Why Your ZZ Plant Stems Are Turning Yellow

Why Your ZZ Plant Stems Are Turning Yellow

I have three ZZ plants in my apartment, and I almost killed the first one within six months of bringing it home. The stems started turning yellow from the base, and I panicked because everything I read online said ZZ plants were “impossible to kill.” Turns out, that is exactly the problem. When people tell you a plant is indestructible, you tend to treat it like it doesn’t need anything at all, or worse, you overcompensate.

If your ZZ plant stems are turning yellow right now, I want you to take a breath. This is fixable most of the time, but you need to act fast and you need to understand what is actually going wrong. I am going to walk you through exactly what I learned the hard way, plus what the research actually says about saving these plants.

The number one killer: Overwatering

Let me be blunt. If your ZZ plant has yellow stems, you probably watered it too much. I know that sounds harsh, but according to horticulture extensions at multiple universities, overwatering accounts for about 90% of ZZ plant problems (University of Florida IFAS Extension). These plants evolved in East Africa where they go weeks without rain. Their thick rhizomes (those potato-like structures under the soil) store water like crazy. When you add more water before the soil dries out, those rhizomes start to rot.

Here is what happened with my first ZZ. I watered it every week because that is what I did with my pothos. Big mistake. ZZ plants need water maybe once every two to three weeks in the growing season, and even less in winter. The soil needs to dry out almost completely between waterings.

When you overwater, the roots cannot breathe. They sit in soggy soil, and root rot sets in. Once the roots start rotting, the rhizomes follow. Then the stems turn yellow because they are not getting nutrients anymore. The whole system is breaking down from the bottom up.

You can test if this is your problem right now. Stick your finger into the soil, all the way down to your second knuckle. If it feels even slightly damp, do not water. If the pot feels heavy when you lift it, do not water. I learned to pick up my pots before watering, and it changed everything. A ZZ plant that needs water feels light, almost hollow.

The other thing I did wrong was using a pot without drainage. I thought the decorative ceramic pot looked better than a plastic nursery pot, so I planted directly into it. Never again. Without drainage holes, water has nowhere to go. It just sits at the bottom, rotting the roots. Even if you are careful about watering, you need drainage. Always.

Checking the rhizomes for mushy rot

Once I figured out I had been overwatering, I needed to know how bad the damage was. That meant checking the rhizomes, which honestly felt intimidating the first time. But if you want to save your plant, you have to look.

Take the plant out of its pot. I usually do this in the bathtub or outside because it gets messy. Gently shake off as much soil as you can. You will see those thick, potato-like rhizomes at the base of the stems. Healthy rhizomes are firm and solid when you press on them, kind of like a raw potato. They are usually light tan or cream colored.

Rotten rhizomes feel mushy. When you press them, they give way like a sponge. Sometimes they are darker, almost black or very dark brown. If you see any rhizomes that look or feel like this, you need to remove them. I use clean scissors or pruning shears that I wipe down with rubbing alcohol first.

Cut away any mushy rhizomes and any stems attached to them. This is hard because it feels like you are making the problem worse, but you are not. Rotted tissue spreads. If you leave it, the rot will keep traveling to healthy parts of the plant. According to research from Iowa State University Extension, removing all diseased tissue is critical for saving plants with root rot.

After I cut away the bad parts on my ZZ, I let the remaining healthy rhizomes air dry for a few hours. Some people say to let them dry overnight, and if you have time, that is probably better. The cut surfaces need to callous over slightly so they do not absorb too much water when you repot.

One thing that surprised me was how much of the plant I had to remove. My first ZZ lost about half its stems. It looked pathetic for months, but it did eventually grow back. ZZ plants are slow growers, but they are tough if you give them the right conditions.

Above: A close up look at the symptoms.

Why the stalks are wrinkling

Sometimes the stems are not just yellow, they are also wrinkling or shriveling. This threw me off because I thought wrinkling meant the plant needed more water. Nope. In a ZZ plant, wrinkled stems usually still point back to a watering problem, but it is more complicated than just “add water.”

If you have been overwatering and the roots are damaged, the stems cannot pull up water even if the soil is wet. So they start to wrinkle because they are dehydrated, but the actual problem is root rot from too much water. I know that sounds backwards, but it is a common situation. Your plant is basically drowning and dying of thirst at the same time.

The other cause of wrinkling is actual underwatering, but this is way less common. If you have ignored your ZZ for two months and the soil is bone dry, then yes, the stems might wrinkle from lack of water. But most people do not underwater ZZ plants. We kill them with kindness.

