ZZ plants are known for being very easy to care for and in many instances “indestructible”.
However, like other houseplants, it can experience some problems.
If you notice ZZ plant has black spots on its stem or leaves, then it is important to investigate and figure out what is causing it.
Why does your ZZ Plant have black spots on stem and leaves? Note that black spots on stems and black spots on leaves are separate occurrences.
So, you have to treat each one as its own problem. However, in most cases, you’ll only need to deal with one or the other.
That said, the black spots on ZZ plants are often caused by pests, fungal diseases and too much sunlight.
Overwatering can likewise cause these issues to happen. And with excess moisture, you want to be extra careful as it can lead to root rot which can be fatal for the plant.
What Causes Black Spots on ZZ Plants?
ZZ Plant Black Spots on Stem Causes & Treatments
When taking about a ZZ plant with black spots it is important to specify where the black sots are occurring.
That’s because black spots on the stem of a ZZ plant have a different cause to black spots on the leaves of a ZZ plant.
As such, they warrant different diagnoses. And the corresponding treatments will also be different.
In this section I’ll be focusing on a ZZ Plant with black spots on the stem, its causes can how to treat and solve each of the problems.
Bright, Intense Light
Too much exposure to intense or strong light can cause black spots on the stem of your ZZ plant. The good news is that there’s nothing harmful or damaging about this.
And that theirs is bigger problem that develops like dryness, burning or scorching.
However, it means your ZZ plant will appreciate somewhere else where the light is not as harsh.
How to Treat It / Fix It
Unfortunately, the down side to the black spots on the stem of a ZZ plant due to too much bright or intense light is permanent.
That is, they won’t disappear nor will the stem return to its original unblemished appearance.
In fact, if you leave the plant in the same strong light environment, the black spots will keep increasing.
Therefore, it is best to move the plant to a less bright location.
Again, the black spots on the stem of the ZZ plant are just unaesthetically pleasing. But they are not harmful.
But as a plant owner, you don’t really want the black spots to increase in size or number.
So, choose a spot with medium to bright indirect light.
This is ideal for the plant in terms of growth. And it won’t cause the ZZ plant to develop more black spots on its stem.
Additionally, the plant does best when it received 8 to 12 hours of light daily.
It does prefer natural sunlight. But it will grow just fine with fluorescent lighting or grow lights if you don’t have enough access to sunlight in your home.
The thing you do want to avoid is very low light.
What ZZ plants will tolerate low light and do well there. They still need light. So, don’t leave it in dark color or dim location where light is scarce.
This will cause the plant to grow slowly and produce fewer leaves.
Outdoors, partial shade is best.
Again, avoid very strong, bright light including full sun.
Other Related Posts
- How to Save a ZZ Plant from Root Rot
- Signs of an Underwatered ZZ Plant (And How to Revive It)
- ZZ Plant Propagation from Cuttings (Stem & Leaf) and Division
- Why Does My ZZ Plant Have Yellow Leaves?
- ZZ Plant Care Instructions – How To Grow ZZ Plants
- Spider Plant Root Rot (Signs, Causes And Treatment)
Root rot happens when the ZZ plant gets too much water. As such it is never a good thing to overwater the plant.
While regular watering may be great for some water-loving plants, the ZZ plant as tough as it is, will experience a lot of problems from excess water.
Root rot develops when the roots end up in too much moisture.
As you keep adding more water, the air pockets in the soil eventually get filled with water.
This deprives the roots of oxygen which is essential to their survival.
As a result, the roots start suffocating. And the plant’s overall health, growth and function will slow down and suffer.
Unfortunately, if the overwatered condition persists, the roots will eventually die from suffocation because they never get the oxygen they need.
When this happens, the dead roots will eventually rot.
Rotten roots will not recover. Nor will they function again.
Another problem with the wet, damp environment caused by overwatering is that it encourages pathogen growth.
In this case, fungal diseases can easily develop.
Certain fungi will eat the roots. And in doing so the roots die and rot.
What’s worse is that the fungal disease will work its way up the stem. This is what causes your zz plant to have black spots on its stem.
How to Treat It / Fix It
Root rot is dangerous and can eventually kill your plant as more and more roots die then rot.
Roots absorb water and nutrients from the soil.
So, once they die, the plant has no way to get enough water or nutrients to stay healthy.
As a result, it will get weak, become underwatered and dehydrate. Additionally, it will get malnourished which is why you’ll see yellow and brown leaves.
Therefore, always be wary about excess water.
Don’t water the plant when the soil is still wet.
Wet, mucky or soggy soil is always a bad sign when you see it on the surface of the plant.
And if you suspect overwatering, always check the roots for any potential rooting. You can do this by unpotting the plant and confirming whether there is root rot or not.
If there is root rot, you’ll need to prune the rotten roots, disinfect the plant and the pot then throw away the soil.
This way the fungal infection won’t follow the plant when you repot it.
Once you’ve disinfected and treated the plant and the pot to get rid of the infection, then repot the plant.
Make sure not to water your ZZ plant at least initially to give it time to recover.
And don’t forget to adjust your watering schedule to avoid the same problem again in the future.
Stem rot is very similar to root rot. In some cases, stem rot is caused by root rot that is spreading upwards.
Here, the roots have rotted due to excess water.
As a result, the develop certain fungal disease that eats the roots and causes the rotting. As these fungi work their way up, they’ll also cause the stem to start rotting.
However, there are also instances where the stem rot occurs from fungal infections that occur on the soil surface.
Stem rot usually has the same cause as root rot.
It is overwatering and the soil becomes soggy and damp which makes the environment perfect for breeding and growing mold and fungi.
These microorganisms will attack and destroy the stem at the base of the plant where the plant does into the soil.
