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Poinsettia (Christmas Star) plants are the famous holiday plant. Sales spike around Thanksgiving. The plant has its own dedicated Poinsettia Day on the 12th December, by which time, it’s been in the home long enough to start showing signs of stress.
Although these are now grown commercially in the US, they are native to Mexico, a country known for its warmer climates and humid air.
Replicating those conditions indoors is not always plain-sailing. That’s why Poinsettias are mainly annuals – used once, tossed, replaced the following year.
Poinsettia leaf curl is one of the earlier signs of stress, even in the first year when new. The most common causes of curling, wilting and drooping leaves relates to inadequate watering, drainage, light conditions, room humidity, and too much fertilizer.
6 Causes of leaf Curl on Poinsettia Plants Explained
1 – Overwatering – This Causes Downward Leaf Curl
Downward leaf curl, sometimes referred to as leaf tip cupping or curling on the poinsettia plant is indicative of too much water.
Overwatering leads to damp soil, oxygen availability decreases, therefore, the roots can’t absorb what water is there. The plants defense is to curl at leaf tips and leaf margins to try to retain the moisture it does have.
The fix for an overwatered poinsettia depends on the extent of damage to the root zone.
For slightly damp soil, referring to soil that’s damp to a depth slightly deeper than a couple of inches, it should be possible to leave it a couple of days without water. Watch how the leaves change shape.
As the soil dries, moisture uptake will begin again. The plant will settle down, dropping the defensive behavior or curling the leaf tips to conserve moisture.
When the soil has been waterlogged for a while, root rot can take hold. If that happens, wilting, curling and drooping is only the start of much worse problems to come later. Rotted roots need to be removed before it kills the plant.
For completely waterlogged soil, the best course of action is to repot the plant completely. That includes replacing the soil because waterlogged mediums are a festering ground for bacteria and fungi spores to germinate.
These weaken plants, and that makes them susceptible to numerous plant diseases, and attractive to mealybugs, aphids and several other common houseplant pests.
Pests are like bullies, always going for the weakest plants in your collection. To prevent a rapid deterioration of any potted plant in waterlogged soil, repot it in a fresh growing medium, and rinse the pot out before adding the soil.
2 – Leaving the Decorative Foil on Renders Drainage Holes Redundant
In garden gift stores, poinsettia sales season is between Thanksgiving and Christmas. Stores decorate the pots with decorative foil wrapping that does two things.
First, it is a decorative packaging, designed to inspire you to buy the thing. It’s marketing. Secondly, it lowers the number of times staff need to water the plant. That’s maintenance reduction. Without holes in the foil, the water they do add is retained in the soil.
When customers take it home, or receive the plant in all of its decorative abundance, the foil should either be removed entirely, or enough holes should be poked in the foil to allow water to drain freely before adding more water.
Without doing this, it causes drainage issues, and that is the second most common reason for a poinsettia dying, second only to overwatering, because the effects are the same. Direct root zone damage.
3 – Cold Temperatures
The poinsettia plant favors warm climates. It cannot cope with any cold temperatures, even if that is only a draft from an old window frame, or a slight breeze from an open window.
Leaf curl can be a symptom of early cold shock. If the soil is adequately watered, consider the placement of the plant pot.
Is it near to a window where a cold draft could be hitting the leaves? Is there an air vent near it, or an air conditioning unit pushing cool air directly at the plant?
Any cool air drafting onto leaves can result in curling. Given these need a lot of natural light for the red bracts to stay vibrant, the windowsill is the usual space these are placed.
Feel around the window frame and the sealers to make sure there aren’t gusts of cold air getting through when the wind picks up.
Similarly, if you place it near to a frequently used door, the regular drafts from the door opening can harm it. That’s how sensitive the leaves are.
4 – Lack of Humidity
The Christmas Star is almost always used as a potted indoor plant. Humidity is a factor that needs to be addressed because the ideal humidity for you is too low for the plant.
