Why Are My Poinsettia Leaves Turning Black?

Poinsettia is a vibrant plant that is prized for its bright appearance and bloom. However, you might not be feeling festive once the leaves of your poinsettia begin to turn black.

The leaves of your poinsettias are likely to turn dark due to fungal or bacterial illnesses, particularly Alternaria leaves spots. They begin as tiny spots of brown or black that then spread and completely cover the leaf. Other causes include high temperatures and low humidity, insufficient irrigation, and the build-up of salt.

In certain cases it is possible to save your poinsettia. In other instances the problem of leaf blackening is not a solution. Therefore, prevention is the most effective method.

I’ll teach you how to determine, treat or stop each possible reason for poinsettia’s leaves becoming to black.

Causes of Poinsettia Turning Black

Diseases

Poinsettia is prone to fungal as well as bacterial illnesses. This includes bacterial canker, fungal diseases, powdery mildew scab, and many more. The three above causes extensive leaf spot damage that results in the blackening of leaves.

– Alternaria Leaf Spot

The most obvious indication of the Alternaria leavespot is appearance of dark brown or black spots on the leaves. At first, they’re tiny but, over time, they can grow to cover the entire leaf.

In extreme instances, the leaves may wilt and fall off. The disease is not usually fatal, but if not treated for a prolonged time, it can cause the poinsettia to end up dying.

– Bacterial Leaf Spots

Bacterial leaf spots are more severe and potentially fatal illness as Alternaria. If you notice yellow streaks under leaves, you could be suffering from this disease. If they’re not treated the streaks will change into red streaks that will eventually get longer and become black.

The yellow leaves and stem cankers are also signs of the illness. The affected leaves and stems eventually turn black and shrink or curled up. Dark spots of black or brown on leaves that have yellow halos is a sure indication of a the bacterial leaves spot diseases.

– Anthracnose

Also known as poinsettia scab anthracnose is a cause of dark spots that appear on the middlerib, blade, and leaves’ veins. The affected stems develop light buff lesions , which turn into black, and then cover the affected areas with a canker.

The affected leaves will begin to wilt then roll backwards and develop an angular appearance before dropping off abruptly.

Solution

The first step to take when you notice these diseases is to identify the plant affected. Then, trim away and eliminate any affected stems, leaves, or other plant material.

Next step spraying your poinsettia with a fungicidal spray on intervals of ten days or weekly. Neem oil and captan, copper-based fungicides, and horticultural oils can work.

Plant your plants in a secluded area Improve aeration and stay clear of overhead watering to stop the spread of the pathogens.

Poinsettia

Bract Edge Burn on Poinsettias

The bracts of your poinsettias are growing rapidly. They require lots of calcium as well as other nutrients to support the building of cell walls and to maintain this rapid growth.Bract edge burn occurs when calcium levels are low.

The bract margins or edges to darken or turn black. If Botrytis is present there will be tiny, necrotic brown spots along the edges of the bract. They will eventually coalesce, and then turn the entire bract into black.

Solution

Do not delay until the damage is evident. Instead give your poinsettia an injection of calcium when you notice any indications of burns on the bract’s edge.

It is possible to use an nitrate-based fertilizer to aid in root application. You can also choose an foliar spray based on calcium chloride that is applied every week for at least 4 weeks.

Heat Stress

The stress of heat can cause the leaves of your poinsettia to change color to black. Poinsettias are delicate tropical plants which begin to shrink dry out, then burn when exposed to excessive heat. This is especially true when coupled with submergeding as well as low levels of humidity.

The stress of heat can lead to an increase in temperature within the roots. This can hinder the absorption of nutrients and water and causes the leaf to change color, becoming yellow, brown or even black.

Solution

Take your poinsettia out of the heat source. This could be a heating vents, fireplaces radiators, heat vents, or even open windows in summer. Beware of areas that expose your ornaments to sudden temperature fluctuations.

Low Humidity

Poinsettias like humid, warm conditions because they’re natives to climates that are tropical. A low humidity can result in stress for the poinsettia. The leaves will change color or black, or even fall off in response to stress.

