Bringing potted plants indoors: when and how

Once night temperatures drop below 10 degrees Celsius, your potted plants need to come indoors, and not all at the same time. Tender tropical species such as hibiscus and citrus should move inside by mid-October, while hardier plants such as hydrangea and lavender can often stay outside until early November.

The most common mistake is bringing everything in together and parking it right next to the radiator. That causes stress, pests and leaf drop. Below you will find, species by species, when to bring plants in, how to check for pests first, and how to keep them healthy until spring returns.

The temperature threshold per species: when does it get dangerous?

Not every potted plant is equally sensitive to cold. The exact threshold depends on wind, humidity and whether the plant stands exposed overnight, but these rules of thumb work well in practice.

Tropical potted plants: hibiscus (Hibiscus rosa-sinensis), bougainvillea (Bougainvillea spp.), fuchsia, pelargonium, mandarin orange (Citrus reticulata), lemon tree (Citrus limon) and oleander (Nerium oleander). These love warmth and start struggling as soon as night temperatures approach 10 degrees. At 5 degrees you see leaf drop, below 0 they freeze. Bring them in from late September to mid-October: in Flanders usually around mid-October, in the northern Netherlands a little earlier because the first night frost arrives sooner there.

Moderately frost-tolerant potted plants: cherry laurel (Prunus laurocerasus), rhododendron (Rhododendron spp.) in a pot, Ilex crenata (the well-known boxwood substitute), ivy (Hedera helix) in a pot and some ferns. These handle temperatures down to 5 to 8 degrees without damage and can stay outside until late October, sometimes into early November if it does not turn cold quickly.

Frost-resistant potted plants: hydrangea (Hydrangea macrophylla), lavender (Lavandula angustifolia), rosemary (Salvia rosmarinus), blue cypress and some boxwood varieties (Buxus sempervirens) in pots. These survive light frost down to roughly minus 5 to minus 8 degrees, but note: roots in a pot freeze faster than roots in open ground, because the pot offers far less insulation. Move them to a sheltered spot by November at the latest, even though they could technically handle a bit longer outside.

What matters more than air temperature is the soil temperature inside the pot. A pot in full sun feels warm at midday but cools quickly and deeply overnight, especially in wind.

Check for pests before bringing plants indoors

Potted plants that spent the summer outside often carry unnoticed scale insects, mealybugs or spider mites. Bring the plant inside like that and the population explodes in the warm indoor air, leaving you with an infestation in your living room from November to April.

Scale insects: tiny brown or grey-green shells on stems and the underside of leaves, common on citrus, olive and ficus. Wipe them off with a damp cloth or a cotton swab dipped in rubbing alcohol, and repeat after a week.

Mealybugs: white, cottony clusters in leaf joints, often on succulents, orchids and ficus. Remove them with a cotton swab and rubbing alcohol, then keep the plant separate from your other plants for two weeks.

Spider mites: fine webbing on the underside of leaves and yellowing foliage, especially after dry heat. Rinse the plant well with a garden hose outside before bringing it in, which removes both mites and dust.

Thrips: silvery flecks on leaves and tiny black dots on flowers. A light infestation often responds to a yellow sticky trap; for a heavy infestation, insecticidal soap is an option that is safe for home use.

Is the plant heavily infested? Let it acclimatise for two to three weeks before you start treatment, otherwise the combined stress is too much for the plant.

Timing: when exactly is the right moment?

Timing depends on two things: your region and the species.

Tropical plants such as hibiscus, citrus and fuchsia: late September to mid-October. Do not wait until it is already cold, or you will already see leaf drop and stunted growth. If evenings are still around 15 degrees and just feel a bit fresh, bring them in anyway: that way they adjust gradually to indoor air instead of facing a sudden shock.

Moderately frost-tolerant plants such as cherry laurel and rhododendron: mid-October to late October.

Frost-resistant plants such as hydrangea, lavender and rosemary: these can stay out longest, until early November, as long as no hard frost is forecast.

In practice, just watch the weather forecast. If three nights in a row are forecast below 10 degrees, that is your signal. Better a week too early than hauling pots indoors in the dark because of unexpected frost.

Preparation: inspection and cleaning

Give each plant a short inspection before it comes in.

Foliage: yellow spots, insects, or a grey haze on the leaves (that is botrytis mould)? Gently wipe affected leaves and then place the plant in drier air.

Stems: broken or damaged stems are best cut off, since they heal poorly indoors and invite disease.

