7 Reasons For Zinnia Leaves Turning Yellow (Solutions Included)
This article guides you through the causes and solutions for zinnia leaves turning yellow, all based on scientifically backed research papers.
Zinnias are amazing plants that are mainly grown for bright flowers. However, the random yellow leaves will draw attention away from the flowers which is not a good thing.
As a plant owner, it is your responsibility to understand what’s wrong with your plant. In this article, we will dive deeper into the causes and solutions for zinnia leaves turning yellow.
Yellowing of zinnia leaves can be caused by several conditions that come under either mistake in care or plant diseases. These include nutrient deficiency, lack of water, damaged roots, lack of light intensity, poor drainage, and pest, and microbial infestation. Find out what is the real issue to take action to prevent the problem from progressing.
Let’s take a look at each of these causes in detail along with possible solutions to fix and prevent the issue.
1. Nutrient Deficiency
Since Zinnia plants are quite hardy in the majority of outdoor conditions, nutrient deficiency is the number one reason for the yellowing of leaves.
According to James Schuster, an educator from the University of Illinois Extension Horticulture, lack of iron is the main culprit of zinnia leaves turning yellow. Iron deficiency triggers chlorosis, a condition in plants that occurs when a majority of leaves lack the required amount of chlorophyll (green pigment).
Although iron deficiency is the main cause, magnesium, zinc, and nitrogen deficiencies can also trigger yellowing of leaves.
The best way to fix the nutrient deficiency in zinnia plants is to add a slow-release fertilizer to the soil so that the plants will get a continuous supply of nutrients over some time. However, if you prefer organic fertilizers instead of chemical ones, we highly recommend adding bulky organic manure, kitchen waste, and vermicompost.
2. Lack of water
If your zinnia is getting the correct amount of nutrients, then the next thing to check is how much water the plant is getting.
Even though both lack of water and too much water can cause zinnia leaves turning yellow, we’ll be focussing on the lack of water in this section.
You already know that just like animals, plants also need water to generate energy. When they are not getting enough of it to satisfy the requirements, plants tend to conserve energy which in turn results in yellow, curly, and droopy leaves.
In such cases, adding water is the only thing you can do. When watering, be sure to properly soak the plant’s roots rather than providing it with frequent, little hydration.
It is always recommended to do a moisture test on your zinnia soil before every watering because you don’t want to drown it either. If the top 2 inches of the soil are dry to touch, it’s time to water.
3. Damaged roots
The roots of a zinnia plant act as the veins, carrying water and other nutrients from the soil to every part of the plant. The fact that damaged roots will cause the plant process to stall and cause symptoms to appear in leaves is pretty much common knowledge.
Zinnia roots can be damaged due to various reasons like root rot, root bound, pests, etc. However, the most common one is root rot due to overwatering.
Root rot due to overwatering is nothing but the roots of your zinnia plants decaying due to too much water in the soil.
Overwatering your zinnia plants will cause the soil pockets to get filled with water instead of air, according to a study that was published in the Clemson Cooperative Extension. This in turn makes the zinnia plant’s root deprived of oxygen.
The chlorophyll in your zinnia plant’s leaves begins to degrade when their roots are rotten in water without access to oxygen, according to the Ask a Biologist column of Arizona University. As a result, the leaves start to turn yellow, then brown and dry.
To fix the damaged roots, first, uproot the plant from the ground if possible (depending on the size of your zinnia plant). Analyze the conditions of the root, remove all the damaged roots and treat the healthy roots with good pesticides and rooting hormones.
Also, make sure that you are not overwatering the plant to prevent root rot from happening in the future.
4. Lack of light intensity
If you are 100% sure that underwatering or overwatering is not a cause of your zinnia leaves turning yellow, then the next one to analyze is the amount of light your plant gets daily.
Most indoor plants turn yellow when the light is too much. However, in the case of zinnia, the opposite is the cause. They turn yellow when they receive very little light.
Zinnia plants are considered to be very hardy outdoor plants that grow just fine in the majority of hot and tropical regions (USDA 3-10). And, these plants love bright light like anything!
According to many scientific research papers, zinnia plants thrive when it gets atleast 6 hours of direct sunlight every day.
When a plant does not get enough light, the rate of photosynthesis decreases. In such cases, all of the chlorophyll content is not used by the leaves and those pigments start to break down over time resulting in yellow leaves.
To fix the light issues, make sure that your zinnia plant is kept at a spot where it gets at least 6 hours (8 hours preferred) of full sun every day.
5. Poor drainage
Poor drainage is not the direct cause of zinnia leaves turning yellow, but it causes other conditions that trigger color change.
Poor drainage can be either due to poor soil mixture or bad pot.
