Property Care · Lexington, KY
Algae, Mold & Mildew on Lexington Properties: Why It Keeps Coming Back
From roof streaks to green film on siding, decks, and patios, algae and mildew grow faster in Lexington than in most
parts of the country. Here’s why it happens, when it’s worst, and which surfaces are affected most.
If you’ve noticed dark streaks creeping across your roof, green film building up on your siding, or algae taking hold on your deck or patio,
you’re not imagining it getting worse every year. Lexington’s climate is one of the more favorable environments in the country for algae, mold,
and mildew to grow on exterior surfaces. Understanding why explains a lot about when it shows up and how fast it comes back.
Why This Happens Here
Lexington sits in a humid subtropical climate with no true dry season. The National Weather Service’s 30-year climate normals show the region
gets close to 50 inches of rain a year, spread across every month instead of concentrated in one wet season. Spring is the wettest stretch,
averaging over 14 inches between March and May, with May alone bringing close to 4 inches. Summer isn’t far behind, averaging nearly 14 inches from June through August. That’s also when temperatures climb into the mid 70s and 80s.
Warm temperatures plus consistent moisture is exactly what algae and mold need to establish themselves on a roof, a fence, or a shaded patio.
Fall is the driest season here. Organic growth tends to slow down heading into October and November, though it never fully disappears given how little the region actually dries out.
Shade makes all of this worse. A north facing roof slope, a fence line under mature trees, or a deck tucked under tree cover holds onto moisture long after the rest of the property has dried out. Two homes on the same street can age at completely different rates depending on how much sun each one actually gets.
When It’s Worst in Lexington
There isn’t one single “algae season” here the way there might be in a drier climate. But the risk isn’t flat across the year either.
Late spring through summer is when conditions line up most consistently. Warm air, high humidity, and the season’s heaviest rainfall combine to give algae and mold everything they need at once. This is also when tree pollen gives way to grass pollen season, and that thin pollen film settling on siding and patios acts almost like a coating, holding moisture against the surface a little longer than bare siding would.
Fall’s lower rainfall gives surfaces more of a chance to dry between rain events, so growth visibly slows. Winter doesn’t stop things outright either. Lexington’s average first freeze has been trending later, now typically arriving in late October or early November based on the most recent 30 year data.
The region doesn’t hold a hard freeze consistently until well into the season. Between rain, morning dew, and temperatures swinging above and below freezing through the winter, shaded and damp surfaces can still hold onto the moisture that keeps organic growth alive, even if it’s not actively spreading the way it does in July.
What It Affects
Roofs
Roofs are usually the first place people notice it. The dark streaks on asphalt shingles are often Gloeocapsa magma, an algae that thrives in the same warm, humid conditions Lexington sees most of the year. It spreads fastest on north facing slopes and roofs sitting under heavy tree cover, since those areas hold moisture longest after a rain. Left alone, it can also encourage moss and lichen in the same shaded spots.
Siding
Siding picks up the same organic growth, especially vinyl and painted surfaces on the shaded side of a house. It usually shows up as a green or black tint near the bottom of the siding or in corners with poor airflow.
Decks & Fences
Decks and fences are especially exposed since they’re horizontal or low to the ground and often sit near landscaping that holds moisture. We’ve seen this firsthand on backyard decks around Tates Creek and the Hamburg area, and on wood fencing along Old Frankfort Pike. Mature trees provide shade but also keep the wood damp longer than it should be. Algae and mildew can work into wood grain itself rather than just sitting on the surface, so wood needs more attention than composite or vinyl.
Patios & Concrete
Patios and concrete get it too, usually as a slippery green film in shaded corners or along edges where grass or mulch keeps the concrete from fully drying out. This is as much a safety issue as an appearance one, since wet algae on a walking surface gets slick fast.
Why Some Spots Come Back Faster
If you’ve ever had one section of your property cleaned and noticed algae creeping back there first, that’s not a fluke.
Shade and airflow are the biggest factors. A roof slope, deck, or fence line under tree cover or tucked against a house stays damp for hours after a sunny, open section has already dried out. Less direct sun means slower drying after every rain, and less air movement means humid air sits against the surface longer.
Standing moisture nearby plays a role too. Mulch beds, dense ground cover, or sprinkler overspray near a patio, deck, or the base of siding keep the surrounding air more humid than the rest of the property, even after the ground looks dry.
These are landscaping realities more than problems to fix outright. Knowing which spots run damper than others just helps set realistic expectations for how often each part of a property needs attention.
Ready to Deal with Algae, Mold, or Mildew on Your Property?
Whether it’s black streaks on the roof, green film creeping across your siding, or algae making a deck or patio slippery, the fix depends on the surface and how far the growth has spread. We inspect the affected areas first, then match the cleaning method, soft washing for delicate surfaces like roofs, siding, decks, and fences, and pressure washing for concrete and patios, to what will actually clean it without causing damage.