Why Winter Hits Indoor Plants So Hard

Most of the plants we grow indoors are tropical by nature. Monsteras, philodendrons, peace lilies, rubber plants and calatheas all evolved under a canopy where light is bright, humidity is high and the temperature barely shifts. A British living room in January offers the opposite: perhaps seven or eight hours of weak daylight, central heating running for hours, and a draught every time a door opens.

The plant's response is sensible rather than dramatic. With less light, it cannot photosynthesise at summer speed, so growth slows and it needs far less water. If you carry on watering as you did in July, the compost stays wet, roots suffocate and rot sets in. Meanwhile the dry air pulls moisture from leaves faster than the roots can replace it, which is why you often see brown crispy edges and yellowing lower leaves at the same time as soggy soil.

The good news is that a few adjustments in late autumn will carry most plants through to March in decent shape. The trick is to think about light, water, humidity and warmth together, because changing one affects the others.

Cut Back on Watering, But Do It Properly

Overwatering is the single biggest killer of houseplants between November and February. Rather than following a weekly schedule, test the compost before you reach for the watering can.

• Push a finger in up to the second knuckle. If it feels cool and damp, wait. For larger pots, a bamboo cane or a cheap moisture meter works well.
• Water thoroughly but less often. When the top few centimetres are dry, water until it runs out of the drainage holes, then empty the saucer after twenty minutes. Never let pots sit in a puddle.
• Use tepid water. Cold tap water shocks tropical roots. Let a jug stand overnight so it reaches room temperature and some chlorine dissipates.
• Expect big differences between plants. A cactus or snake plant may need water once a month; a fern in a warm bathroom might still want a drink every week.
• Ease off entirely for dormant plants. If nothing is growing, a light watering every three to four weeks is often plenty.

Plants in small pots dry out faster than those in generous containers, so check them more often. Terracotta dries quicker than glazed ceramic or plastic, and a radiator nearby will speed things up further.

Raise Humidity Without Drenching the Carpet

Central heating can drop indoor humidity to 30 per cent or lower, which is desert-like for a plant that expects 60 to 70 per cent. Misting helps for a few minutes at best, and on plants with fuzzy leaves such as African violets it can encourage rot. Better options:

• Group plants together. Transpiration from one leaf creates a slightly damper microclimate around its neighbours.
• Use a pebble tray. Stand the pot on a layer of gravel in a saucer of water, keeping the base of the pot clear of the water line.
• Move humidity lovers to the bathroom or kitchen. A bright bathroom with a window is ideal for ferns, calatheas and orchids.
• Invest in a small humidifier. Run it for an hour or two in the evening near your thirstiest plants.
• Double-pot. Sink a smaller pot into a larger one filled with damp sphagnum moss, which releases moisture slowly.

Keep an eye out for condensation on windows and mould on walls, and dial the humidity back if either appears.

Chase the Brightest Light You Can Find

Light is the limiting factor in winter, so treat it as a resource to be shared out carefully. Move plants closer to south- or west-facing windows between October and February, and remember that a metre of distance from glass can halve the light a plant receives. Clean windows inside and out, and wipe dusty leaves with a damp cloth or give them a lukewarm shower, since a film of grime blocks precious daylight.

Rotate pots a quarter turn every week or two so growth stays even rather than leaning towards the glass. If your windows are small or shaded, a simple LED grow light on a timer for six to eight hours a day makes a remarkable difference to ferns, succulents and herbs. Plants that go fully dormant, such as some aloes and begonias, can simply be rested in a cooler, dimmer corner until spring.

Mind the Temperature and Draughts

Most tropical houseplants are happiest between 18°C and 24°C during the day, dropping a few degrees at night. Blasts of hot air from radiators and wood burners desiccate leaves, while cold glass and draughty hallways can chill roots and cause blackened, mushy damage.

• Move pots off windowsills after dark in very cold spells, or slip a piece of card between the pot and the glass.
• Avoid positioning plants directly above radiators or in the path of an air-conditioning unit.
• Shield plants from open doors and letterboxes. Even a short blast of freezing air can mark tender foliage.

If a room is unavoidably warm and dry, that humidity tray becomes even more important.

Pause the Feed and Watch for Pests

Feeding a plant that is not growing simply salts up the compost. Stop feeding from roughly November to February, or dilute to half strength for plants still pushing out new leaves under grow lights. Hold off repotting too, unless a pot is waterlogged or a plant has outgrown its home badly. Pests such as spider mites, fungus gnats and mealybugs thrive in dry, warm indoor air, so check the undersides of leaves and the joints where stems meet when you water. A weekly wipe or a shower with the spray attachment keeps most problems at bay.

Above all, be patient. A dropped leaf or two in January is normal, not a crisis. Resist the urge to compensate with extra water, keep the compost on the dry side, and your plants will reward you with a burst of fresh growth once the light returns in March.