Here is how to tell the difference. Check the rhizomes like I explained above. If they are mushy, your problem is overwatering even if the stems look dehydrated. If the rhizomes are firm and the soil is completely dry, you might actually need to water.

When I had the wrinkling problem, I checked the rhizomes and found rot, so I knew watering more would just make things worse. I had to cut away the bad parts and start over with better watering habits.

One more thing about wrinkled stems. Sometimes just one or two stems wrinkle while the others look fine. This can mean those specific stems are attached to a rhizome that is dying while the rest of the plant is okay. You can cut off the affected stems at the soil line and let the rest of the plant keep going.

Repotting a sick ZZ plant

After you have trimmed away the rotten parts and let the rhizomes dry, you need to repot into fresh soil. Do not reuse the old soil. It probably has fungal spores or bacteria from the rot, and you will just restart the problem.

I use a succulent or cactus potting mix for my ZZ plants now. Regular potting soil holds too much moisture. You want something that drains fast. If you only have regular potting mix, you can add perlite or coarse sand to improve drainage. I do about one part perlite to two parts potting soil.

Choose a pot that is just slightly bigger than the root ball, and make sure it has drainage holes. I cannot stress the drainage thing enough. After my first disaster, all my plants go in plastic nursery pots with drainage, and then I put those inside decorative pots if I want them to look nice. That way I can take the plant out, water it in the sink, let it drain completely, and then put it back.

When you are repotting, do not bury the rhizomes too deep. They should sit just below the soil surface or even slightly exposed. I made the mistake of planting mine too deep the first time, which kept the rhizomes too wet.

After repotting, do not water right away. I know this feels wrong, but the rhizomes need time to settle and start healing. Wait at least a week before you water. The first time I did this, I was so nervous the plant would die from dryness, but it was fine. Remember, these plants store water in their rhizomes. They can handle a dry period way better than a wet one.

Put your repotted ZZ somewhere with bright, indirect light. Not direct sun, which can stress it further, but also not a dark corner. I put mine about six feet from an east-facing window, and it did well there.

Above: The tools you need to fix this.

Can you save a yellow stalk?

This is the question I get asked most by friends who see my ZZ plants: if a stalk turns yellow, will it turn green again? The short answer is no. Once a ZZ stem goes yellow, it stays yellow and eventually dies. You cannot reverse it.

But here is the important part. A yellow stalk does not mean the whole plant is doomed. If the rhizome attached to that stalk is still firm and healthy, the plant can grow new stems. You just have to cut off the yellow one.

I cut yellow stalks at the base, right where they emerge from the soil. Use clean scissors or shears. Some people leave the yellow stalks until they fall off on their own, and that is fine too, but I think it looks better to remove them and it prevents any potential rot from spreading.

The hard part is waiting for new growth. ZZ plants are painfully slow. After I saved my first one, it took about four months before I saw a new stem poking up. I honestly thought it was dead and I was just keeping a pot of dirt around. But eventually, a little green shoot appeared, and over the next year, the plant filled back in.

If most or all of your stems are yellow and the rhizomes are mushy, you might not be able to save the plant. I hate saying that, but sometimes the rot is too far gone. You can try cutting away everything that is damaged, but if there is nothing firm left, the plant will not recover.

One technique I learned from a University of Minnesota Extension publication is to propagate healthy stems before the whole plant dies. If you have even one green, healthy stem, you can cut it off with a bit of rhizome attached and pot it separately. It is like taking a cutting. This gives you a backup in case the main plant does not make it.

I have not had to do this myself yet, but a friend did it successfully with her ZZ after a bad case of rot. She ended up with three smaller plants from the divisions, and they all survived.

The key takeaway is that yellow stems are a symptom, not the disease itself. Fix the underlying problem, which is almost always too much water, and your plant has a good chance of bouncing back. It will not be quick, and it will not be pretty for a while, but ZZ plants are surprisingly resilient once you figure out what they actually need.

I water mine about once every three weeks now, sometimes less in winter. I check the soil and the weight of the pot every time. I have not had a yellow stem in over a year. You will get there too.

References

Iowa State University Extension and Outreach. “Root and Crown Rots.” Horticulture and Home Pest News.

University of Florida IFAS Extension. “Zamioculcas zamiifolia: ZZ Plant.” Environmental Horticulture Department.

University of Minnesota Extension. “Houseplant Diseases.” Department of Plant Pathology.