5 Causes of Black Spots on ZZ Plant Stems [Fixing Guide]

Your ZZ plant is developing black spots on its stem and that doesn’t seem to stop?

ZZ plants are very much welcomed as a houseplant because they are very easily maintained. But sometimes some conditions make black spots on their stem that are very hard to get rid of.

If you don’t start treating these spots immediately the plant can become very weak and even it can die. But, to fix this problem you have to know what is causing the spots and how you can solve it.

So why are the ZZ plants having black spots on their stem?

Too much sunlight, Overwatering, Root rot, Stem root, and Leaf spots are the 5 reasons that can cause dark or black spots on your ZZ plant stem.

Don’t worry! Solving this issue is not going to be very hard for you. Because this article has got you covered with all the do’s and don’ts so that you can treat them efficiently.

So let’s get started-

What Causes Black & Dark Spots On ZZ Plant Stems

How To Fix Black Spots On ZZ Plant Stems

1. Too Much  Light

There are a lot of plants that like plenty of sunlight. But the ZZ plant is not one of them. They need very little sunlight to be naturally beautiful. 

So, If you let your ZZ plant in scorching bright sunlight then it will develop black spots on the stems. So, whenever you see your ZZ plant has black spots on the stem the first thing you need to check is the amount of sunlight they are getting.

Control Measure

If you have figured out the black dots on your ZZ plant stem are because of bright sunlight then immediately move them to another place where the light is low. In this case, the dark spots on the ZZ plant stem will take a very long time to disappear but your plant will not get new spots anymore.

But here is the catch, You also have to make sure the ZZ plants get at least 4 hours of sunlight everyday. Otherwise, their leaves will turn yellow and brown and fall off from the plant.

Since they are a bit sensitive to sunlight, it’s better to give them indirect light. For this, you can place them a few feet away from the window so that they are not directly exposed. 

2. Overwatering

ZZ plants don’t need much water. They don’t like their roots to be wet. If you overwater them the stems will get dark spots and the leaves will be turning yellow and wilt. 

Control Measure

Water them when the soil surface is dry. Make enough drainage holes on the pot so that excess water can drain easily from the pot. Otherwise, fungal problems like root rot and stem rot will occur

It’s hard to tell how much to water the ZZ plants because it depends greatly on soil condition, pot size, and weather conditions. You can use a moisture meter to know how much water your ZZ plant need (Our pick: Atree Soil Soil Tester Kits with Moisture, Light, and PH Test for Garden).

3. Stem Rot

The next thing to check is whether your plant has stem rot. If you have kept your ZZ plants in low light but still there are black spots on the stem then it’s a fungal disease. Stem rot is caused by a soil-borne fungus. It occurs if the stem is constantly wet or in waterlogged condition. 

In stem rot, the ZZ plant stem shows dark spots, especially near the soil surface. It’s really important to fix the stem rot as soon as possible. Because without timely treatment the plant will gradually die.

Control Measure

First of all, you need to check the plant for fungal symptoms. If the stem near the soil is slimy or mushy with dark spots then, you can be sure of stem rot. In addition, there will be a foul smell near the soil surface. 

Stem rot is a fatal problem for your ZZ plants. So, without any delay get the best kind of fungicide that is suitable for houseplants (Our Pick: Bonide Copper Fungicide).

It’s really important to use a good quality and safe fungicide because you will be using them inside your home. Always follow the label instructions carefully while preparing the fungicide otherwise you will end up hurting your plant. 

Repot your ZZ plant in another well-draining potting mixture very carefully. And be very alert about watering. Because overwatering is one of the main causes of stem rot. While watering do not wet the leaves and stem. Just water at the base. 

Don’t forget to keep drainage holes in the pot so that extra water can easily drain out from the soil. Water only when the soil gets dry.

Try these homemade fungicide spray recipes for safer control of stem rot 

#Recipe 1:-Cinnamon Spray Recipe

Ingredients:

  • 1 Tablespoon of Cinnamon
  • 1 Liter of water

Steps:

  • Mix water and cinnamon together and shake very well
  • Let it sit overnight or at least for 5-6 hours
  • Strain the mixture with a fine cheesecloth
  • Put the mixture into a spray bottle 
  • Store the leftovers into a separate bottle 
  • Spray it on your ZZ plant leaves and stem twice a week until the problem is solved

Recipe 2:-Baking Soda Fungicide Recipe

Ingredients:

  • 1 teaspoon of baking soda
  • Half a teaspoon of dishwashing liquid
  • Half a teaspoon of any cooking oil 
  • 1 liter of water

Steps:

  • Add baking soda and cooking oil to a mixing bowl and add the liquid soap
  • Then mix with water and stir slowly
  • Then pour it into the sprayer.
  • Spray on your rosemary plants up to twice a week.