And this is when you see the ZZ plant develop black spots on its stem.
With stem rot, the base of the stem will be soft, unstable and easily tear off if you pull the top part of the plant.
Instead of being firm, when you feel the stem, it will be mushy, soft and slimy.
Sadly, like root rot this can also harm and even kill your plant because the water and nutrients won’t be able to move through the stem to all the leaves and other parts of the plant.
How to Treat It / Fix It
Like root rot, it is important to take immediate action if you notice stem rot.
As such, whenever you see black spots on the stem of your ZZ plant it is essential to investigate what’s causing it.
That’s because some causes need immediate attention.
Both stem and root rot fall under this category.
If you notice stem rot, immediately unpot the plant and check for root rot is well.
In case there is root rot, treat the root rot by pruning the dead roots and treating the healthy root system with fungicide or hydrogen peroxide solution to disinfect it.
You’ll also need to treat the stem rot with fungicide. This is the best way to deal with this since stem rot is caused by development of fungi in the wet soil environment.
Keep the plant somewhere warm and dry. Don’t water it for a while.
Make sure there is enough bright, indirect light and air circulation to keep things dry and prevent moisture from developing.
This will help limit the fungal growth and development.
As with root rot, it is important to adjust your watering routine and make sure you’re using soil and a pot with sufficient drainage so the plant does not end up overwatered or waterlogged.
ZZ Plant Black Spots on Leaves Causes & Treatments
In this section, I’ll move on from black spots on ZZ plant stems to the causes and solutions to black spots on the leaves of ZZ plants.
This is very different from above.
Although, in some cases the two will overlap.
Below I’ll discuss the reasons why a ZZ plant has black spots on its leaves. And for each, how to treat them.
Too much light not only causes black spots on stems of ZZ plants like I mentioned above, but it also causes black spots on leaves of the plant as well.
Note that these two events are different.
And in all likelihood, if you’re experiencing one, you won’t be experiencing the other.
The biggest difference between black spots on ZZ plant leaves and the stems is that the former is more dangerous.
While the black spots on the ZZ plant’s stems are harmless and more of an aesthetic nuisance, the black spots on leaves of the ZZ plant can damage the plant.
That’s because these happen when the plant sits in too much strong or intense sunlight.
As a result, the harsh rays of the sun can scorch its leaves leaving them with black spots. These black spots are actually burn marks.
And the longer the plant stays in this environment or the stronger the rays get, the more damage the leaves will sustain.
The problem here is that as the leaves get damaged and burn they will cease to function or experience reduced functionality.
That means they won’t be able to absorb the same amount of sunlight from the sun.
So, the plant won’t have enough light to use for photosynthesis.
What happens then is the plant’s growth slows and it produces fewer leaves and gets weaker since the end product of photosynthesis is energy.
How to Treat It / Fix It
Move the plant to a less bright spot.
Do this when you see your ZZ plant develop black spots on its leaves. You want to prevent these from spreading and appearing on more leaves.
Sadly, once the black spots on ZZ plant leaves appear, there’s no healing or reversing them.
They are permanent.
So, you will need to prune the entire leaves or trim off the sections of the leaves that have been damaged.
Make sure to pick a well-lit location with no direct sunlight.
The ZZ plant is a tropical plant that is native to the forest. There it lives under the canopy created by the huge, tall trees.
As such, it cannot tolerate more than 1-2 hours of direct sunlight.
Instead, it prefers indirect, dappled, filtered or diffused light. Here, go with medium to bright light.
Overwatering is another reason why your ZZ plant can have black spots on its leaves.
In this case, it is overwatering and waterlogged soil that causes the problem.
And you’ll end up seeing curling leaves with black spot.
Why does this happen?
Overwatering the plant causes the soil to get wet. And as more water comes in the oxygen in the potting mix is reduced.
In very waterlogged soil, there is no more oxygen for the roots to breathe.
The problem is that roots need oxygen and water to survive. Too much or one or another will result in problems.
Too much water means the roots end up suffocating as they drown in liquid.
This prevents the roots from functioning at 100%. So, you end up with a plant that is not absorbing as much water or nutrients through its roots.
As a result, the leaves won’t receive as much moisture as they normally do.
When this happens, you’ll start seeing black spots on ZZ plant leaves. The leaves will likely curl in an effort to reduce water loss from transpiration.
The other possible reason for ZZ plant black spots on leaves is fungal infection.
This can happen when you water over the plant.
In doing so, you wet the entire plant including the leaves.
If the leaves stay wet or have water spots that don’t dry for hours at a time, the wet conditions increase the risk of fungal infection.
Some of these fungal diseases will show up as black spots on the leaves of your ZZ plant.
How to Treat It / Fix It
Be careful of how you water and when you water.
Make sure that you don’t water the plant when the soil is still moist or wet. Instead, wait for part of the soil to dry between waterings.
Overwatering causes many different problems for plants.
Thus, always check the soil before watering the plant.
With the ZZ Plant allow the top 2-3 inches of soil to completely dry before adding more water. Stick your finger into the soil and check the soil at that depth.
If the soil 2-3 inches from the surface feels dry, then it is time to add water.
But never add water before that time.
By following this simple rule, you’ll be able to reduce the risk of overwatering the plant.
In addition to knowing when to water it is also important to know how to water.
Here, don’t water over the plant where all the leaves end up wet. If you do this, you’ll need to pat down the leaves with a dry towel, so they don’t end up staying wet for long.
Otherwise, the wet leaves will increase the risk of fungal infections.
Instead, water directly onto the soil.
Finally, choose a pot with drainage holes. This will allow excess moisture to drip out of the container.
Using the right kind of soil and pot will help prevent waterlogging.