Plant for next summer this month, and leave the silver-leaved plants until spring

A garden planted in the 1990s was planted for summers that no longer happen.

That is not a figure of speech. This site stores the daily temperature record back to 1950 for twenty five British towns, and one of the numbers it counts each year is the longest unbroken run of days above 25 degrees. That run is what a border actually has to survive. A single hot afternoon costs a plant very little. A week of them with no rain is what kills it.

The longest hot run has grown by three quarters

Average of each year’s longest run of consecutive days above 25C, with the count of days reaching 28C alongside it. The 2020s figures cover the six complete years from 2020 to 2025.

Across all twenty five towns the average longest run went from 2.1 days in the 1990s to 3.7 this decade. Southampton, Bristol and Cardiff more than doubled. And 2026 is not in those figures at all, because the year is not complete: with the series stored to 24 July, London had already had a run of fifteen.

Your own town is in the full series by town. If you want the longer view, what 77 years of daily readings say about British summers goes back to 1950, and 1976 still holds the record explains why the peak matters less than how often the long spells now come.

The window is now, not October

Spring feels like planting season. For the plants that have to get through a long dry run, it is usually the wrong half of the year.

The RHS, in its drought resistant gardening advice, gives two windows: March, as the soil warms up, or September, when the soil is still warm and there is time for plenty of root growth before winter. A plant that goes in this month has the whole of the autumn and the winter wet to get its roots down before it meets its first summer. A plant that goes in next May meets July with the roots it arrived with.

That makes the next three weeks the useful ones for hardy trees, shrubs and perennials.

The plants to leave until spring

This is the part that runs against instinct.

The plants most people reach for when they think of drought are the Mediterranean ones: silver and grey leaved, sun loving, the kind that look at home in gravel. The RHS notes that many drought tolerant plants have silver or grey-green leaves because the pale colour reflects the sun, and that fine hairs on some of them trap moisture.

Those are exactly the plants it advises against planting in autumn. Its advice is to plant Mediterranean style, silver leaved plants in spring, so that they establish in warmer weather. The less hardy ones in that group do not want to spend their first winter in cold wet soil with no roots to speak of.

So the honest plan for a garden that is going to face hotter summers is split across two seasons: the hardy structure now, the silver-leaved sun lovers in spring.

Plant small, and skip the fertiliser

Two pieces of RHS advice matter more for heat than they seem.

Buy small. The RHS suggests perennials in 9cm pots and small trees and shrubs where you can get them. A small plant settles into its own soil as it grows, rather than trying to support a large top on a root ball that was grown in a nursery.

Organic matter, not fertiliser. Dig in organic matter before planting, which improves both how much water the soil holds and how well it drains. Do not add fertiliser. It pushes soft, lush growth that flops in summer and needs more watering, which is the opposite of what a plant facing a six day hot spell needs.

The first year decides it

“Drought tolerant” describes an established plant. It does not describe one that went in last month.

The RHS is explicit: water newly planted trees, shrubs and perennials regularly in their first year, even if they are sold as drought tolerant, and large trees for up to three years. Its guidance on watering is to water less often but more thoroughly, so the soil is moist 15cm down, then let the surface dry before watering again. Deep, occasional watering is what trains roots to go down, and down is where the water still is in August.

Established trees, shrubs and perennials, on the same guidance, only need watering in extreme drought. That is the payoff for getting the first year right.

Mulch in winter, not in the heatwave

The mulch that helps in July goes on in winter. The RHS defines a mulch as a layer at least 5cm thick, applied from late autumn to late winter, roughly November to February. It holds moisture in the soil through summer and lets rain in during the wet months. Around Mediterranean style planting, it suggests 5 to 7.5cm of gravel instead.

A mulch laid on dry soil in the middle of a hot spell mostly keeps the dryness in.

Do not dig up the brown lawn yet

If this summer turned the lawn the colour of straw, the temptation in September is to rip it out. The RHS says established lawns rarely need watering, and that even a lawn that has turned completely brown will green up again once rain returns.

Wait for the autumn rain before deciding it is dead. Most of the time it is not, and the effort is better spent on the borders.