Note: Before applying these homemade fungicides to the whole ZZ plant try it on a small scale.Because sometimes the homemade solution can cause irritation to the plant. After applying a small amount, wait for some time. If there is no bad reaction then apply it to the whole plant. But if the leaf seems burned or curled after applying the homemade fungicides, dilute it with more water. 

4. Root Rot

Root rot is pretty similar to stem rot. Because they also make dark black spots on the stem. In addition, the leaves start to wilt and the whole plant eventually dies. Sometimes when the plant is not getting enough sunlight or they are in damp condition then root rot will easily occur.

It’s very devastating for the ZZ plant. Because in root rot the fungus starts to use the root as their food. And this harms the root functions of water and nutrient movement. As a result, the ZZ plant dies. But you can revive your ZZ plant if you treat them properly without any delay.

Control Measure

In root rot, the soil will smell very bad along with the black spots on the stem. But to be completely sure you have to uproot the plant to examine the roots. The infected roots will be greyish and mushy with a foul smell. 

First of all, you have to repot the ZZ plant in another fresh soil mixture. And before that remove all the infected roots with clean sharp scissors. The next thing you need to do is apply a good fungicide. Follow the label instructions while preparing the fungicide and apply it on the base. 

Just like in stem rot you have to follow the same watering instructions. Also, you need to remove all the diseased plant parts to keep the ZZ plant healthy. Always keep them in a room that has good aeration.

You can also make vinegar fungicide and copper fungicide all by yourself to treat root rot. The recipes are here:

#Recipe 1:- Vinegar Spray Fungicide Recipe

Ingredients:

  • 1 teaspoon of apple cider vinegar 
  • 1  liter of water
  • Few drops of mild liquid dishwashing soap

Steps:

  • Mix the  apple cider vinegar in water very well in a mixing bowl
  • Put the mixture into a sprayer
  • Spray it on your ZZ plant up to  twice a week until the problem is solved

#Recipe 2:- Copper Spray Recipe

Ingredients:

  • 1 liter of water
  • 15 ml of copper sulfate
  • 2 tablespoons of Calcium hydroxide (hydrated lime)

Steps:

  • Add water and hydrated lime in a plastic bowl or bucket. Never use any metal objects because the ingredients in this recipe react with metals
  • Stir the mixture gently with a plastic spoon
  • Keep stirring slowly and add copper sulfate into the mixture. If you don’t keep stirring the mixture will settle down on the bottom of the bowl
  • Now put the mixture into the sprayer and shake it very well before using
  • Spray it on your ZZ plant every week until the root rot problem is solved
  • Don’t keep the leftover mixture for future use
  • Wash the sprayer very well after application. Because this mixture is very corrosive

5. Leaf spot

This is also caused by a fungus that also causes black spots on the stems along with the leaves. As the disease progresses the spots on the stem get bigger. Eventually, the spots merge and end up making the whole stem black.

Control Measure

Apply a good fungicide on the soil to keep these soil-borne diseases at bay. And remove the spotted leaves to reduce the fungal spread. Leaf spots occur mostly when the condition is damp and humid. So, keep your ZZ plants in a well-ventilated room. 

The good news is it’s not as fatal as root and stem rot. You can also follow the same measures of stem and root rot to control this disease.

You can use all the homemade recipes mentioned above to control leaf spots on your ZZ plant.

How To Fix Black Spots On ZZ Plant Stems

You can treat the black spots on your ZZ plant stem if you take a  combined approach from the very beginning.

At first, start with shifting your plant to a shaded but bright-lighted room with nice air circulation. Then water them only after inspecting the soil condition.

It’s better if you water them very little multiple times a week. Remember that they don’t need much water in the winter season so it’s better if you water once every 3 or 4 weeks during that time.

Do not mist your plant very frequently because it will invite fungal problems. Change them into larger pots when the ZZ plant gets bigger. 

Apply fungicides (either store-bought or homemade) at regular intervals to keep your plant protected from other fungal attacks. 

Frequently Asked Question (FAQs)

1. Can a ZZ Plant Get Too Much Sun?

Yes! They don’t even like to be under direct sun. So you always have to keep it under shade.  

2. Can ZZ Plant Recover From Black spots?

If the black spots are on the leaves then after fixing the issue the ZZ plants will produce new healthy leaves.

But if the black spots are on the stem they are more likely to stay as long as the plant lives. But if you treat it properly, new growth in the stem will be spot-free.

3. How to Know if the ZZ plant has Root Rot?

If you uproot the ZZ plant carefully you will see the roots are slimy and mushy with a very foul smell. In addition, the infected parts of the roots will look black or grey.

Conclusion

Black spots on your ZZ plant stem will make an unpleasant appearance in your house. And no plant lover wants to have that. But fixing the spots is a challenge for anyone without having proper knowledge. 

The good news for you is, In this article, I have tried to cover all the areas about the reasons that can cause black spots on your ZZ plant stem. I hope all this information was helpful to you in identifying the causes as well as taking control of the problems. 

If you have any questions or queries please let me know in the comments. I will try to get back to you as soon as possible.

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