Quick answer

Bring pelargoniums under cover once forecast nights approach 5C, which is usually early October in the north and late October to early November in the south, and always before the first frost warning. Cut them back by a third to a half, check the compost for vine weevil, then keep them cool, light and nearly dry until March.

Most people searching how to overwinter geraniums UK in October want two things: is it time yet, and which method is worth the bother. The calendar gives a rough window; the forecast and the plant in front of you settle it, so this article is built around those signals rather than a date.

A note on naming. The fleshy-stemmed pot and bedding geraniums are pelargoniums: zonal, ivy-leaved, regal and scented-leaf types. Hardy cranesbill geraniums, the wiry border plants, need none of this.

Table of contents

Read the plant and the forecast before the calendar

Three checks take about ninety seconds per plant and tell you more than any date.

The forecast

Pelargoniums stop growing below about 7C and suffer with repeated nights under 5C, well before an actual frost, so the number to watch is the forecast overnight low. Two or more nights at 5C or under in the five-day outlook is the move-in signal; a frost warning means move tonight, not this weekend.

Where you are shifts this by weeks. Inland Scotland and the uplands commonly see a first frost in early to mid October; the Midlands and the south typically wait until late October or November; coastal Cornwall or a city centre may not frost until December. A sheltered south-facing wall buys a week or two; a frost pocket loses it.

The plant

Look at the stems first. Firm green or woody stems with no soft patches near the base mean a plant worth keeping. A stem that gives under thumb pressure, or has a dark water-soaked patch at soil level, is already rotting and will not improve indoors: take cuttings from the healthy tips and compost the rest.

Yellowing lower leaves in October are normal. Yellow leaves with grey fuzz underneath, or a mat of dead leaves on the compost, mean botrytis is established and the plant needs a hard tidy before it goes near a closed space.

Then knock the plant out of its pot. Healthy roots are white or cream and fill the compost. Creamy C-shaped grubs with brown heads, up to about 1cm long, are vine weevil larvae, and a rootball that falls apart in your hand is a cuttings-only case.

Types behave differently

Zonals, the classic bedding type with a dark band on the leaf, are the toughest and take a hard cut without complaint. Ivy-leaved trailers have brittle stems and dense growth, the most prone to botrytis in a stuffy room, so thin them harder than you think. Regals flower on last year's growth, so a hard autumn cut costs you the spring show: trim lightly and keep them growing. Scented-leaf types tolerate a windowsill best.

Plants bedded out in the ground need lifting into pots a week or two before the move-in signal, with as much root as you can keep, then a sheltered spot outdoors to recover.

What to do from September to March

These are typical timings for a mid-latitude English garden. Shift everything two to three weeks earlier for northern Scotland and upland sites, and the same amount later for the far south-west and sheltered city gardens. A mild year and a cold one can differ by a fortnight in the same garden, which is why the forecast overrides the month.

September

Nothing needs moving yet in most of the country, but this is the month for cuttings: plants are still in active growth and cuttings root in two to four weeks, well before the light collapses. It is also the month to find out whether your chosen space holds above 5C overnight.

October

The main month. In the north, plants usually come in during the first half; in the south, the second half or into November. Move each plant when its signal arrives rather than doing the lot on one weekend.

November

Everything tender should be under cover by mid-month even in mild areas, because the first hard frost in the south often lands in late November. Inside, the job switches to restraint: water only when the compost is dry right through, pick off yellow leaves, and open a door on dry days.

December and January

The plants are doing nothing and you should do almost as little. Check once a fortnight for mould and soft stems, and water a cut-back plant perhaps once a month. This is when single-glazed greenhouses and unheated porches fail, so watch the lows on clear nights and be ready to move pots indoors or throw fleece over them.

February

New shoots at the base of a cut-back plant are the sign to water a little more often. Bare-root plants get potted up in the second half of the month so they have time to show whether they are alive.

March

Repot into fresh compost, trim leggy winter growth back to a healthy pair of leaves, and feed at half strength once new growth is obvious. Plants stay under cover until the frosts are over, usually May.

The four methods, step by step

All four start the same way: cut back, clean up, check the roots. Then your space decides the method. A windowsill only: keep one or two plants growing and take cuttings from the rest. A frost-free greenhouse or porch: cut back and keep them semi-dormant, which is what we would do with most zonals and ivy-leaved plants. Bare-root storage is for a cold garage, a lot of plants, and the stomach to lose a third of them.

The preparation every method needs

Cut each plant back by a third to a half with clean, sharp secateurs, each cut just above a leaf joint, and take out any stem that is soft, dark or crossing through the middle. Strip every yellow leaf, flower and bud. Knock the plant out of its pot, check for vine weevil grubs, and either repot into fresh compost or scrape off the top centimetre of the old, where moss and fungus gnat eggs live.

Method 1: keep it growing in a light, frost-free place

This suits scented-leaf and regal types. It needs the brightest spot you have: a south or west windowsill in a cool room, a conservatory, or a greenhouse held above 5C. Water when the top few centimetres are dry, roughly every ten days to a fortnight, and do not feed until March.

