The most common answer Londoners give to the question of when they clean their windows is “when they look dirty.” The second most common answer is “not recently.” Both responses share the same underlying assumption: that window cleaning is a reactive task, triggered by visible deterioration, and that the glass is essentially passive in the intervals between cleans. Neither assumption holds up. London’s windows are subject to a continuous and seasonally variable accumulation process driven by pollution, moisture, biological matter, and atmospheric chemistry – and what is happening to the glass in any given month is often quite different from what happened the month before. This guide works through the year season by season, explaining what each one actually does to glass, when cleaning delivers the most value, and why the apparently sensible strategy of waiting for good weather is, in this city, a more complicated proposition than it first appears.
What London Weather Is Actually Doing To Your Glass
Before the seasonal breakdown, it is worth establishing a principle that the rest of the guide depends on: glass contamination in London is not episodic. It is continuous. Every day that a window sits unclean, the existing deposit layer is doing two things simultaneously – attracting new particles through electrostatic and adhesive bonding, and being chemically acted upon by atmospheric moisture, pollutants, and UV radiation in ways that progressively integrate those deposits with the glass surface. The practical consequence is that the longer contamination remains on glass, the harder it becomes to remove and the more likely it is to leave permanent surface changes. This is not an argument for cleaning windows every week. It is an argument for understanding that the relationship between cleaning frequency and cleaning difficulty is not linear – a window left for twelve months is not merely twice as difficult to clean as one left for six. It is often considerably more than that.
Spring – The Season That Looks Like An Opportunity And Mostly Is
The Post-Winter Reckoning
Spring is the window cleaning season that most Londoners actually think about, and the instinct is not wrong. Winter deposits a specific and unpleasant mixture onto glass: traffic particulates released in higher concentrations by cold-start engines, coal and wood smoke from the city’s chimneys and fireplaces, condensation cycling that has been mineralising hard water deposits layer by layer since October, and the general organic grey film that accumulates during months of short, low-light days when nobody wants to look too closely. A spring clean addresses all of this and does so at the right moment – before the new growing season adds its own contributions.
The Pollen Complication
The complication with spring in London is pollen. The city’s urban tree canopy – one of the densest of any major European city – releases significant volumes of pollen from February onwards, with plane trees, birches, and oaks contributing successive waves through to June. Pollen is not merely a cosmetic nuisance on glass. It is sticky, it traps other particles, and when wet it releases organic acids that etch into glass surfaces over time. The practical implication is timing: a spring clean carried out in early March, before the main pollen season establishes, will stay cleaner for longer than one carried out in late April. It is also worth noting that tree resin – released by London planes and other species throughout spring – is significantly harder to remove from glass than pollen and requires solvent action rather than standard cleaning products. Clean before the trees get going, and the spring window stays manageable.
Summer – The Season That Rewards Effort
Summer is the window cleaner’s preferred season, and not simply because of the weather. Clean glass stays cleaner for longer in summer than at any other time of year, for several converging reasons. Lower rainfall means fewer wet-dry mineral deposit cycles. Higher evaporation rates mean that cleaning solution dries quickly and evenly, reducing streaking. Longer daylight hours mean both that cleaning is easier to assess and that the results are more visible and more appreciated.
The one summer-specific risk worth understanding is UV-related calcification. Extended exposure to direct summer sunlight accelerates the bonding of calcium carbonate deposits and certain organic residues to the glass surface – a process that is negligible over a few weeks but meaningful over a full summer. Windows that enter summer with existing hard water deposits or organic contamination and are left unaddressed until autumn will present a notably harder cleaning job in September than they would have in May. The lesson is not to clean more frequently during summer, but to start summer with clean glass rather than carrying spring’s residue into the UV-intensive months.
Autumn – The Quietly Damaging Season
Autumn is the season most homeowners overlook from a window maintenance perspective, and it is the one that arguably deserves the most attention. The specific autumn contributions to glass contamination in London are several, and none of them are immediately obvious.
Falling leaves deposit tannins onto any surface they contact, including glass. Tannins are organic acids that stain glass and become progressively harder to remove as they dry and oxidise. London’s abundant street trees – planes, limes, chestnuts – shed substantial volumes of leaf matter directly adjacent to the windows of the terraced and semi-detached houses that line most residential streets. Early autumn is also the start of the condensation season, as night-time temperatures drop while interior heating begins. Each condensation cycle deposits minerals from the residual moisture film, and the frequency of these cycles in October and November means that mineral deposit accumulation accelerates significantly compared to summer. Finally, autumn pollution levels in London tend to rise as domestic heating increases and atmospheric conditions become less dispersive. Cleaning in early October, before condensation cycling establishes and whilst the weather is still cooperative, is one of the higher-value cleans of the year.
Winter – The Season Nobody Wants To Think About
The conventional wisdom is to skip window cleaning in winter. The weather is cold and damp, the windows will be dirty again immediately, and the whole exercise feels futile. This is understandable and mostly defensible, but it rests on a mischaracterisation of what winter is actually doing to the glass.
London winters are not particularly cold by northern European standards, but they are damp, polluted, and thermally variable in ways that are specifically unkind to glass. Domestic heating creates steep temperature gradients between interior and exterior glass surfaces, generating condensation cycles that run almost continuously from November through February. London’s air quality in winter – particularly in areas where domestic wood burning adds to traffic pollution – produces elevated concentrations of fine particulates and sulphur compounds that dissolve into condensation moisture and create a mildly acidic film on exterior glass. This film acts on calcium carbonate deposits and on the glass surface itself, accelerating the integration of mineral residue with the glass over the course of the winter months.
The practical conclusion is not that windows should be cleaned repeatedly through winter – that is genuinely impractical in London’s weather. It is that a single clean in late January or early February, timed to a dry spell of at least two days, prevents the full winter’s contamination from establishing a consolidated mineral layer before spring. One winter clean, well timed, meaningfully reduces the difficulty of the spring clean that follows.
How Often Is Often Enough?
The honest answer depends on location and exposure. Windows on the ground and first floors of terraced houses facing busy London roads accumulate contamination significantly faster than those in quieter residential streets or in properties set back from traffic. Basement windows with limited air circulation develop organic growth – algae, mould, green film – at a pace unrelated to weather season. South-facing windows are more susceptible to UV-related deposit calcification; north-facing ones to persistent organic growth from moisture retention.
As a working framework, most London homes are well served by four cleans per year – once in early spring before the pollen season, once in early summer to start the high-visibility months cleanly, once in early autumn before condensation cycles establish, and once in late winter to break up the mineral accumulation before spring. For properties on heavily trafficked roads, two to three monthly cleans during the higher-accumulation months of autumn and winter will prevent the progressive bonding that makes annual or biannual cleaning so laborious. The economics of more frequent, lighter cleans versus less frequent, heavier ones consistently favour the former – both in cleaning effort and in long-term glass condition.
The Actual Answer
There is no universally correct window cleaning schedule, but there is a universally correct principle: clean before deposits establish rather than after they have. London’s environmental conditions – the hard water, the urban pollution, the biological contributions of one of Europe’s greenest capital cities, the relentless thermal cycling of its damp, mild winters – mean that glass left to its own devices moves through a predictable deterioration cycle that is far easier and cheaper to interrupt early than to reverse late. The seasons are not equally demanding on glass, and understanding what each one contributes is the most useful thing a London homeowner can take from this guide.
