What's Wrong with My Poinsettia?

Poinsettia is native to warm Mexican hillsides and reacts to cold with immediate leaf drop. The trip home from the store in an unheated car, a cold draft from a door or window, or a spot near an air vent can all trigger mass shedding within a day or two. The leaves go limp and fall while still green.

Poinsettia roots sit in a dense, fibrous root ball that holds moisture and rots quickly when the pot stays wet. Soggy soil cuts off oxygen to the roots, and the plant drops leaves as it shuts down. Yellowing often accompanies the drop.

Poinsettia's dense, compact root ball suffocates fast in waterlogged soil. As roots die, the plant pulls nutrients from its oldest leaves first, turning them yellow from the bottom of the stem upward.

Temperatures below 55°F damage poinsettia's tropical leaf tissue. Cold-damaged leaves yellow in patches and drop, often the day after a cold night near a drafty window. The damage is not reversible in the affected leaves, but the plant recovers once it warms up.

As the colorful bracts age and fade in late winter, poinsettia naturally sheds older leaves while it rests. If the bracts have already dropped and only the older lower leaves are yellowing while the stem tips look firm and alive, this is the plant winding down for the season, not dying.

Poinsettia's broad leaves wilt fast when the soil goes dry. Unlike succulents, this plant has no water reserves in its stems or leaves and droops quickly once the root ball dries out. The soil will feel light and bone dry.

Rotten roots cannot absorb water, so the plant wilts even in wet soil. The wet-soil-plus-wilt combination is the key sign this is rot rather than thirst. Poinsettia's fibrous root ball breaks down fast in soggy conditions.

Poinsettia is a short-day plant. It needs 14 or more hours of complete, uninterrupted darkness every night for about eight weeks in fall to produce the colored bracts. Even a few minutes of light during those dark hours resets the process. A plant left in a normally lit living room will stay green all the way to December.

Poinsettia is the classic whitefly host plant. Tiny white insects live on the underside of leaves and launch into a cloud when you brush the plant. They suck sap and leave sticky honeydew on the broad leaves, which then grow a black sooty mold. A heavy infestation can cause leaf drop.

Dry indoor air in winter, exactly when poinsettia is on display, creates perfect conditions for spider mites. Fine webbing appears on the undersides of leaves and between stems, and the broad leaf surface shows pale, stippled speckling as the mites drain the cells.