Houseplants in winter

Move your plants closer to the window. A spot that worked at six feet from the glass in July delivers too little in December. Even a south window in winter gives less than a north window in June.

Clean the glass and pull heavy curtains right back. Both sound minor and both make a visible difference on a gray day.

Wipe the dust off the leaves as well. A closed layer of dust costs light the plant cannot spare now. A damp cloth is enough, and a soft brush for hairy leaves.

Turn the pots a quarter turn every few weeks so the growth does not lean into the window on one side.

A grow light is the only real substitute for light that is not there. It has to hang close enough above the plant and run for several hours a day, otherwise it stays decoration.

A shoot that comes out long, thin and pale in winter is not growth worth keeping. Cut it back in spring and the plant will put out compact new growth in better light.

Most houseplants need water less often in winter, but not all of them, and not on a schedule. Before you water, or decide to hold off, run through four checks.

The gap between waterings gets longer while the amount stays the same. When you do water, water thoroughly until it runs out of the bottom.

A spot directly above a radiator turns that around. There the root ball dries out faster than in summer even though the plant is barely growing, so those pots need water more often rather than less.

Use water at room temperature. Cold water straight from the tap lands on roots that are used to a heated room.

Soil that stays wet at a low temperature is the most common way to lose a plant in winter. The roots work slowly, the water sits there, and root rot follows. Overwatering also makes leaves droop, so a limp plant in wet soil needs drying out, not more water.

• Moisture. Feel two inches down. Still damp: wait. Dry: water thoroughly.
• Drainage. Lift the pot out of its saucer or cover. Water standing at the bottom keeps the roots wet, so tip it away about ten minutes after watering.
• Light. A plant in a dim spot uses little water and its soil stays wet for longer. Move it closer to the window before you change how much you water.
• Active growth. New leaves, buds or a flower spike mean the plant is working and needs water whenever its soil dries. A plant at rest needs less.

Window light. Put the plant as close to the brightest window as its leaves allow. Light drops quickly with distance from the glass, so a plant a few steps into the room gets far less than one by the window.

Radiator. Keep plants off the sill directly above a radiator and out of the warm air rising from it. That air scorches delicate leaves and dries the soil fast. A table or shelf beside the window, out of the updraft, is the better spot.

Cold glass. On frosty nights leaves touching the pane get chilled, and a plant shut in between a closed curtain and the window sits in trapped cold air. Keep a gap between leaves and glass, leave the plant on the room side of the curtain, and set a wooden board or a piece of foam board under pots on a cold sill.

Heated air is dry, and thin-leaved plants such as ferns, calatheas and indoor palms show it first. Group them together, or stand the pot on a tray of pebbles and water so it sits above the water rather than in it. Misting lasts minutes and replaces neither.

Brown tips do not prove dry air on their own. A radiator, a cold draft, soil that dried out completely, roots standing in water and salts from fertilizer all brown leaf tips too. Check the soil and the spot before you change anything.

If you are unsure whether a spot is bright enough, measure it. The Light Meter in the Botanicaly app, part of Botanicaly Pro, reads the light where the leaves sit, with the phone’s light sensor on Android or a camera estimate on iPhone. It compares the reading with the range the saved plant needs. Measure in daylight, and again at another time of day.

Move the plant aside before you open a window. Cold air straight onto warm leaves drops the foliage of a weeping fig and other sensitive species within days.

Do not fertilize in winter. A plant that is barely growing in low light does not take the nutrients up, and the salts stay behind in the root ball.

The exception is a plant that is growing or flowering now, such as cyclamen and amaryllis. Those get a weak feed while they are in growth, as their own guides describe. A Christmas cactus gets no feed in winter. Its feeding stops in late summer.

Repot in winter only when a problem forces it, such as soil that will not dry, soft brown roots or a broken pot. With no reason to hurry, wait for spring.

Hold off on larger cutbacks too. The plant is hardly putting out new growth now, so cuts take a long time to heal. Single damaged leaves can come off at any time.

Spider mites are the typical winter pest. Warm dry air is their best condition, and they build up quickly in heated rooms.

Look at the leaf undersides regularly, above all on plants sitting over a radiator. Fine pale speckling on the upper surface and thin webbing in the leaf joints are the first signs.

Mealybugs also turn up more often in winter. They sit as white cottony dots in leaf joints and along stems and stay hidden for a long time in dense growth.

Look new plants and holiday gifts over carefully before they join the others. Two weeks on their own spot is enough to notice an infestation.

Not every houseplant wants a warm living room in winter. Cacti, many succulents, citrus, oleander and olive want a bright cool place where they are watered very little.

For many of those species that cool rest is what makes flowers possible the following year. A spot that stays warm all winter costs them the bloom.

Plants that grow or flower in winter are the exception to watering less. They keep using water while they are active, so their soil decides, not the season. Each one has its own rule:

Bring plants that spent the summer outdoors back in before the nights turn cold. Check them over for pests first and rinse the leaves off.

• Christmas cactus: Usually in bud or in flower in winter. Keep the soil evenly moist then, because dry soil makes the buds drop, and do not move or turn it. Pet-safe (non-toxic).
• Cyclamen: Grows and flowers from autumn into spring. Water from below when the top of the soil feels dry and keep it cool and bright. Its rest comes in summer, after flowering. Toxic to cats and dogs.
• Indoor azalea: Flowers in winter and must not dry out. Check the compost daily, water when the surface is slightly dry and use rainwater if your tap water is hard. Toxic to cats and dogs.
• Moth orchid: A plant pushing a flower spike is growing. Water when the bark is nearly dry and the roots look silvery, and keep water out of the crown. Pet-safe (non-toxic).
• Amaryllis: Keep the soil barely moist until the shoot shows, then water whenever the surface begins to dry while it grows and flowers. Toxic to cats and dogs.