Poinsettia dropping leaves

Cold is the most common cause. A poinsettia can suffer chilling damage below about 10 °C (50 °F) and drop leaves. Frost or a long spell of cold can kill it, and even a few minutes of frost on the way home can blacken the leaves.

Keep it at 15 to 21 °C (59⁠–⁠70 °F), with the leaves off cold glass and away from doors that open onto winter air. When you buy one in cold weather, have it wrapped for the trip home.

Poinsettias are often sold in a foil sleeve with no hole. Water that collects there keeps the soil soaked and the roots wet, and wet soil from water standing in the sleeve makes leaves drop.

Take the plant out of the sleeve to water it, let it drain and empty the saucer. Water again only when the top 2.5 to 5 cm (1⁠–⁠2 in) of soil is dry.

When a poinsettia dries out, its leaves curl and fall. Feel the soil with a finger. If the top is dry, water until it runs out of the bottom, then empty the saucer.

Leaves and bracts that wilt and turn black point to cold instead. That damage cannot be undone.

Warm, dry air makes the leaves drop. Keep a poinsettia away from radiators and heating vents.

Ordinary room humidity is enough. Do not mist it, because wet bracts can get gray mold.

If a poinsettia loses most of its leaves after Christmas, let it rest somewhere cool, about 10 to 13 °C (50⁠–⁠55 °F), and water only enough to stop the stems shriveling.

In March or April, cut the stems back to 10 to 15 cm (wear gloves, the milky sap can irritate skin), repot one size up if roots fill the pot, and start feeding.

Think about what changed in the last few days: a cold trip home, a new spot by a window or door, a heater nearby, or a different watering routine. Fix that first.

Then keep the plant bright, at 15 to 21 °C (59⁠–⁠70 °F), and water only when the top 2.5 to 5 cm (1⁠–⁠2 in) of soil is dry.