don't know what you're doing. The main concerns with DIY algae removal on stucco:

• Using too high a concentration of cleaning solution can damage or discolor stucco
• Using too low a concentration means the algae isn't fully killed and regrows quickly
• Improper application can cause streaking or uneven cleaning
• Working on ladders or scaffolding for multi-story homes is genuinely dangerous
• Without professional equipment, you may not achieve the coverage and dwell time needed for full effectiveness

For a small, single-story area that's easy to access, a careful DIY approach is possible. For the full home exterior, calling a professional is going to give you better results, faster, and without the risk of causing damage.

Preventing Algae from Coming Back

While you can't completely prevent algae growth in Southern California's climate, you can slow it down:

• Adjust irrigation heads so they're not spraying directly onto your stucco
• Trim back trees and shrubs that shade your home's walls — more sunlight means less algae
• Clean gutters regularly so they're not overflowing and keeping your walls wet
• Consider a periodic preventive soft wash treatment before the growth becomes visible

Ready for a Clean Home?

If your stucco is showing algae growth — whether it's been there for six months or six years — we can help. We serve homeowners throughout Southern California and would be happy to give you a free, no-pressure quote. The results consistently make our customers very happy.