1976 still holds the record, and that is not the comfort it sounds like

This site stores the daily temperature record back to 1950 for every town on it, and one of the things it counts is the longest unbroken run of days above 25 degrees in each year.

Run that over seventy five years and something odd comes out. In 19 of the 25 towns, the longest run ever recorded is still 1976.

Cambridge managed 17 consecutive days that summer. London, Reading, Oxford and Leicester each managed 16. Bristol, Birmingham, Portsmouth and Southampton managed 14. Half a century has passed and none of it has been beaten.

Six towns have their record somewhere else, and four of those are places where a record spell is only two or three days in the first place: Edinburgh in 1955, Belfast in 2018, Dundee and Newcastle in 2022. Perth’s is five days in 1975, the summer immediately before the famous one. Norwich is the single real exception, with seven days in 2006.

The record is not the thing that changed

It would be easy to stop there, and a certain kind of column does.

The average tells a different story from the record, and the average is the one that describes what a summer is actually like.

Take the longest spell in each year and average it across the years. For London that figure was 2.8 days for 1951 to 1979. For 2010 to 2025 it is 5.1. Reading went from 2.6 to 5.1, Cambridge from 2.8 to 5.1, Portsmouth from 1.7 to 4.0, Norwich from 1.3 to 3.4, Birmingham from 1.6 to 3.4.

In round terms, the longest hot spell of a typical southern summer has doubled, and it has doubled without ever once going near 1976.

That is not a contradiction. It is what a rising average with a fat old outlier on top of it looks like. 1976 was extraordinary in 1976 and it would be unremarkable as a decade in which it happened rather than a fluke within one. The mean daily maximum in these towns is rising at between 0.13 and 0.25 degrees a decade, and the number of hot days a year has multiplied several times over. The spell record simply has not been the thing to give way yet.

Why a garden cares about the run and not the day

A single hot day is a nuisance. A run is a different problem, and the reason is that soil holds water.

Ground that was watered, or rained on, three days ago still has a reserve. One hot day draws that reserve down. The plant transpires harder because the air is drier and warmer, the roots pull harder to keep up, and the store absorbs it.

Six days in a row is arithmetic going the wrong way every day. The store is being drawn down faster than anything is putting it back, and at some point the plant stops keeping up, closes its stomata, stops growing, and starts losing leaves it cannot afford to lose. Nothing about the sixth day is worse than the first. The reserve is just gone.

This is why the doubling matters more than the record. A two day spell is inside what most established planting can ride out. A five day spell, arriving most years now rather than occasionally, is not.

What follows from that

Water less often and much more deeply. A daily sprinkle wets the top centimetre, which evaporates, and trains roots to stay near the surface where the next hot day will find them. A thorough soak twice a week puts water where deep roots can reach it and encourages them to go there.

Mulch is the cheapest thing on this list. A layer of compost, bark or even grass clippings over damp soil slows evaporation from the surface, which is where most of the loss happens. Apply it to soil that is already wet, not to dry ground.

Containers are the emergency, not the borders. A pot has a small volume, no connection to the water table, and sides exposed to the sun on three dimensions. Established shrubs in the ground will usually survive a spell that kills everything in a container. Group pots together, move them into afternoon shade, and accept that in a long spell they need water daily.

Let the lawn go brown. It is dormant, not dead, and it greens up within a fortnight of proper rain. Watering a lawn through a hot spell uses an enormous volume of water to keep something alive that was not in danger.

Plant for the spell you now get, not the one you used to. The tender end of what survives a British winter has been widening for years and gets the attention. The change that will actually cost you plants is at the other end, in what tolerates a dry fortnight in July. Deep rooted, silver leaved, and Mediterranean in habit is not a fashion, it is a hedge against the average that moved.

The honest caveat

These are grid cell figures, an average over roughly eleven kilometres, so they read a little below what a single station in the same town records on the same day. That flattens the peaks and it means the spell counts here are, if anything, conservative.

The comparison between decades is the reliable part, because the same method and the same model are applied to every year in the series. Whatever the absolute numbers are doing, 1951 to 1979 and 2010 to 2025 were measured the same way.