10 Reasons Your Zinnias Are Turning Brown or Dying

Zinnias are some of the most beautiful flowers you can add to your garden. But what happens when they suddenly start turning brown, or start to die off? There's a number of different reasons this can happen. In this article, gardening and flower expert Taylor Sievers examines 10 different reasons your zinnias are dying and how you can fix it.

Zinnias Turning Brown

Zinnias have been a staple in backyard gardens for many generations. They provide delightful color and cheer to a cutting garden, and they bring much-needed pollinator insects to the vegetable patch. Because they’re beautiful, tough plants that thrive with little water in the heat and full sun, they’re definitely a great addition to any garden plant lineup. 

However, there are a few factors that may influence your zinnia patch, and if you’ve found yourself in the past watching your dazzling zinnias turn brown and icky, then you may be experiencing one of the few problems with zinnias.

Read on to learn more about the reasons your zinnias may be turning brown or dying and how to prevent some of these problems in the garden. Let’s jump in and look at each reason, as well as how to solve them in more detail!

Why Your Zinnias Are Dying

Now that you know a little bit about zinnias and why they’re so beloved, let’s dive into the reasons why your zinnias may be struggling in the garden. There are a number of different reasons this happens, and each of them typically has a different treatment. Depending on the cause for the browning of your leaves or flowers, your plant may or may not be recoverable. Let’s take a look at each reason, and how you can treat them.

Alternaria Leaf Spot or Blight 

Blight on Yellow Flower
Spots that are reddish with white-gray centers are a sign of blight.

If you begin to notice small, dark, circular, reddish spots with white to grayish-white centers on the leaves of your zinnias, your plant may have been infected by the fungus Alternaria zinniae. Unfortunately, leaf spots affect many different types of flowers.

These spots will expand and become irregular in shape and turn dark red, brown, or purplish in color. You may notice dark, concentric rings on the inside of the infected lesion. The spots may eventually become holes as the decaying plant tissue falls out.

Seriously infected zinnia plants will have leaves that turn brown and shrivel quickly from Alternaria leaf spot, and brown lesions can form on the stems. If lesions are bad enough on the stems they can cause girdling of the stem, where the top portion of the plant will subsequently wilt and die off due to the vascular system being cut off.  

How to Fix:

Fungal infections in Zinnias can be treated if they are mild or moderate. You can use horticultural oils to treat the problem, which includes neem oil, or jojoba. A commercially available fungicide may also be an option if weaker options like neem oil don’t fix the problem.

Powdery Mildew 

Powdery Mildew on Red Garden Flowers
Improper watering can cause too much moisture, which is ideal for growing a fungus, like powdery mildew.

Powdery mildew is caused by a fungus, and this disease is very common on zinnias late in the season. A white, powdery growth will form on the leaves, eventually spreading to the stems and flowers. Powdery mildew usually works its way up the plant.

Severely infected leaves will begin to turn brown and die starting at the base of the plant. Heavily-infected plants will lose vigor and cease growth.  

How to Fix:

Similar to blight, powdery mildew can be treated with commercially based fungicide, or neem oil. But it’s best used early in the season before powdery mildew has a chance to form. If your plants are heavily infected, you may have no choice but to pull them and replant.

Cercospora Leaf Spot 

Cercospora Leaf Spot on Zinnias
Another fungal disease that thrives in moist conditions is Cercospora leaf spot.

Cercospora leaf spot is very similar in appearance to Alternaria leaf spot, and therefore can be confused easily. Oftentimes, both Alternaria leaf spot and cercospora leaf spot can occur at the same time. 

Cercospora leaf spot is caused by the fungus Cercospora zinniae, and the spots will be fairly large, round, dark purplish with gray to gray-white centers. The plant tissue may fall out of the centers as decay progresses. Severely infected leaves will turn brown and shrivel rapidly. 

How to Fix:

Leaf spot is also a fungal infection treated by a commercially based fungicide. Neem oil can also work. Leaf spot is typically easier to treat compared to other fungal infections, and if treated early, your plant will have a better chance of survival.

Lack of Water 

Flower Dried Out and Turned Brown Due to Lack of Water
One of the more obvious reasons zinnias turn brown is due to not getting enough water.

Even though zinnias do not require a lot of water, there is a point where they do need some water. If you’ve been experiencing drought conditions and your zinnias are starting to die, it’s likely due to a lack of water.

