Short answer
In Atlanta, pine pollen is mostly a washing problem, while mildew is a paint problem. Pollen rinses off once the trees stop shedding. Mildew has to be killed, rinsed and dried before any coat goes on, because EPA warns that paint applied over moldy surfaces is likely to peel. A few drops of bleach tell you which you have.
Why the siding turns yellow in spring and green by late summer
Two different things land on your house. In spring it is pollen: Atlanta Allergy and Asthma counted 14,801 on March 29, 2025, the highest reading in 35 years of counting and far above the old record of 9,369 from 2012. Oak, pine, sycamore, sweet gum and birch all contributed, but the yellow film on porch rails and window sills is pine.
The green and black arrive later and stay. Mildew and algae grow where siding stays damp, and Atlanta supplies both shade and water. A Georgia Tech assessment found 45.7% of the city under tree canopy in 2023, with 72% of the remaining trees on land zoned for single-family homes, and the city averages about 49.7 inches of rain a year. UGA Extension wood specialists trace the blotchy look on siding to uneven wetting by rain and dew, which is why the north wall and the side under the big oak go first.
Telling pollen, mildew, dirt and chalk apart
Find out what the stain is before you buy a cleaner. Sherwin-Williams suggests putting a few drops of household bleach on the spot. If it bleaches away, it is likely mildew. If it stays dark, it is likely dirt.
| What you see | Likely cause | What it needs |
|---|---|---|
| Yellow dust on rails, sills and the car | Pine pollen | A plain water rinse once the trees stop shedding |
| Black or gray specks that bleach away | Mildew | A mildew wash, a rinse and full drying before paint |
| Green film on the shady side or near sprinklers | Algae, often mixed with mildew | The same wash, plus fixing whatever keeps that wall wet |
| Dark streaks that do not bleach | Dirt, soot or gutter runoff | Detergent, water and a soft brush |
| White powder that rubs off on your hand | Chalking paint | A wash and an honest look at whether the coating is worn out |
Want a painter to look at your house?
Call (470) 876-1448Washing the house without stripping paint or burning the shrubs
For mildew on painted surfaces, Sherwin-Williams calls for 1 part liquid bleach to 3 parts water, left on for 10 minutes, then rinsed and allowed to dry before painting. It warns against adding detergents or ammonia, and UGA Extension gives the reason: chlorine bleach mixed with some cleaning agents can release poisonous chlorine gas. Read the label on anything you combine.
Pressure matters as much as chemistry. A narrow, high-pressure tip can drive water behind lap siding, raise the grain on soft pine trim and peel paint that was barely hanging on. Low-pressure soft washing lets the solution do the work. When we wash a house before painting, we soak the planting beds with plain water first, keep the spray off window seals and dryer vents, and rinse the plants again when we finish.
Why paint applied over mildew lets go
EPA's mold guidance is blunt: do not paint or caulk moldy surfaces, clean them and dry them first. Mildew is alive. Sealed under a new film, it keeps feeding on the dirt and moisture beneath, the bond weakens, and the dark spots show through again within a season or two.
- Kill the growth and rinse it off; scrubbing the color away is not the goal.
- Let siding and trim dry fully before primer or caulk goes on.
- Prime any bare wood exposed by scraping before the finish coats.
- Choose an exterior paint made with agents that inhibit mildew on the film, which Sherwin-Williams recommends for damp, shaded surfaces.
Scheduling a repaint around pollen season
Wet paint is sticky, and a coat applied during a heavy pollen drift dries with yellow grit locked into it. A light dusting can usually be washed off once the paint cures. A heavy one means sanding and recoating the worst walls, which is a day nobody budgeted for.
Spring is not off limits, but plan around it: wash the house right before painting rather than a week ahead, start on the side farthest from the pines, and stop when a breeze starts moving pollen across the yard. October tends to be Atlanta's driest month, one reason fall calendars for exterior painting fill early.
Cutting off the shade and water that feed mildew
Washing treats the symptom. If the same wall turns green every year, something keeps it wet.
- Branches touching the roof or siding: thin them so air moves and the wall sees some sun. Removing a healthy tree is rarely necessary.
- Shrubs pressed against the house: cut them back far enough that you could walk behind them.
- Sprinkler heads that spray the siding: turn or lower them.
- Gutters spilling over fascia and trim: clean them and extend downspouts away from the walls.
- Mulch piled against wood siding: rake it down so the bottom board can dry.
When the stain means the paint itself is worn out
A house that cleans up well after a soft wash is not necessarily due for paint. A house where mildew returns within a few months, the paint leaves heavy chalk on your hand, or bare wood shows at the sills has a coating that no longer sheds water. Washing buys time there, and a repaint that starts with the shaded walls and the trim and fascia is the actual fix. A yearly rinse after pollen season keeps either situation from getting ahead of you.