A healthy humidity range indoors is between 30% and 50%. Poinsettia plants need humidity in the 50% to 75% range.
The simplest way to increase ambient humidity for any houseplant is to mist it. But, given the poinsettia plant is no fan of cold temperatures, only ever use tepid water. Never use a spray bottle filled with water directly from the cold tap.
For a more hands-off approach to controlling the humidity around your plant, you could go with a pebble tray. It’s the most basic ecosystem for localized humidity. Water the plant, the water drains through the drainage holes in the pot, gravel pebbles absorb the moisture and release it back slowly.
Alternatively, you could use a small plant humidifier, which are often advertised as desktop humidifiers. These can provide just enough of an increase to the humidity the plant gets without elevating the room humidity to uncomfortable levels for you.
5 – Insufficient Lighting
It’s difficult to control the amount of sunlight any plant gets. Too much or not enough and it will have an effect on the plant’s health.
Poinsettia plants do use photosynthesis, just like every other green-leaved plant. Don’t let the red bracts fool you. The red leaves (technically called bracts) get their color from a chemical compound called Anthocyanin.
This compound gives the leaves their red hue, but it is not directly involved in photosynthesis. Only the green leaves do that. The red (or pink, purple, white, or blue) bracts change from green in response to longer nights. At that stage, photosynthesis reduces.
Leaf curl is a symptom of stress. A plant that is unable to photosynthesize, meaning it’s struggling to produce sugars for food, will need more light.
When you look at the bracts of your plant, consider the direction of sunlight and the size of the colored leaves. Sunlight needs to reach the green leaves to activate the chlorophyll for photosynthesis to happen.
In their natural habitat, these plants would grow under the canopy of trees in the warm regions of Mexico, benefiting from dappled sunlight from the canopy above. Exposure to direct sunlight for too long though, and the leaves curl in an effort to slow down transpiration.
A common reason for this happening on indoor poinsettia plants is because only one side is exposed to sunlight. The result can be one side of the plant having slightly discolored leaves, then the side constantly facing the window will be showing leaves with curling leaf tips and margins, and possibly some browning from burning on the lower green leaves.
To fix plants partially affected by either too much or too little sunlight, turn the plant to expose the curling leaves to bright indirect sunlight and they will respond.
Plant rotation is an aft-overlooked aspect of maintenance for numerous indoor plants. Leaf curling and slight discoloration are the signs the plant pot needs to be turned.
6 – Over Fertilizing
Poinsettia plants do not need a lot of fertilizer. In their first year of growth, little (if any) is needed. If you get the growing conditions right, they flower fine without any fertilizer.
When in bloom, the floral part of the poinsettia are only the tiny yellow buds in the center of the plant. Far from showy. For that reason, adequate moisture, light, temperature and humidity are enough to keep this plant thriving over the holidays.
In the second year, if you want to make a poinsettia re-bloom, fertilizer definitely helps. Applied at a rate of once monthly (diluted) from spring through to summer, then increased, then drop fertilizer levels back as the night temperatures drop, and that’s because the poinsettia is a winter bloomer.
In the second year, they need pruning, pinching, and to be fed with a diluted balanced fertilizer to make a poinsettia bloom again. That is when you can find the stresses from too much fertilizer taking its toll on the plant.
With too much fertilizer, particularly salt build-up in the soil, it slows down drainage. That leads to the leaf curl and wilting similar to overwatering, only it gets worse because fertilizer causes bursts of new growth.
What tends to happen on young plants forced to sprout too fast by applying too much fertilizer is the root zone is not strong enough to support the entire plant. Instead, baby roots feed the baby leaves on the lower part of the plant, but up top, the mature leaves struggle to get the nutrients they need.
The younger growth on the lower part of the plant gets the most nutrients, but they lack the sturdy roots and stems to support the larger leaves. The bigger leaves start to curl, wilt and droop as a result.