Check for: Yellowing leaves. It may be counterintuitive, but yellow foliage is often a sign of too much water. Since some houseplants are semidormant over the winter months, they don’t need nearly as much water as they do in the summer.
What to do: Clip off the affected leaves, and hold back on watering until the soil feels dry. If the plant stays green, the problem is solved. If yellowing persists, it could mean an iron deficiency. Try amending the soil with an iron supplement.
Check for: Dead or shabby foliage. This not only looks unappealing but can also lead to fungal or other diseases if left to rot in the pot.
What to do: Unlike in outdoor gardening, you shouldn’t leave rotting leaves untouched. Pinch them off and toss them out.
Check for: Dust on leaves. Clogged stomata (that’s what the pores are called) prevent plants from transpiring.
What to do: Wipe the tops and undersides of smooth foliage with a soft dustcloth.
Check for: Water seeping through terra-cotta or other porous saucers. Excess moisture can harm floors and furniture.
What to do: Use waterproof glazed saucers, or place cork coasters beneath unglazed terra-cotta ones to prevent water damage.
Check for: Dry, brittle leaves. If your skin is extra-dry because of indoor heating, chances are your plants are feeling it, too.
What to do: Add moisture to the air around your plants by setting pots on pebble-filled trays of water, or use a humidifier.
Check for: Pests. White fuzz suggests mealybugs, tiny “brown helmets” on stems indicate scale (a sap-sucking insect), and webs and red dots are signs of spider mites.
What to do: Dab away mealybugs with a rubbing alcohol–soaked cotton swab, cut off stems infested with scale, and give plants with spider mites a cold shower.
Check for: Shoots of excess growth. Houseplants are better off conserving their resources in winter. Too much growth now can weaken a plant over the long term.
What to do: Prune new top growth to strike a balance between the roots -- which grow more slowly in winter -- and the shoots.