Before trusting a porch or greenhouse, find out what it does at 3am in January rather than what you assume. A max-min thermometer left in place through a week of cold nights answers that; the max-min greenhouse thermometer review covers what the cheap ones get right and wrong. If the minimum reads 2C, add a heater or bubble wrap, or bring the plants into the house.

Method 2: cut back hard and keep semi-dormant

Our preferred method for zonals and ivy-leaved plants. Reduce each plant to a framework of stems 10 to 15cm high with a few leaves left on, and stand the pots close together somewhere cool and light at 5 to 10C: a frost-free greenhouse, a porch or an unheated bedroom windowsill.

Water so little it feels wrong: every two to four weeks, and only once the pot feels light and the compost has pulled away from the sides. Give enough to moisten, not soak. If the remaining leaves wrinkle, the plant needs a drink; if they yellow and drop, it is too wet or too dark.

Method 3: bare-root storage

The old method, and the one with the worst survival rate: some growers get most plants through every year, plenty lose half. Shake off all the compost, trim the roots to about 10cm and the top to about 15cm, and let the plant dry on newspaper for a day. Then hang it upside down, or lay it in a cardboard box of dry compost, in a dark place that stays between 5 and 10C, typically a garage or insulated shed.

Check monthly. Stems should be firm and slightly leathery; one that has shrivelled to a stick or gone soft and grey comes out before it infects the rest. Growers disagree about whether to soak the roots for an hour once a month or leave them alone: if stems are shrivelling by December, soak; if they look fine, leave them. Pot up in late February.

Method 4: cuttings as insurance

Take these in September while growth is strong, or from the material you cut off in October. Choose non-flowering shoots 7 to 10cm long, cut just below a leaf joint, strip the lower leaves and leave the top two or three. No rooting hormone is needed. Push the cuttings around the edge of a pot of gritty compost, water once, and stand them somewhere light but out of direct sun. Do not cover them with a bag; that invites botrytis, which kills more cuttings than drought does.

Rooting takes two to four weeks at 15 to 20C, longer in a cool room. Gentle bottom heat makes a real difference to late cuttings, and a heated propagator with the lid off is the simplest way to provide it; the heated propagator review explains why the middle of the tray runs warmer than the edges. Pot on singly once roots show at the drainage holes.

Spot problems early and recover

Stem rot from overwatering. The base goes dark and soft and the plant collapses while the leaves still look fine. Cut above the rot; if the tissue is clean and green, take cuttings from the tips and discard the rest. Water less.

Grey mould. Botrytis shows as fuzzy grey growth on dead leaves, then spreads to live stems as brown lesions. It thrives in still, damp air, so a closed porch full of leafy plants is exactly what it wants. Bin affected leaves, space the plants out, and ventilate on dry days.

Pale, stretched growth. Long thin yellow-green shoots with leaves far apart mean too much warmth for the light available, the classic centrally heated windowsill problem. Move the plant somewhere cooler, or cut the leggy growth off in March. Do not feed a stretching plant.

Vine weevil. A plant that wilts in moist compost or lifts clean out of its pot has grubs eating the roots. Wash the roots, pick out every grub, and repot into fresh compost. Nematodes only work while the compost is above about 5C, so a September or early October treatment before the plants come in is the window; the vine weevil nematode review explains the two-week shelf life and why timing decides whether they do anything at all.

Plants that dry out in bare-root storage. Stems gone papery and light are usually dead. Soak the roots for an hour, pot up in barely moist compost, and give them a warm light spot for three weeks; if nothing shows, compost them.

Frost through single glazing. Leaves go dark, limp and translucent overnight and stems blacken from the tips. Cut back to firm tissue and keep the plant dry and cool; zonals often regrow from the base if the rootball did not freeze. Then fix the space with a frost-guard heater, bubble wrap or fleece on the coldest nights; the frost protection guide covers the options.

Frequently asked questions

Can geraniums survive winter outside in the UK?

Pelargoniums cannot survive a proper frost outdoors anywhere in the UK, though in mild coastal towns and sheltered city courtyards some scrape through a soft winter. Hardy cranesbill geraniums are a different plant and stay in the ground. A cranesbill has thin wiry stems; a pelargonium has thick, fleshy ones.

Should you cut geraniums back before bringing them in?

Yes, for every method except a windowsill plant you want to keep flowering. Cutting back by a third to a half reduces the leaf area that needs light and water and removes the growth most likely to catch botrytis. Regals are the exception: trim lightly.

How often should you water geraniums over winter?

As little as you can get away with. A cut-back plant in a cool room typically wants a small drink every two to four weeks, and only when the compost is dry right through. Overwatering kills far more overwintered pelargoniums than cold does.

Is it better to take cuttings than keep the old plant?

For zonal and ivy-leaved types older than two or three years, yes. Young rooted cuttings take a fraction of the space, carry fewer pests, and make bushier plants by June than a woody parent will. Keep the parent too if you have room, but not as the only copy.