Black/Brown Spots On My ZZ Plant Stem: Causes+Fix

ZZ plants are hardy and tolerant plants that can survive much neglect and problems. But black or brown spots on the stems of your ZZ plant can kill your ZZ plant if you don’t take action.

Excessive sun exposure, root rot, fungal infections, too much moisture around the ZZ plant, and incorrect soil conditions can cause black or brown spots on the stems of the ZZ plant. To fix the issue, move the plant to a well-ventilated area, limit watering, and trim damaged stems and leaves.

This article will focus on the problems that can lead to brown and black spots on your ZZ plant stems. We will also discuss the treatment and ways to prevent this problem in your ZZ plant.

Black/brown spots on the ZZ plant stem

The black or brown spots on the ZZ stems can be natural if they are part of the stem.

But if you notice a growing spot that is soft and mushy and is gradually growing in size, it is a matter of concern.

Black or brown spots on the stem of the ZZ plant are common and happen for multiple reasons, among which fungal infestation due to too much water is the leading reason.

ZZ plants have rhizomes or bulbs under the soil resembling potatoes, which store the moisture and nutrients for the plants.

Thus the water requirement for these plants is low as they do well in little water.

Also read: How to fix an overwatered indoor plant?

Reasons for the black/brown spots on the ZZ plant stem

ZZ plants have rhizomes underground from which the plants grow.

These rhizomes can store a lot of water inside them.

This is the way these plants native to arid regions grow and adapt to low water availability.

1. Too much water

Thus one of the most common reasons for the death and sickness of these plants is too much water.

They require very less water to survive and are highly prone to overwatering.

We commonly make the mistake of watering our Z too frequently.

Though these look like tropical plants, they are semi-succulents belonging to arid areas.

In most regions, these plants do not need water more than twice a week because the rhizomes store all the excess water and keep them hydrated. 

Also read: How to water a ZZ plant?

2. Poor soil

ZZ plants, being desert plants, require very loose and coarse soil that will not hold any moisture.

In most situations in indoor gardens, these plants grow in heavy clayey soil, making them chunky and tight.

The soil does not let airflow, and the roots suffer from suffocation.

The lack of airflow and the wet cloggy soil contribute to the stem’s developing black and brown spots.

3. Excessive large pot

We often make the mistake of transplanting our plants into a large pot so that we do not need to transplant them again anytime soon.

Though for moisture-loving plants, it is still tolerated for succulents like ZZ, which needs drier soil, this is a big problem that causes many diseases in the plants.

This is because too big a pot holds a lot of soil, which is why it stays wet for longer.

This soil continues to remain wet and does not let air circulation inside. 

This can cause too much moisture around the stem leading to spots. 

4. Plant sitting in water

Another common mistake we make unknowingly is that after watering our plants, we forget to empty the cache trays where all the excess water gets collected.

We leave the pots sitting on the water trays.

For plants that need to stay in dry soil like ZZ, it is mandatory that after watering, you remember to empty the trays.

Keeping the pots in the trays makes the plant’s roots remain wet as the soil keeps soakings up all the water from the cache.

This leads to overwatering and diseases in the roots causing spots on the ZZ.

5. Too much light exposure

ZZ plants can also develop spots from exposure to too strong light.

As we know, ZZ plants do not like harsh direct sunlight.

Thus, exposing the plant to prolonged hours of scorching sunlight might show signs of stress by developing spots on them.

6. Poor ventilation

Poor ventilation, especially for indoor plants, is a problem many plants suffer from.

Often, plants are kept cramped in corners where airflow and light cannot pass freely around one another.

It happens due to our homes’ lack of space, air, and light.

But due to insufficient ventilation, a lot of problems are caused.

Lack of airflow causes pests and fungus growth in the plant.

It also increases the risk of overwatering and root rot as the soil’s excess water does not evaporate quickly and stays wet for a long time. 

7. Root rot

Root rot is a disease caused by overwatering.

When the plant stays in wet soil without airflow, the fungus attacks the plant’s roots.

The healthy root gradually begins to rot and, if not cured, eventually dies. 

8. Fungal infection 

One cause for black and brown spots on the stem could be fungal infestations such as black fungus.

Bacteria and pathogens cause these.

When the ZZ receives too much water and moisture, the conditions become a breeding ground for this fungus.

This fungus attacks the plant and causes spots, weakening it by sucking out its nutrients.

They travel to the stem from the soil and quickly target the entire plant.

As it spreads, it covers the plant’s body in black spots and patches, which weakens the plant gradually, and if this condition is not corrected, it can get difficult to cure the situation.

9. Excess moisture around the plant 

Plants like ZZ need dryness around them.

Misting cannot be very effective.

Misting can give too much humidity around the plant, which ZZ plants o not like.

Too much moisture leads to a damp and humid condition that becomes an ideal spot for fungus to cause spots on the plant.

How to fix back spots on the ZZ plant stem?

ZZ plant is meant to survive difficult conditions as a forgiving and easy plant.

So even if you suspect the plant is suffering from the above problems, you can correct the situation easily and treat the problem.

Here are the best ways to fix the nasty spots:

1. Leave the plant alone

If the fungus problem is at an initial stage, you can cure it quickly by keeping the plant dry and not disturbing it much.

