ZZ Plant Root Rot: Causes, Important Detection Tips & Solutions

ZZ plants don’t require much care and attention, but you must avoid common mistakes. The commonest mistake of all is overwatering. ZZ plants come from east Africa, where they grow in shaded areas and can survive long dry periods followed by torrential rains that quickly drain away.

ZZ plant root rot usually results from overwatering and happens below the surface where you can’t see it. It can be deadly, so you have to act fast if you suspect it. You must trim off all the brown dead roots and stems and repot the plant in fresh well-draining soil. Even this may not save it.

The plant is adapted to store water in its roots, leaves, and rhizomes for considerable periods to last through the lean season when there isn’t much rainfall. When kept as an indoor plant, it is not subject to the vagaries of the weather, but its unique adaptations remain.

Also Check: ZZ Plant Overwatering: 4 Signs & Effective Solutions

What Causes Root Rot?

Root rot is caused by too little oxygen and too much water within the soil around the plant’s root system. Too much water impedes the flow of oxygen and nutrients into the roots and will eventually kill the plant. If the soil is constantly waterlogged, this also encourages fungi and other organisms that can destroy the roots.

Fungi in the soil around the plant are usually unavoidable, but they lie dormant in dry aerated conditions. When there is excess moisture, they start to grow and multiply, which is bad news for your ZZ plant!

Since water displaces the air around the roots of your ZZ plant, healthy aerobic bacteria die off because they need oxygen to live. Unhealthy anaerobic bacteria take over because they don’t need oxygen, and they can cause the roots to rot.

ZZ plants need a well-draining, aerated substrate that allows water to drain away instead of accumulating around the roots. If you have repotted your ZZ plant since you bought it and have used only potting soil as the new substrate, it could be too dense.

 Root rot can set in not necessarily because you have been watering too often but because the substrate never dries out enough between waterings.

Fusarium is a fungus commonly found in soil that can cause root rot. It overruns dead or dying plant material, and overwatering causes its growth to explode. Pythium is a parasitic bacterium that feeds on decaying plant material. Fungus gnats transmit it on their feet as they move between plants.

ZZ Plant Root Rot

A pot with inadequate drainage holes traps too much water around the root system.

Terracotta pots are usually preferable to plastic and ceramic pots because they are porous and wick excess water away from the soil, allowing it to evaporate from the pot’s surface. You should always empty the drip tray if you see water in it.

Good air circulation also goes a long way to keeping your ZZ plant healthy. If the air is stagnant, it cannot carry water vapor away from the soil, and the pot can be constantly soggy. Grouping plants together raises humidity levels amongst them which can be a good thing, but it can also cause poor ventilation.

To avoid transmitting fungal and bacterial infections to your plants, you should always sterilize the tools you use for indoor gardening after every use.

How To Detect Root Rot

Root rot is not evident from just looking at the leaves and stems of the plant. It is insidious as it happens underground where you can’t see it. The first signs you may get that root rot has taken hold will be the wilting and yellowing of your ZZ plant’s leaves.

However, yellowed leaves may also be due to underwatering, too much light or fertilizer, or extremes in temperature. ZZ plants prefer moderate temperatures, relatively dry conditions, and indirect light. Swamps do not feature in their natural habitat.

The amount of water your ZZ plant needs depends on ambient temperatures, humidity, ventilation, pot size, and light intensity. In arid climates, they will require slightly more water than humid ones. Warmer temperatures and brighter light may also mean more water is necessary.

Since the soil should be allowed to dry out between waterings, the best way to check if your ZZ plant needs water is to use a soil moisture meter. This is an inexpensive device available from many gardening and hardware stores with a simple scale that tells you if the soil is very dry, moist, wet, or very wet. It has a probe that you slide into the soil and does not require batteries.

Leaves that are wilting despite the correct amount of watering can also indicate something is wrong with the plant’s root system. It is a sign of leaf dehydration which sounds crazy because how can the plant be dehydrated if it gets enough water? The truth is that the plant can only absorb water through its roots, and they cannot channel the water to the leaves and stems if they are dying.

As a rough guide, many ZZ plant owners say they water once a week in summer and every three weeks in winter. However, the best way to know whether a ZZ plant needs water is to check the soil. If you don’t have a moisture meter, you can use a clean, dry, unpainted chopstick.

Insert the chopstick to the full depth of the substrate and see if it comes out clean or covered in dirt. If it comes out clean, the potting mix is dry, and you can water your ZZ plant. If it comes out covered in mud, it is wet, and you shouldn’t add any water.

You should drench the substrate when you water a ZZ plant until you see the water draining out of the pot into the drip tray. Adding drops of water here and there is not the proper way to water a ZZ plant. Always empty the drip tray, so the plant is not standing in water.

Checking For Root Rot

Checking root rot

Now that you have the above information, you’re in a better position to assess whether your ZZ plant’s leaves are yellowing due to overwatering or some other cause. If you have been overwatering, the only way to check for root rot is to remove the plant and examine the root system.

Since the sap of the ZZ plant contains an irritant called calcium oxalate that can cause a skin rash in some people, it is a good idea to pull on a pair of rubber gloves before taking your ZZ plant out of the pot in case you accidentally break a few leaves or a stem.

To do this, hold one hand below the pot and slowly turn it upside down. Slide the plant together with its substrate cautiously out of the pot. Do not attempt to pull it out by the stems because they will break off. If it’s stuck inside the pot, run a blunt knife or similar tool between the rim and the soil to loosen it.

Once the ZZ plant is free, gently remove the substrate from between the roots with your fingers until you can clearly see its root system.

Notice the consistency of the substrate as you do. If it is relatively dry and crumbles away quickly, your plant is probably not suffering from root rot. If it is soggy and sticking to the roots, this may be a bad sign. You should see small swollen bulbs amongst the roots, which are the rhizomes in which the plant stores water.

Healthy roots and rhizomes are a pale grayish white and firm to the touch.

Dealing With Root Rot

If the roots and rhizomes are brown or black, your plant has root rot. Rinse away all soil particles around the roots using room temperature water. Then trim away all the mushy, dead tissue using clean, sharp scissors or shears.

You can try applying a fungicide to the remaining roots by dipping them in the solution. Using a fungicide is not without risk, as it can cause further damage. No one chemical kills every type of fungus, and if bacteria have caused the root rot, a fungicide won’t help.

Cinnamon powder is a natural fungicide that can be dusted onto the healthy roots of your ZZ plant once you have cut off all of the diseased parts.

Another potential remedy is hydrogen peroxide. It’s sold in different concentrations, but you should only use the three percent one. Mix one or two teaspoons of hydrogen peroxide in a liter of water and stand the roots in it for an hour before repotting.

Use a new pot or wash the old one in a weak bleach solution before repotting.

Read more: ZZ Plant Repotting: Detailed Guide (Plus 6 Important Repotting Steps)

Conclusion on ZZ Plant Root Rot

Root rot can be devastating to a ZZ plant, and if you’re an inattentive owner, you may not realize there’s trouble afoot until it’s too late. Examining the root system is the only way to establish the presence of root rot. Prune away dead roots, leaves, and stems and repot the plant in a fresh, aerated, well-draining substrate as soon as possible.

References & Other Resources:

https://www.ukhouseplants.com/plants/zanzibar-gem-zz-plants

https://smartgardenguide.com/zz-plant-yellow-leaves/

https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm

https://smartgardenguide.com/root-rot/