If your zinnia is kept in a pot, then drainage holes play a very important role in its watering. Inadequate holes artificially create a situation like overwatering and damage the roots. Similarly, cloggy or damp soil will suffocate the roots and trigger root rot issues which in turn causes yellow leaves as symptoms.
To fix the poor drainage problem, the ideal way is to provide the best soil mixture for your plant which has good aeration and water draining capability. Also, make sure that the pot you use has enough drainage holes to discard excess water.
6. Pest infestation & diseases
This is one of the very commonly seen causes for zinnia leaves turning yellow, however many gardeners simply neglect this.
Yellowing due to pest infestation does not look like a typical yellow shade in leaves, instead, it will be in the form of yellow and brown spots. It is caused by tiny insects, bugs, flies, etc.
The leaves of your plants are seriously harmed by these tiny sap-sucking insects. They typically settle down beneath the leaves and begin absorbing the nutrients from them.
Within a short period, an army of mealybugs or aphids will be against you! These insects reproduce very quickly! All of the typical leaf issues, including curling, yellowing, brown patches, drying, and wilting, will be caused by these insects.
Other than visible pests and insects, invincible microbes like viruses, fungi, and bacteria can also trigger the yellowing of zinnia leaves.
The commonly seen zinnia diseases that result in the yellowing of leaves are,
- Zinnia Yellow Net Disease
- Alternaria Leaf Spot
- Cercospora Leaf Spot
- Bacterial Leaf Spot
- Aster Yellows
The only way to fix a zinnia plant affected by the disease is to treat them with insecticides, pesticides, and fungicides depending on the cause of the disease. These solutions include insecticidal soaps, horticultural oils, Chlorothalonil, copper-based fungicides, etc.
7. Natural yellowing
It is very common for a perfectly healthy plant to turn some leaves yellow before and after a rigorous blooming season. There is nothing to be concerned about because it is very natural.
If your zinnia does not show any other problems mentioned above, then natural yellowing is the only cause. Since it is a natural process, there is nothing you can do to prevent it.
However, if the yellow leaves are bothering you, simply prune them with sterilized shears or a pair of scissors.
Zinnia Leaves Turning Yellow – Frequently Asked Questions (FAQs)
If you see yellow leaves in a perfectly healthy zinnia plant for the first time, it is natural to have many questions and doubts. In this section, we will be answering some of the most frequently asked questions on the internet regarding zinnia yellow leaves.
Why are my zinnia seedlings turning yellow?
The most common reason for zinnia seedlings turning yellow is either too little water or too little light. A mature zinnia plant may tolerate dry soil or shade occasionally, but for seedlings, a continuous supply of moisture is highly required for healthy growth.
Can too much sunlight cause yellow leaves in zinnia?
According to expert gardeners, there is no such thing as “too much sunlight” in the case of zinnia plants. They are supposed to be outdoor plants that take full sun all day without any issue. However, if the plant is not getting other parameters like enough water or humidity, leaves might turn yellow very quickly in full sun.
Will yellow leaves in zinnia turn green again?
A zinnia plant can’t turn its yellow leaves back to green. Chlorophyll is the pigment that gives green color to zinnia leaves. When the leaves lose chlorophyll, they turn yellow. The plant abandons the leaf after it stops producing chlorophyll and starts utilizing any remaining nutrients in the leaf. As a result, yellow leaves mostly turn brown and dry up.
Zinnias are hardy outdoor plants in many zones, but their leaves can turn yellow if the environment is not ideal.
The yellowing of leaves is not a fatal issue in itself, but it is one of the commonly seen early symptoms of many severe plant problems and diseases like root rot, bacterial wilt, etc.
So, if you are seeing a couple of zinnia leaves turning yellow, then it’s time to analyze the environment it is in. Check for problems like lack of water, nutrient deficiency, pest infection, etc, and fix them on priority so that the probability of reoccurring is eliminated.
To back up the information we provide in our articles, the Plantials team only uses high-quality sources published in peer-reviewed university or scientific research journals.
- Zinnia Yellow Net Disease, Food & Agriculture Organization Of United Nations.
- First Report Of Ageratum Yellow Vein China Virus Infecting Zinnia Elegans In Vietnam, APS Journals.
- Identification Of Zinnia Leaf Curl Virus Infecting Zinnia Elegans In India, Arunachal University Via Researchgate.
- Diseases Of Zinnia, Poznań University Of Life Sciences Via Researchgate.
- Yellow Leaves Can Indicate Plant Problems, University Of Illinois.
- Yellow Leaves In Landscape Plants, University Of Florida.
- Zinnia Insect Pests & Diseases, Home & Garden Information Center, Clemson Cooperative Extension.