Pollen Season and Your Siding

When it actually happens here

Tree pollen in eastern Massachusetts starts rising in March and generally peaks through April and May. It does not arrive all at once, and it is not one tree.

Allergists describing the New England sequence put maple, birch and ash first, then oak, then pine later, into late May and June. That sequence is why the season feels longer than people expect and why there is often a second wave just as you thought it was over.

It also varies a lot year to year with the weather. In 2026 a cool May held the trees back and then a warm spell released everything at once, which is the kind of season where surfaces go from clean to coated in about a week.

The pine wave is the one you see

Most tree pollen is invisible on a surface. The one everyone notices is pine, because the grains are large enough and numerous enough to settle as a visible yellow film on siding, decks, cars and outdoor furniture.

That is worth knowing for timing. If you wash in mid April you have cleaned off the pollen you cannot see and you are still ahead of the pine, which means you may be washing twice.

For most properties the useful window is after the pine has finished rather than in the middle of it.

Where it sits worst, and why

The same surfaces that hold everything else hold this: north facing walls, shaded elevations, anything under tree cover, and horizontal surfaces such as deck boards, railings and window sills where it can settle rather than run off.

The common factor is drying time. A sunny south wall sheds a film of pollen in a couple of rain showers. A shaded north wall stays damp, and damp pollen does not rinse, it sticks.

Textured surfaces make it worse again. Pollen settles into the grain of a wood deck and the profile of vinyl siding in a way that a hose does not reach.

What happens if you leave it, honestly

We are not going to tell you pollen eats your siding, because we have no source that says it does and we do not believe it.

What it does do is sit in a damp organic film on a shaded surface, and a damp organic film is what mildew and algae grow in. Left through a wet summer on a north wall, what started as a yellow dusting becomes the grey green staining that actually needs work to remove.

So the case for washing it off is not that pollen is corrosive. It is that leaving it gives something else somewhere to start, and that the longer it sits the less a simple wash will take it off.

Why it matters more before painting

This is the one place where pollen moves from cosmetic to consequential. Paint needs to bond to the substrate, not to a layer of dust sitting on top of it.

A heavy pollen year during the exterior painting season is a genuine complication, because a surface can be prepped in the morning and lightly coated again by the afternoon. Washing is not an optional first step in that situation, and the gap between washing and coating matters.

It is the main reason our own exterior painting work follows a wash rather than skipping it. Coating over a pollen film is a cheaper job today and a shorter lived one.

How it gets washed

The same rule as everywhere else on this site applies: match the pressure to the surface. Vinyl, wood and masonry each want different handling, and a deck board is not a driveway.

Pollen is generally not a difficult soil. It has not bonded to anything and it comes off with the right solution and a sensible rinse. The difficulty appears when it has been left long enough to become a mildew problem, at which point you are cleaning the thing that grew in it rather than the pollen.

Which is the practical argument for doing it in June rather than September.