The low humidity can also speed up the loss of moisture from leaves through the process of transpiration as well as respiration. In the end, over a long period of time, those leaves on your poinsettias will become dry, flake up and appear black with scorched spots.

Solution

The poinsettia will be happy with the high levels of relative humidity. In the beginning, however, you have to get rid of the materials that are severely affected or have fallen to prevent a spread of disease.

Set up a tray of water with pebbles next to your poinsettia to increase the humidity. And, of course you could make use of an air humidifier.

Drafts

The poinsettias you plant will flourish when temperatures are in the optimal range of 60-70degF (15-21degC). However, both heat and cold drafts can expose the plant to temperature that are not within the bracket. This could cause damage to the leaf and turn leaves to black.

This is particularly true when cold drafts push temperatures lower than 60 degrees Fahrenheit (15degC). Long-term exposure to drafts that are extremely cold can cause leaves to appear burnt or wilt, then droop, and drop off. There are also signs of leaves turning yellow, brown, or faded.

Solution

  • The poinsettia isn’t a fan of drafts, so take it away from drafts.
  • Cold drafts can be caused by poorly air-conditioned rooms, AC vents entrance doors, the windows that are open during winter.
  • Get rid of hot drafts such as heating vents for space heaters, fireplaces, radiators and so on.

Sunburn

The exposure of your poinsettias to too much direct sunlight can cause scorching and harm the leaves. Sunburns can manifest as of crispy, dry leaves with dark brown or black tips. It is typically easily identifiable due to black spots that are scorched on the leaves.

Solution

Take your ornaments away from the hot place. Find a spot in which it will receive bright, indirect sunlight. Ideally you should have an east-facing window, so that it will benefit from the gentle morning sun, and also enjoy afternoon shade.

The dark leaf spots and leaves that have sunburned spots will probably not heal, so be sure to trim them off. However, leaves that are sunburned but not severely is fine, particularly when the damage to the other leaves is severe.

Root Rot and Stem Rot

The leaves of your poinsettias can become black due to root rot and stem rot. Be on the lookout for Pythium root rot, which can cause the leaves to brown, stunting, and wiping. It can cause premature flowering and dropping of leaves.

Rhizoctonia root rot can cause the leaf to blacken. It is usually spread through damaged cuttings. If the roots are damaged, the plant won’t be capable of absorbing water and nutrients, causing the leaves will become damaged and turn black.

Rhizoctonia stem rot is also prevalent in poinsettias. The rot quickly spreads to the crown as well as different parts of the plants. In the process, they slide down and feel soft and mushy to feel.

Solution

  • The root and stem rot illness is made worse by excessive watering and fertilization overflow. Beware of them.
  • First, you need to remove the affected plants and trim off dead or diseased stems and roots. If the damage from rot is severe or extensive you may want to consider propagation.
  • Treat using fungicides or hydrogen peroxide. Then repot using a new potting mix.

Insect Infestation

As with most tropical plants the poinsettia can be susceptible to a variety of bugs, such as mealybugs whiteflies, aphids and thrips spider mites, fungus and gnats. So, make sure you be sure to check the leaves particularly for whiteflies and aphids.

The majority of these pests sucking the sap from the leaves and leave brown spots that are surrounded by an orange shimmer. As time passes, the spots will grow and then turn into black.

Solution

Bring your poinsettia that is infested to the bathtub, shower, or outside. Give it a good spray of water to get rid of the bugs. Be sure to rid yourself of diseased or ill-affected parts.

It is recommended to spray your poinsettias with an insecticide spray such as Neem oil as well as miticide. Repeat this process each 7-10 days, until the signs of insect infestation have gone.

Excess Watering

The overwatering causes leaves to turn black in various ways. The first is that most bacteria and fungal diseases are caused by excessive watering (and often, over-fertilizing).

The excess water in soil can cause the roots to become suffocated and rot. They then die. This is the perfect recipe for deficiency in nutrients as well as wilting and leaf injury and all of these causes leaves to turn black.

