Frost is the one bit of the gardening year people plan around a date, and there isn't one. I can't tell you when the first frost will land on your garden this year, and neither can anyone else — what I can tell you is what it does when it arrives, which bits of the garden care and which don't, and one thing most people get backwards.
The mistake: it's often the thaw, not the freeze
The instinct is to think of frost as cold damage — the plant got too cold, the plant died. Quite often what actually did the damage was the morning after.
The RHS puts it plainly: "Repeated freezing and thawing, or very rapid thawing can be particularly damaging to plants", and "plants exposed to early morning sun may thaw too rapidly after a frost, causing damage to flowers and young growth". Camellias and magnolias are the classic casualties — flowers ruined by a single frost, and the ones that get hit are the ones facing the wrong way.
This turns the usual advice on its head. A plant against a sunny east-facing wall gets the first sun of the day straight onto frozen tissue. A plant in a shadier spot thaws slowly and often comes through fine. If you have something borderline and a choice of where to put it, the slow-thawing corner beats the warm-looking one.
It's also the cheapest fix in this whole article, because it costs nothing. You're not buying fleece. You're moving a pot four feet.
Where the cold actually sits in your garden
Cold air behaves like water. The RHS describes it exactly: "On frosty nights cold air forms on cooling objects such as trees, sinks to the ground and literally flows downhill to collect at low points which are known as frost pockets."
That matters more here than in a lot of the country. If your garden runs downhill and something solid crosses the bottom of it — a close-boarded fence, a thick evergreen hedge, a wall — the cold runs down and stops there. The bottom of that slope will be several degrees colder than the top on a clear night, and it will frost first and thaw last.
The fix is counterintuitive and it works: let the cold out. The RHS again — "the cold air sometimes collects behind barriers across the slope such as fences or hedges. Making gaps in the barrier can allow the air to drain away and alleviate a frost pocket." A gap at the bottom of a fence, or thinning the base of a hedge, drains the pool.
Worth knowing before you buy anything, too. The RHS hardiness rating H4 — the one that reads "hardy through most of the UK" and feels safe — carries its own exception in the small print: hardy "apart from inland valleys, at altitude and central / northerly locations". A fair few gardens round here are inland valleys. An H4 label is not a promise in a valley bottom.
What to actually do before it comes
Tender things need deciding on, not watching. The RHS timing is "at the first warning of frost, usually between September and November" — so this is a September and October job, not a November one.
Dahlias are the ones people ask me about, and the advice has genuinely changed. It used to be lift everything. Now the RHS gives you two honest options: "in milder areas of the UK and in sheltered, well-drained, parts of the garden, it may be possible to cut back the tops of tender plants, leave them in the ground and cover them with a thick mulch". Lifting is still the safer bet — their own words are that it's "safest to store the tubers inside over winter, especially if you have heavy soil".
Heavy soil is the deciding word. Plenty of gardens round here sit on clay, and clay plus a wet winter rots tubers that the cold alone would not have killed. Free-draining and sheltered, leave them and mulch them. Heavy and open, lift them. If you leave them in, expect them to start later next year.
Cannas and pelargoniums take the same decision. If in doubt, lift.
Pots are more exposed than beds. Roots in a pot are surrounded by cold air on every side, where roots in the ground have the whole earth insulating them. The RHS says as much in the hardiness scale itself — at H4, "plants in pots are more vulnerable", and at H5, "plants in pots will be at increased risk". Moving a pot against a house wall, or grouping pots together, is doing real work.
What to leave well alone
This is the part where doing less is genuinely better, and I say it to customers every autumn.
The urge is to cut the borders down to the ground and have it all neat before winter. The RHS is even-handed about it — cutting back "restores order and tidiness to the garden", but "this removes potential winter interest... plus food and habitat sources for wildlife so many gardeners delay the cut back until spring".
Two reasons to leave things standing that aren't about tidiness at all:
The stems are housing. "The dry hollow stems of perennials provide homes for insects through the winter and the seeds are vital food for birds and small mammals." Cutting everything down in October evicts the lot.
And on some plants the old growth is the frost protection. The RHS is specific: "more tender plants with woody stems, such as penstemons, are left so that the old stems protect the crown from frost. Leave pruning of these and other borderline-hardy perennials until the risk of frost has passed — usually April or May." Cut a penstemon down in autumn and you have removed the thing that was keeping it alive.
Seedheads that earn their keep through the winter: hydrangeas, eryngium, phlomis, hardy geraniums, miscanthus. Leave those and cut them in spring.
The lawn
Grass does not simply stop. The RHS reckons on growth continuing "in temperatures above 7°C", which in a mild autumn here means the mower is not finished in October. Their November advice is to mow "if necessary during mild weather" and to raise the cutting height about 5mm above where you had it in summer.
You'll see a specific soil temperature quoted all over the internet as the moment growth stops. I've looked for a source I'd stand behind and couldn't find one, so I'm not repeating it. Watch the grass instead of the calendar — if it's growing, it wants cutting, just higher and less often.
The one hard rule: don't mow or walk on frosted grass. The RHS says it flatly, and you can see why — the blades are frozen stiff and they break rather than bend. Footprints across a frosted lawn show up as brown tracks for weeks. If it's white, stay off it.
And the wider point
Frosts are getting less frequent. The Met Office's own 2025 stocktake records that air and ground frosts "have steadily declined from the 1980s, with now more than two weeks' fewer air frosts in the most recent decade (2015-2024) compared to the period between 1931-1990".
That is not a reason to stop protecting things. It's a reason to stop trusting the date you have in your head from twenty years ago. The frosts are fewer, they still come, and the one that catches people is the early one in a mild autumn when nothing has been put away.
If you'd rather someone else did the deciding and the lifting, that's a normal autumn visit — get in touch and I'll come and look at what you've got.