ZZ plants are one of the easiest indoor plants to own. However, since they’re tropical plants, you have to ensure you’re providing the right growing conditions.
Having spots on your plant’s stem is a sign there’s a problem with its environment.
If you have this issue, don’t worry. You can still save your ZZ!
Read on to learn why your ZZ plant has black spots on the stem. As a bonus, I’ll also cover the best solutions to each cause.
Let’s get to it!
These factors may cause black spots on your ZZ plant’s stem.
ZZ plants prefer bright, indirect sunlight for just 6 to 12 hours a day. It’s better to keep it indoors beside a south-facing window.
Exposure to too much sunlight can cause sunburn on ZZ plants.
It isn’t a serious issue, but the spots won’t disappear from the stem even if you correct the plant’s position.
Sunburn is a stress response that may appear as dark patches or stripes around a ZZ plant’s stem.
Note that sunburn doesn’t cause moistness or sliminess in the darker areas.
To prevent this issue, you simply have to move the ZZ to a more shaded area. After this, you should observe if your plant looks healthier.
Since the dark patches won’t disappear, you can cut the stems above the roots if you don’t like seeing the spots. However, this isn’t necessary for the plant’s survival, and you may do more harm than good.
These plants have waxy leaves that lock moisture in. What’s more, they have rhizomes that store liquid like potatoes do.
Due to this, you only have to water your plant once every two weeks. Overwatering can cause root and stem rot!
You can tell if your ZZ has stem rot if there are black spots near the base of the plant.
The spots are usually slimy, and you’ll notice the roots rotting if you pull the stems out from the soil.
If you’ve overwatered your ZZ plant, it’s vital that you re-pot it immediately.
Gently brush the soil away and be careful of damaging the roots. Next, place the ZZ in a new pot with fresh soil.
You have to make sure there are proper holes in the pot for drainage. Also, don’t forget to use a sandy type of soil!
Avoid watering the ZZ plant until the potting medium is completely dry.
While many bugs can infest ZZ plants, one pest can appear as dark spots on stems.
Fern scales and brown soft scales may come from nearby greenery. They can appear on the leaves and stems of young plants.
These insects can cause deformation and eventually kill your ZZ!
Scales look like dark circle bumps, about 3/16 inches large, on the stems and leaves of plants. They have a shiny outer shell.
If a scale is hosting a parasite, it can appear dry and black.
Once you spot a scale infestation on your plant, you should isolate it immediately!
You can prune stems with the bugs, and treat the plant with alcohol, neem oil, or horticultural oil. It’s possible to physically remove the scales as well.
For scales with parasites, you can avoid using insecticides since the parasites will help you kill the pests.
Any ZZ with scales can also have sooty mold as a result.
Sooty mold is a black fungus that feeds on the honeydew produced by scales.
This mold appears during warm months on moisture-stressed plants. It doesn’t take nutrients from vegetation, but it can block sunlight if it’s growing on the leaves.
Sooty mold looks like tiny black spots on the surface of the plant. The spots are close enough together that it can appear as if the plant is black.
Some molds cover the leaves, while other types target the stems.
To treat this fungal disease, you can wash any scales and mold off with water. Follow this up by applying horticultural oil or insecticide to the affected areas.
Why does your ZZ plant have black spots on its stem?
The short answer is it may be under too much sunlight. It’s also possible you’re overwatering your plant.
To add, insects like scales and fungi like sooty mold can infect ZZ plants. You can address these issues by changing the environment for your ZZ or by using insecticides and fungicides.
When you treat your plant correctly, you may grow it for years to come!
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.