If you notice wilting and dropping of older leaves, drooping and large black spots on the leaves, it is best to reduce the amount of water you can. (Source: Iowa State University)

Solution

  • Stop watering as soon as possible. Cut off diseased and damaged plant parts.
  • Examine the roots for signs of root decay and treat it as needed.
  • Let the top 2 up to 3 inches dry out prior to watering the next.

Over-Drying the Soil

If you let your soil dry out too much, this can cause the poinsettia’s leaves to change to black. This is because the soil is dry, making it difficult for the roots to “breathe” or absorb nutrients.

It’s a deficiency in nutrition, dehydration poor absorption of nutrients from the roots, and root damage that can eventually lead to the leaves turning black. It usually happens because of exposure to excessive sunlight, heat, and low levels of humidity.

Solution

Use indirect lighting to avoid compaction of the soil. To loosen up the soil make use of a fork or stick to break it up some. Then, mix in tiny pebbles, gravel, organic vermiculite, as well as perlite to aid in drainage.

Repot the area with new soil that is well-drained. The soil should be watered until the liquid drains out of the holes in the bottom and then drain the run-off that isn’t being used up.

Overfertilizing

If your poinsettia is growing quickly, you might be tempted to apply excessive fertilizer. This can be detrimental to the health of your plant. This is particularly evident in warmer summer and spring temperatures.

The poinsettia’s bloom will absorb more nutrients than it is able to handle. This can cause burning of the fertilizer and cause the leaves to become black.

The process also causes salts to build up in the soil. This causes the edges, tips, or even the entire leaf becoming into black.

Solution

  • Clean white salt scabs off the soil’s surface. Run the soil with water to eliminate the excess salts.
  • If the build-up of salt is extensive, you must make a new batch of the potting mix.

Lack of Nutrition

The process of feeding your poinsettias can be difficult. Too much fertilizer can result in salt burns. However the absence of potassium, nitrogen, and other nutrients can cause slow or degenerative growth.

A deficiency in nutrient levels is usually manifested as leaves turning yellow and black spots. Leaf leaves can also curl or wilt before falling off.

Solution

Begin feeding your poinsettias with half strength fertilizer for your houseplants in the early spring. Do not fertilize in the period of blooming. If you do, fertilize it every 3-4 weeks until symptoms of malnutrition go away.

Salt Build-up in Soil

Salts can begin to accumulate within the mix of potting because of the softening of water, or the poor water quality. Salts can cause leaf burns and damage to the leaves. They also affect the absorption of water and other nutrients. As time passes the leaves begin burning, turning wilting, and then fall.

The edges, tips, or the entire leaf will begin becoming black and then shrivel. Additionally, you might see white scabs on the soil’s surface, indicating salt accumulation.

Solution

Remove white salt scabs off the soil’s the surface. If the build-up isn’t overly excessive, cover the soil in water to eliminate the salts that are accumulating.

In the event of severe salt accumulation, you’ll have no other choice than to replace the potting mix using a fresh, top-quality pot mix.

Low Light

Cold draft, low light and overwatering are frequently closely linked. Photosynthesis (which assists your poinsettia in making foods) and respiration depend on exposure to sunlight.

Even if you water properly the soil can remain damp or wet for a long time due to low light. This can cause dark, yellow blotches appearing on the leaves.

Insufficient sunlight can also cause the reduction of chlorophylls, the green pigment. Without these, leaves will change color and then become black.

Solution

Place your ornament in an area where it will be in indirect, bright light.

How to Prevent Blackening of Poinsettia

  • Do not use the overhead irrigation
  • Make sure your poinsettia receives plenty of indirect, bright, or diffused light
  • Make sure your plant is kept away from cold and hot drafts
  • It is important to ensure that topsoil is dry between irrigations
  • Remove any yellow, black or brown affected parts.
  • Ideal temperature: 60-70degF (15-21degC)
  • Remove immediately any plant that is showing signs of illness or insects
  • Fertilize your poinsettia every 3-4 weeks.
Stephanie

Stephanie

Went from a bad gardener to a half-decent one over 10+ years. Super happy to share my tips and tricks with you :)