Pot and root ball: roots growing out of the drainage holes, or soil as hard as concrete? Avoid repotting right before the move, that is too much trauma at once. Do check moisture: feels dry? Give it a thorough watering outside, let it drain fully, then bring it in.

Pot rim: a green algae film on the rim or a compacted top layer can be gently loosened and topped up with fresh potting soil, which reduces disease pressure indoors.

Also wipe the leaves with a damp cloth. Removing dust and pollen lets more light through, and a clean plant simply grows better.

The spot indoors: light, temperature and humidity

Light: potted plants need light above all, not just warmth.

• Place them by a window, ideally facing south or west.
• Citrus, oleander and hibiscus prefer 4 to 5 hours of direct sun a day.
• Fuchsia, begonia and pelargonium can take a bit less light, but not a dark corner.
• Cherry laurel and ficus are less fussy and can sit further from the window.

Do not tuck a plant three metres from the window in a corner, it will survive there, but it will not thrive.

Temperature: most tropical potted plants dislike sitting right next to central heating. Ideal is cool and bright: no warmer than 12 to 15 degrees at night, 16 to 18 during the day. That feels cooler, but your plant grows more slowly, uses less water, does not become etiolated (long and thin), and pests multiply more slowly too. Finding that uncomfortable for yourself? Place the plants on a cool windowsill or in an unheated hallway instead, a hibiscus by a hallway window does perfectly well there.

Humidity: central heating dries out the air sharply, which attracts spider mites. Group your potted plants close together so they humidify each other, place a saucer of water under the pot (never stand the pot itself in water), and mist the leaves every two weeks with a plant sprayer. Air the room for fifteen minutes now and then too, which helps prevent mould.

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Watering in winter: less, but never none

Many people think you should stop watering entirely in winter, since the plant is not growing anyway. That is not quite right: the plant does grow much more slowly and uses less water, but a root ball that stays constantly wet rots just as easily in a cool, dark hallway.

Moisture test: push a finger two centimetres into the soil. Feels moist? Skip the water. Feels dry? Water it. Check this once a week.

Water temperature: use room-temperature water, never ice-cold water straight from the garden hose, which causes root shock.

Frequency: if you watered twice a week in May, expect roughly once every two weeks in December, depending on species, pot size and location.

Consistency: feeling the soil every week beats panic-watering heavily now and then.

Preventing mould and root rot in the winter shelter

Mould thrives in a cool, damp hallway, and root rot develops in soil that stays wet too long.

Prevention: air the room for twenty minutes once a week so damp air can escape. Remove fallen leaves straight away, they rot and feed mould. Water from below through a saucer rather than from above, since wet leaves invite mould.

Recognising it: a grey haze on leaves or stems is usually botrytis. Gently wipe the affected part, place the plant somewhere drier and reduce watering.

Is the base of the stem already soft and rotten? Then the plant is usually beyond saving. Refresh the potting soil, cut back to healthy wood and hope for regrowth, the chance is small but not zero.

Step by step

Step 1: Check for pests

Inspect leaves, stems and leaf joints for scale, mealybugs and spider mites. Rinse the plant outside or treat it with a cotton swab and alcohol.

Step 2: Run the moisture test

Push a finger into the soil. Dry? Water it and let it drain fully. Moist? The plant is ready to move inside.

Step 3: Clean the foliage

Wipe the leaves with a damp, soft cloth so dust and pollen are gone and the plant sits in clean light.

Step 4: Choose the right spot

Place tropical plants by a south or west facing window, other potted plants can sit a little further from the light.

Step 5: Adjust your watering

Check the root ball weekly and only water once it feels dry, usually every 10 to 14 days in winter.

Step 6: Keep humidity up

Group your plants together, place a water saucer under the pot, mist every two weeks and air the room weekly.

Frequently asked questions

Should I prune my plants before bringing them indoors?

No, pruning creates wounds that heal poorly in winter. Wait until April. Do remove dead leaves and dead twigs, since those will not come back anyway.

Can my lemon tree sit in a dark hallway?

No. Citrus needs light, ideally at least three to four hours of sun a day, even in winter. Kept too dark, it drops its leaves and will not flower.

What is the minimum winter temperature for my hibiscus?

At least 12 to 15 degrees, ideally kept constant. Below 10 degrees at night it loses leaves, below 5 degrees it dies.

My citrus keeps drying out in winter, what am I doing wrong?

Soil in a pot dries out faster than soil in open ground, especially close to a window. Water a little more often, not three times as much, and check the root ball weekly.

See it in your own garden first

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