One of the first signs that your plants aren’t receiving enough water is wilting. The leaves will droop and shrivel and, if the situation isn’t corrected, they will begin to turn brown and die. Wilting can be corrected rather quickly if the plant is given ample moisture to recuperate.

If the plant has reached the point at which it’s turning brown and dying due to lack of water, it is likely too late to revive the plant. Even if the plant does survive, drought stress can cause long-lasting and permanent effects on a plant and its future growth. 

How to Fix:

Start a proper watering schedule. As long as the plant isn’t turning brown, then adjusting your watering schedule should bring them right back with a little time. If your zinnia’s leaves are brown and crispy, it’s likely too far gone to save.

Waterlogged 

Orange Flowers Turning Brown From Too Much Water
Too much water can also cause problems for zinnias, ultimately killing them.

More commonly, zinnia plants can also suffer when they’re waterlogged. What does this mean? It means the soil is either not draining or there has been too much water in the soil. While water is important for plants, plant roots also need oxygen.

In waterlogged conditions, the soil pore space (the space between soil particles) is entirely full of water, and therefore no or very little oxygen is available to the plant roots. Due to lack of oxygen, the roots will begin to wither, and you’ll begin to notice the plant leaves turning brown around the edges.

If you notice this happening and you’ve been watering your zinnias regularly–stop. Let the soil drain. Always choose a well-draining site in your garden to plant your zinnias to prevent issues from waterlogged conditions. 

How to Fix:

Too much water can also be a problem, so the solution here is also simple. Don’t water them too much, or change the soil so it’s more well-draining. Basically, when a plant is waterlogged, it’s being drowned. So this is typically an easy fix to just adjust y our water schedule.

Frost 

Dead Flowers With Frost
These heat-loving flowers will not survive a frost.

Zinnias love the heat. They are a summer-loving annual! So, like many annuals, they do not survive most winter temperatures. You’ll notice that your zinnias will bloom well into the Fall, but then suddenly the first frost of the season hits.

When that happens, you’ll notice your zinnias will suddenly turn brown overnight due to the freezing temperatures. Sometimes they’ll pull back out of it if the frost wasn’t severe or if another frost doesn’t come along for a while, but more than likely your zinnias are toast for the season. All good things must come to an end, right? 

How to Fix:

There’s no real way to prevent zinnias from dying off in the winter. The best way to avoid severe frost damage is to cover the plants in the winter when it gets too cold. But your flowers are not typically going to bloom past autumn, depending on your climate.

Setting Seed 

Seed Head of Garden Flower
Once zinnias flower, they will naturally turn brown and die.

Again, zinnias are annuals. This means that they complete their life cycle within one year or one season. The seeds will germinate in late spring, the plant will begin to bloom in summer, and then once the plant has bloomed its little heart out, it will begin to set seed.

As gardeners, we can delay this by deadheading the faded flowers to promote new blooms, but sometimes we may miss a few blooms or maybe we just aren’t concerned with that type of maintenance.

You’ll notice the flower petals will fade away and turn brown and crunchy until the whole flower head has become ugly, crunchy, and brown. No worries! Simply take this faded flower head in your hands and squish it gently between your fingers. You’ll find hundreds of brown zinnia seeds. This is one of the few times your zinnias turning brown is a good thing! 

How to Fix:

Setting seed is part of the Zinnia’s life cycle. Since they are annuals, they complete their life cycle in a full year, so there’s no real fix for this. But when it happens, it’s actually a good thing, and can help you start more blooms in the spring!

Bacterial Leaf Spot 

Dying Flower
Bacterial leaf spot is yet another disease that can be avoided with proper watering.

The bacterium Xanthomonas campestris is the culprit behind this leaf disease. At first, very small, translucent, and widespread spots will appear with broad yellowish halos around them. If environmental conditions are wet, the spots will slowly begin to enlarge.

The spots will then become irregularly circular or angular in shape with a reddish center. The lesions may merge to form large dead areas. Small brown spots may form on the petals of the flowers, with severe infection resulting in disfigurement and decay of the entire flower head.  

How to Fix:

Bacterial leaf spot can be treated in the same way a fungus is. You can treat it with neem oil, fungicide, and even a baking soda solution, which is more natural and usually more readily available than other lest cost-effective options.

