A soft wash removes what is growing on your home today. It cannot stop new spores from landing tomorrow, so how long the result lasts depends on your property more than on the wash. Here is what speeds regrowth up, what slows it down and how to tell when it is time to book again.
In This Article
What a soft wash buys you, and what it cannot
Soft washing applies a cleaning mix at low pressure, lets it work for the time the product label allows, then rinses the loosened film away. It kills the algae, mould and mildew that are already on the surface.
It does not vaccinate the wall. Spores travel on the wind all year, so a clean surface is a fresh start, not a shield. The next colony still needs moisture, a thin layer of organic film to feed on and some warmth. How quickly your house supplies those three things is the real answer to "how long does it last?"
The size of the reset matters as well. A light green tint is quick to treat, and the clean result holds well because there is little left behind. Heavy buildup, especially crusty lichen, may take more than one visit to clear and may leave faint shadows that fade slowly.
Treat the wash as a reset. A promise of a fixed number of years is a guess about your trees, your shade and next summer's weather.
Why the north wall greens up first
Shade and slow drying matter more than the siding material. A wall that stays damp after rain grows algae sooner than one that dries within an hour of sunshine.
| Spot on the property | Effect on how long the result lasts |
|---|---|
| North wall behind a hedge or fence | Shortest. Little sun, poor airflow, long drying times. |
| Wall under a mature maple or oak | Shorter. Pollen, sap and leaf litter feed the film. |
| Wall beside a downspout or sprinkler | Shorter. Repeated splashing keeps the surface wet. |
| Under eaves and porch ceilings | Mixed. Rain never rinses these areas, so dust settles and humidity lingers. |
| Open south or west wall | Longest. Sun and wind dry it fast. |
Texture plays a part too. Smooth vinyl tends to release growth more easily than rough stucco or porous brick, which hold moisture and spores in their pores. Roofs follow the same logic: a north-facing slope shaded by the neighbour's house usually darkens before a slope that bakes all afternoon.
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A realistic year in Southern Ontario
Growth follows moisture and warmth, so the weather matters more than the calendar.
- Spring: thaw and rain wake dormant colonies. Pollen and maple seed pods settle on the walls and give the film something to eat.
- Summer: humid weeks with heavy morning dew are the fastest-growing stretch. A wet July can undo more than a dry one.
- Fall: wet leaves and cool nights keep shaded walls damp, but growth slows as temperatures drop.
- Winter: freezing weather pauses things. A wall washed in early fall often looks clean through the cold months, then gets its real test when warm, wet weather returns.
That last point is why "it still looks great in February" says little about how it will look next August.
Habits that stretch the result
You cannot control the spores. You can control how easily they settle in.
- Keep eavestroughs and downspouts flowing so overflow does not run down the walls.
- Point sprinklers at the lawn, not the siding.
- Trim shrubs and low branches so the shady side gets light and moving air.
- Keep mulch and soil below the bottom edge of the siding, and sweep leaves out of corners where they sit against the wall.
- Walk the house each spring and fall with the visual inspection guide in hand.
How to tell it is time to book again
Skip the fixed calendar and watch for triggers: a green tint creeping back across the shadiest wall, dark specks on trim and soffits, or streaks showing on the roof from the driveway. Catching regrowth while it is thin is easier than waiting until crusty lichen or moss has settled in.
A good crew that has looked at your shade, your trees and your siding can tell you which walls to watch first. Ask them, and write it down with the date so you can compare next year.
Frequency also depends on your siding and lot. Our year-round planner shows how to fit checks into the seasons.
When you do want a price, soft washing from D&D starts at $350 for typical Kitchener-Waterloo homes. The quote is free and confirmed in writing before any work begins, and it reflects how heavy the growth is, not just the size of the house.
Key Takeaways
- A soft wash removes existing growth but does not stop new spores, so the result lasts as long as your site keeps the surface dry.
- Shaded north walls, tree-drip zones and areas near downspouts or sprinklers regrow first.
- Growth slows in freezing weather, so a wall that looks clean in winter is not proof of how it will look after a humid summer.
- Watch for early regrowth and book when it is thin, not when lichen or moss has taken hold.
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