If your roof or siding has turned green over time, you might be growing the laziest garden ever: a mix of algae and mold! Green growth on your roof or siding can cause damage to your home and hurt your curb appeal. But can you tell whether it’s algae or mold?
Algae vs. mold: what’s the difference?
Algae and mold are often confused because they’re both green in color. But they are actually quite different from each other! The biggest distinction, byjus.com explains, is how they receive their nutrition. “Algae are autotrophic. They have chlorophyll and perform photosynthesis. Fungi are heterotrophic, they are dependent on others for their nutrients requirement. They feed on dead and decaying organic matter.” This helpful chart lists the characteristics that algae and mold have and how they differ.

Before After
Growth prevention
Now, we know what you’re thinking. “Why does it matter whether the green stuff on my house is algae or mold? It’s green and gross and needs to go!” Well, knowing what is causing that “green stuff” to grow can help you with prevention! If you’re constantly just dealing with the symptoms, you’ll never get to the root of the problem and it’ll just grow back. Some of the things that cause green growth on your home include:
- Moisture
- Warmth
- Dirt
- Shade
A gentle soft wash paired with a soap mixture can typically get rid of any discoloration and restore your roof or siding to its original color. But if you notice something green growing on your home, it could be an indication of a deeper problem. For example, if you determine there’s mold growing on your roof, it’s probably a leak or improper drainage issue and fixing it right away is the solution. On the other hand, if dirt or shade is to blame, cleaning those surfaces on a regular basis is the best prevention strategy.