Aster Yellows 

Deformed Flower With Aster Yellows
If your zinnias are malformed or small, they may be suffering from aster yellows.

Aster yellows is caused by a phytoplasma that is transmitted by leafhoppers. This organism affects members of the Asteraceae family, of which zinnias are a part. Symptoms include small, malformed flowers and yellow, stunted growth.

As the infection continues, the plant will begin to die back and turn brown. The plant will never recover after infection. If you notice these symptoms, immediately remove the infected plants and either burn or bury them.  

How to Fix:

Controlling an aster yellow infection is extremely difficult. If your zinnias have a case of Aster yellow, you will likely need to remove the infected plants from the area. This disease is highly contagious, and once it starts to take off, there’s little point in trying to remedy it. There is no cure, or treatment for aster yellow. Your only option is to remove the plant and hope it does not spread to others.

Root and Stem Rot 

Dried Out Flowers From Root Rot
Rotting in the roots or stem will eventually kill the plant if not taken care of.

Soil-inhabiting organisms like Pythium, Rhizoctonia, and Fusarium are to blame for root and stem rots. The symptoms of root and stem rot on plants will occur first at the base of the plant as dark brown, gray, black, or red spots.

Beneath the surface of the soil, the tips of roots will begin to decay, and the plant may wilt, die back, or lose vigor as a result. Stems may become brown and squishy or the inside of the stem may begin to turn brown.

Once symptoms above the soil line have begun to occur, it is often too late for the plant to recover. Root and stem rots occur most often in the cool Spring weather under excessively moist or waterlogged conditions. 

How to Fix:

Root rot is difficult to treat. Once zinnias pass a certain threshold, it’s time to remove the plant entirely as root rot can spread. If it’s just a single plant, the best way to treat it is to clean the roots of the plant thoroughly with water. Remove any possible soil that the infected areas may have touched. Treat the roots with a fungicide and replant them.

Preventing Zinnia Diseases

Bright Pink Flower on a Sunny Day
There are a number of ways to keep zinnias bright, happy, and healthy.

There are several fungicides on the market that are labeled for some of the diseases mentioned above, but by utilizing or promoting a few of these practices, your zinnia patch will be nearly disease-free and, in general, healthy. 

Seed Selection

Purchase healthy, disease-free seed from a reputable seed company. Some of these diseases, like Cercospora leaf spot and Alternaria leaf spot can be transmitted by seed that was collected from infected plants.

Soak Your Seeds

If you’re unsure about your seed, you can either soak in a 10% bleach solution for 2 minutes to kill bacterial leaf spot organisms, or you can soak seeds in hot water 30 minutes prior to planting to kill Cercospora and Alternaria organisms. Make sure to rinse the seeds in cold water and dry them before planting them. Do not use the hot water method if you’re using old seed.

Properly Space Plants

Space your plants further apart to promote air flow through your flower bed. Increased air flow means that any dew or moisture on the leaves will dry out faster, thus reducing incidence of disease.

Choose a Well-draining Planting Site

Choose a well-draining site to plant your zinnias. Waterlogged conditions not only reduce oxygen available to the root zone, but they also increase the likelihood of your plant being infected by root rot organisms. If your site is not naturally well-draining, you can promote drainage by amending the soil with compost or creating raised beds.

Water at the Base

Always water at the base of your plants instead of overhead. The less standing water on your plant foliage, the better. Too much moisture in the plant canopy can promote the spread and infection of disease.

Choose Disease Resistant Varieties

Choose disease-resistant varieties. Plant breeders have been working hard over the years to breed zinnias that are specifically resistant to common diseases of zinnia. You can find disease-resistant varieties listed in seed catalogs or on the seed company’s website.

Remove Infected Debris

Remove and burn or bury infected plant debris from the garden during or after the end of the gardening season.

Remove Weeds From Your Garden

Weeds can be hosts for all sorts of viruses, harmful insects, and other organisms, so it is best to keep a weed-free garden. Not only are they carriers or hosts, but they compete with your garden plants for sunlight, nutrients, and water as well.

Final Thoughts 

Zinnias are a great flower for the home garden due to being relatively low maintenance and pretty as well! Unfortunately, even though zinnias are easy to care for, that doesn’t mean that disease, poor vigor, and plant loss won’t occur. Hopefully, you’ve learned the main causes of why your zinnias may be turning brown and dying and what to do about it in the future to prevent further problems.  

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