Why Do Coneflowers Turn Black? (Explained)

by Alex Kountry
Updated on

Coneflowers are hardy plants that are resistant to drought and heat. This and their colorful foliage makes them a favorite with many gardeners.

Coneflowers can be planted in a lot of places and they help attract pollinators to the garden.

Although coneflowers are strong flowers, they also have diseases that affect them and when your coneflower starts to turn black, it indicates there is a problem somewhere.

Leaf spot diseases including Alternaria and bacterial leaf spot ate the causes of coneflowers turning black.

Your coneflowers need to stay healthy so you can enjoy your garden in spring. Today we will discuss why coneflowers turn black and other related issues.

Why Do Coneflowers Turn Black?

You might have noticed your coneflower leaves changing from green to black in patches. This means your plant is no longer healthy and has already been infested by a disease.

There are two major causes of blackening coneflower foliage and they include Alternaria and bacterial leaf spot diseases. 

Alternaria leaf spot begins as tiny black or brown spots on the plant’s leaves.

These develop pale centers and become oblong as they expand. After expansion, the centers of the spots become lighter.

These spots can sometimes even cover the pores and vines of the plant. Along the midrib of younger leaves, the spots can be observed. 

Bacterial leaf spot, as the name suggests, is caused by bacterial organisms. The symptoms of this disease differ slightly from those of Alternaria leaf spot disease.

This disease also has dark brown or black patches just like in Alternaria. This location is frequently surrounded by a golden halo.

Because these patches do not travel on the veins, their spread is limited.

You should always watch out for these two diseases and once they have gotten to a serious stage, they can kill the plant.

Treatment for these two diseases is often done by spraying fungicide on the plants.

Mulching, sanitary habits as well as crop rotation are further methods that can be used to treat these leaf spot diseases.

Of course, prevention in the first place is always the best option and the defense against these is to have a healthy plant.

Here is an article I wrote about do coneflowers attract bees?

Should You Deadhead Coneflowers?

Deadheading, or clipping of wilting flowers from a plant, helps to redirect the plant’s energy toward the healthy root and leaf growth instead of seed production.

It also encourages flower blooming for plants that are not doing well as well as reblooming in a new season. 

Some species of coneflowers such as the Yellow and Purple do not require deadheading. 

However, some like the Black-eyed Susan must be deadheaded to ensure they grow flowers consistently throughout the season.

Removing the spent flowers also reduces the rate of self-seeding in the plant. 

Make sure to deadhead plants before the seed heads ripen if you don’t want them to spread all over the garden.

You can leave some of the seed heads on the plant so it can serve as food for birds during winter.

Removing the flowers as soon as they finish flowering also helps to keep the garden looking neat and tidy.

Why Are My Coneflowers Losing Color?

Coneflowers are known for their bright colors which bring a cheer to the environment, especially after the drab look of winter.

Although coneflowers fading might be attributed to the plant being unhealthy, in most cases it is often not something to worry about.

Pollinators such as bees are attracted to flowers due to their bright colors.

However, after pollination, the flowers no longer need to attract the bees and as such, they begin to fade.

Science has not figured out how pollination is related to flower fading but it is a part of the natural progression of the plants. 

Your coneflower can also be losing color if it is stressed or not getting enough sun. Coneflowers like to get full sun with about 6 to 8 hours of sun.

if they do not get as much sunlight as they need coneflowers will start to fade. If your plant is looking unhappy in its correct location, you might want to change its position so it can start shaping up. 

Coneflowers can also look faded when they are stressed, especially when they have just been transplanted.

Do ensure you always keep an eye out on your plants to keep them healthy all the time with their color popping.

Also check out this article I wrote on are coneflowers invasive

How Do You Make Coneflowers Grow Better?

Coneflowers are pretty easy to care for and after their first growth season, they develop into strong and leggy plants. If you have been having problems with your coneflower here are a few tips to help you grow them better:

  • Place thin layers of organic manure and mulch around the plants to help retain moisture and discourage weed growth.
  • When planting, ensure that your soil is rich in organic matter and add fertilizer from time to time.
  • Coneflowers require very little water. Add water to your coneflowers only if the season is exceptionally dry or if they are newly planted.
  • To extend the blooming period, remove spent flowers. Reduce stems to a leaf close to a bud.
  • In late autumn in colder regions, spread mulch lightly around plants.
  • When they wilt or after a frost, prune stems to the soil level. To encourage self-seeding, prune in late winter. When sprucing up the garden in late winter or early spring, prune back the shrubs.

With these steps, your coneflower will definitely come out stronger and more colorful.

What Are The Common Coneflower Problems?

Coneflowers are quite strong flowers which are rarely affected by diseases but this doesn’t mean they will not get affected if not properly cared for.

Outlined below are 5 of the common coneflower problems while they are growing:

  • Powdery Mildew

Powdery mildew is sometimes caused by overwatering coneflowers. Powdery mildew comes up when there is excessive moisture and a lack of airflow in the soil. This is easily avoidable by ensuring adequate air circulation and spacing, as well as minimizing moisture.

  • Stem Rot

Stem rot often happens when you overwater coneflowers. The plants are drought-tolerant and require less water than the majority of other plants.

  • Aster Yellow

 Aster Yellow is typically transmitted by insects and poor growing conditions, which render plants more vulnerable. 

When plants are infected with aster yellows, they exhibit deformed flowers, stunted growth, and may eventually begin to die. Infected plants must be removed and eradicated.

  • Aphids

Aphids are a common problem with coneflowers. Green peach and black ambrosia aphids are especially nasty when they attack the plants.

These pests harm coneflowers by sucking the sap from the leaves and stems and leaving behind a sticky substance known as honeydew. They are responsible for spreading diseases like powdery mildew.

  • Fusarium Wilt

Fusarium wilt or blight is a common disease caused by Fusarium oxysporum. It is termed wilt since one of the earliest symptoms is wilting during the day.

Additionally, leaf margins can develop dark spots. The leaves turn yellow and die in their final stages.

When Do I Transplant Coneflowers?

Coneflowers are best transplanted or relocated in early spring, when the soil is warming and softening.

Additionally, they can be transplanted in early autumn, when temperatures are cooler and the sun is less intense than in the summer. 

Coneflowers should not be transplanted during the summer. After approximately three or four years of growth, you can divide your coneflowers and transplant them.

Or, you can frequently move an entire plant from one location to another. 

You should be able to replant your coneflowers without incident if you take care to do so at the proper time of year and are able to obtain a sufficient quantity of the healthy root system for a healthy transplant.


Coneflowers also get diseases just like other plants. Gardeners have experienced coneflower foliage turning black.

This is caused by the presence of leaf rot diseases namely Alternaria and bacterial leaf spot.

By taking proper care of the coneflowers you can help them be healthier and grow better.

Do you have coneflowers in your garden? Then utilize the tips in this article to get the best out of your plants.

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About the author

Alex Kountry

Alex Kountry is the founder of HayFarmGuy and has been a backyard farmer for over 10 years. Since then he has decided to write helpful articles that will help you become a better backyard farmer and know what to do. He also loves to play tennis and read books