How Often Should You Pressure Wash Your Home in Missouri?

If you live in Missouri, you've probably noticed that your home's exterior can go from clean to green surprisingly fast. Between the humid summers, heavy spring pollen, and the freeze-thaw cycles of winter, home exteriors in St. Charles County and St. Louis County take a real beating. So how often should you actually be washing your house?

The Short Answer: Once or Twice a Year

For most Missouri homeowners, washing your home's exterior once a year is the minimum — and twice a year is ideal if you have significant shade, mature trees nearby, or have noticed algae and mold building up quickly on your siding.

Missouri's climate sits in a humid continental zone, which means warm, wet summers and cold winters. That combination is perfect for the growth of algae, mold, mildew and the black-streaking bacteria called Gloeocapsa magma that you see creeping across siding and rooftops across the region.

Why Missouri Is Harder on Homes

Compared to drier states, Missouri homes need more frequent cleaning for a few specific reasons:

High humidity — Missouri summers average 70%+ relative humidity, which is prime growing conditions for algae and mildew on any shaded exterior surface
Tree canopy — The St. Peters, O'Fallon and Chesterfield areas have mature tree coverage that keeps north and east-facing siding shaded and damp for hours after rain
Pollen season — Spring pollen from oak, maple and elm trees coats every outdoor surface and stains concrete and siding if not removed
Road salt — Winter road treatment leaves salt residue on driveways and lower siding that accelerates deterioration if left untreated

Best Times of Year to Wash in Missouri

Spring (April–May) is the most popular time — after the last freeze, before peak summer heat. You're removing winter grime, salt residue and the first wave of pollen. This is also the best time to clean and seal your driveway before summer heat sets the stains in.

Fall (September–October) is the second best window — after summer algae growth peaks and before winter sets in. A fall cleaning removes biological growth before it has all winter to penetrate surfaces and cause damage.

Pro tip: If you can only wash once a year, choose spring. You'll remove winter damage, kill algae before it spreads in summer heat, and your home will look its best during the high-curb-appeal season when neighbors are outside and buyers are shopping.

Signs You Need to Wash Sooner

Don't wait for the calendar if you notice any of these on your home:

Green or black streaks on siding, brick or stucco
Visible mold or mildew growth on north-facing walls
Driveway turning green from algae — especially in shaded areas
Dark staining on roof shingles spreading downward
Gutters with green streaking down the face

These are signs that biological growth has taken hold and is actively damaging your surfaces. The sooner you address it, the less damage occurs and the easier it is to clean.

What About Driveways and Roofs?

Different surfaces have different schedules. Concrete driveways can often go 2–3 years between cleanings if sealed properly after each wash. Roofs should be evaluated annually and cleaned when black streaking appears — typically every 2–3 years for most Missouri homes, more frequently in heavily shaded areas.

Decks and fences usually need annual attention at minimum, especially wood surfaces that absorb moisture and support mold growth quickly in Missouri's climate.