Roof Algae & Cold Weather: Yes, It Still Grows

Ruan Marinho • February 10, 2026

When the trees have all shed their leaves and perennials have gone dormant, it's hard to believe that something as small and insignificant-looking as algae is still growing. Algae might look fragile but it's really pretty tough. Just ask anyone who has had to have it soft washed off their roof!

Why Winter Algae?

Soft washing is an exterior cleaning method that uses low‑pressure water combined with specially formulated cleaning solutions to remove grime and biological growth. Unlike high‑pressure power washing — which can strip granules, damage shingles, and void roof warranties — soft washing relies on the cleaning agents to break down contaminants and rinses them away gently. This makes it ideal for roofs, siding, decks, and other delicate exterior surfaces. That blue-green micro-organism leaving nasty-looking dark streaks on your roof is Gloeocapsa magma. This algae-like cyanobacterium has no problem adapting to winter weather — in fact, it may actually grow better in colder weather!


  • It prefers shady areas so weaker winter sunshine is no problem for it.
  • It needs moisture to thrive. Even though humidity may be lower in winter, the ample precipitation more than makes up for it.
  • It feeds on the limestone particles in shingles so there's no lack of winter feed for this pest. 
  • It also produces a tough outer sheath for protection from UV rays. That durable sheath helps it survive by providing protection against harsh weather and drastic temperature changes.


Think surviving a Pennsylvania winter is tough? These cyanobacteria survived a trip to space! Coastal rocks containing many types of microorganisms (including Gloeocapsa magma) spent 553 days attached to the outside of the International Space Station. Guess which organism survived?

Dealing with Roof Algae

So, what can you do about roof algae in winter? If the weather is temperate (above 40°) your roof can be soft washed to remove it. Otherwise, you'll probably have to wait until March or so before it can be removed via soft washing. And soft washing really is the best way to deal with this unsightly (and rugged!) little pest.

Call Us for Help Cleaning Your Roof

At Maintain It All, our technicians are experts at dealing with Gloeocapsa magma. After all, we've been successfully removing it from customers' roofs since 2009 and have 400 5-star reviews to prove it. Contact us to learn more or to request your free estimate.