The moment you notice the spots growing on the plant, immediately cut down on watering and moisture from around the ZZ plant, as the most common cause of this problem is overwatering.

If the pot is on a tray filled with water, empty it immediately.

If the soil stays wet for a long time, change the plant’s location and move it to a more ventilated spot.

2. Repot the plant

If the problem is not curing, and the infection has gotten more severe, the best you can do is repot the plant as soon as possible.

To repot the ZZ plant, do the following:

• Prepare a fresh soil mix. Make the soil light and loose. An ideal mix for your ZZ plant would be 1 part soil, 1 part sand, 1 part perlite, and 1 part compost. These ingredients together would take care of the drainage and keep the soil airy.
• Take the ZZ out of the pot and wash the root ball under running water.
• Examine the roots carefully to identify any signs of rotting.
• Trim any infected parts of the roots with a sterilized pruner.
• Now replant the ZZ in the fresh soil in a new pot.
• Water the plant thoroughly and then let it adjust itself to its new home.

3. Limit watering 

Cut down on watering when you notice such spots on your ZZ plant.

Make sure the soil goes dry between watering.

If you are unsure when to water your ZZ plant, use a moisture meter or do a finger test to check the soil’s moisture before watering.

Do not water until you see the soil is totally dry.

Remember to keep watering is better than shallow watering.

Water the plant once or twice a week, depending on the temperature of your region.

4. Trim the damaged stems

Cut all the infected leaves or branches you find on your ZZ plant.

However, remember not to trim more than 25% of the plant at a time.

5. Change the spot

Move the plant to where it gets bright indirect light and a few hours of morning sunlight.

Keep it shaded from scorching afternoon sunlight, which can burn the plant.

Even though ZZ thrives in the shade, a few hours of early morning sunlight in winter can give the plant some warmth.

6. Keep the soil dry 

ZZ plants prefer soil on the drier side.

Keeping it dry can reduce the chances of pests and fungus breeding in the soil. 

7. Spray fungicide

If you see the spots have reached an advanced stage and are refusing to leave the plant, you need to use a fungicide without further delay.

There are many available fungicides in the market that help treat this infection.

If you do not want to use chemical fungicides, you can use Neem oil judiciously, which is the most effective organic fungicide.

However, remember you must spread it 3-4 times weekly to treat it fully. 

And once it is cured, you can still spray it once in 1-15 days as a preventive measure.

8. Do not mist 

Misting is one of the rare routines most plant lovers do generously daily.

However, for certain succulent and desert plants like ZZ, it is not recommended to mist the plant.

They do not like too much moisture and prefer drier air around them. 

Misting increases the humidity around the ZZ plant, which can aggravate the development of these nasty spots on them. 

9. Keep the plant in a well-ventilated spot. 

Always keep the plant in a spot with good ventilation and airflow.

Increasing airflow around plants helps immensely to cure infections and keep them fresh.

10. Always use clean and sanitized tools.

Remember, infected tools can spread fungi and pests from one plant to another.

So never use tools without sanitizing and washing them the first ad sanitize them after using the too, as this will kill any fungus that might have gotten on them.

Prevention tips to keep your ZZ healthy

To prevent the reappearance of the nasty black spots on the plant, you need to follow the below tips to give the correct environment to your ZZ plant.

• Avoid exposing your ZZ plant to too long hours of scorching sunlight.
• Always sterilize the tools and equipment before and after usage to prevent the spread of pests or fungi.
• Keep the ZZ at a spot that receives a lot of good airflow and light. The plant should not be kept suffocated in a corner.
• Do not keep the environment around your ZZ plant damp and excessively high in humidity. Make sure it stays dry to limit the chances of fungi attack. 
• Fertilize the ZZ plant during the growing season as they are not too heavy a feeder. Do not feed them during winter. Feeding them too frequently or in more quantity can harm the plant by burning its rhizomes. 
• Water only when the soil is dry. Remember, the root system of ZZ plants store water in their rhizomes, so even when the soil looks dry, the plant still has water in them. So wait for a few days before watering the ZZ plant again. 
• Do not use an extremely big pot to grow your ZZ plant. Remember, a big pot would unnecessarily hold too much water, thus making the ZZ plant prone to diseases. 
• Never forget to empty the cache or trays under the pot after watering. 
• For plants like ZZ plants that do not like much moisture, it is recommended to grow them in clay pots as they are porous and breathable and the soil does not stay clogged with water for to soil. 
• Ensure to use the correct mixture of potting soil for the ZZ plant. Keep the soil very light and porous so it does not remain clumpy. 

Final thoughts

ZZ plants are the easiest plants to grow, but that does not mean your plant will flourish in unsuitable hard conditions. Ensure you provide your plant with the ideal growing condition for it to flourish.

If the ZZ plant shows signs of black or brown spots on the stems, look for the above-explained problems and take the necessary actions. They are hardy plants and can survive most conditions.

If you take the correct treatment, your ZZ will survive. First, you need to identify the cause behind the brown ad black spots and correct it by taking the necessary measures.

Also read: How To Care For ZZ Plant?

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Sources: ZZ plant study, College of agricultural studies, University of Vermont, National science foundation.