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7 ZZ Plant Diseases and Issues You Should Know About

7 ZZ Plant Diseases and Issues You Should Know About

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Do you struggle to get your ZZ plant to look as gorgeous as they do in other people’s photos or homes? It’s much easier to get the healthy dark foliage on the ZZ plant when you know how to address and fix any of the diseases and issues they can succumb to.

Diseases and Issues to Look for on Your ZZ Plant

1 – Rhizomes Above the Soil

Some people refer (incorrectly) to the root bulb of a ZZ plant becoming exposed above the soil line. The ZZ plant doesn’t have a root bulb, nor is it a tuber.

It grows from rhizomes, which are best cared for by keeping them buried at least an inch beneath the soil surface. They do grow horizontally so they won’t grow out of the soil naturally. The problem is rather that the top soil is being depleted, and that’s usually caused by overwatering, or watering from above.

When the rhizomes become exposed above the soil line, it leaves them open to decay, susceptible to insect damage, and they may rot if the conditions aren’t adequate.

It’s the role of the rhizomes to store the food, nutrients and moisture that the ZZ plant needs to thrive. When they become exposed, it puts the entire plant at risk.

The best course of action to take with exposed rhizomes is to either to top up the soil to keep them buried, or repot the plant in a suitably sized container. One that gives it sufficient depth to keep all the roots/rhizomes buried to a depth of at least an inch.

As the rhizomes grow horizontally, you can use a shallow pot, however, the smaller the pot, the sooner it’ll need to be repotted.

Generally, ZZ plants need to be repotted every other year. As your plant grows, so do the rhizomes. When those become exposed, it can be a sign that it needs a bigger pot. To know if it does, remove the plant from its current container and inspect the conditions beneath the soil.

ZZ plants like room to spread their rhizomes so preferable is to have them at least an inch away from the wall of the pot. If they are crammed against the edge of the pot, it will be too crowded for growth.

When repotting, go with a pot size that is two inches bigger than its current pot to ensure there’s sufficient room for growth.

2 – Hemiptera Insects

The ZZ plant can succumb to numerous plant pests, the majority of which are classified as true bugs: Hemiptera insects. These have modified mouthparts that they use to pierce plant leaves to feed on the sap within them.

The main hemipteran insects attracted to the ZZ plant are spider mites, mealybugs, scale insects, aphids, and fungus gnats.

Each have mouthparts that can pierce through the leaves of plants, which then enables them to feed on the sap within the leaves. Additionally, they are fast breeders and can lay eggs in the soil. If a pest problem is not addressed, an infestation is likely.

Spotting the pests early on is tricky because of their tiny size. It’s more likely you’ll notice the damage they do first, even in small numbers.

  • Mealybugs look like a tiny ball of cotton. These tend to congregate on new growth and near leaf axils.
  • Spider mites are only about 1mm in size making spotting those difficult. Symptoms of these being present on plants is webbing on the leaf surface.
  • Aphids can be green, black, brown, yellow or gray, and like spider mites, these are all miniscule in size. They are soft-bodied creatures with a pear-like shape and tend to congregate on new growth and hide in crevices. Mostly on the underside of the leaf surface. Whitefly is similar in appearance to aphids and will cause the same damage in sufficient numbers.
  • Scale insects tend to be brown or black and look like tiny brown bumps on plant leaves. These can be picked off.

The direct damage pests do is create holes in the leaves of the ZZ plant, raising the potential risk of disease infecting the plant. Secondary damage is the plant’s distortion from stunted growth, leaf wilting, curling and foliage discoloration. Usually, leaves turn yellow first before they turn brown, then drop eventually.

In small numbers, these pests can be picked off. Larger populations can be treated with either insecticidal soap or neem oil. Both are effective at getting rid of bugs on houseplants safely.

3 – Black Spots on the Leaves of ZZ Plants

Black spots on leaves are an indicator of a fungal or bacterial infection in the soil. It infects the root structure and the damage is seen up top on the leaf surface.

The spots start out as a small yellow blotch either on the leaf surface, the leaf edge, or right on the tips of the leaves. Before long, the yellow spot turns to a black spot with a yellow halo ring around it.

Once this appears, the leaves are beyond recovery. The best course of action is to snip away all the damaged leaves and repot the plant in a fresh potting mix.

The overarching problem that results in black spots is the roots being exposed to excessive moisture, or a lack of air circulation, such as when the plants leaves are overcrowded.

4 – Curling Leaves

Leaves curling on the ZZ plant is a defense mechanism to conserve moisture. The puzzle for you is to identify what the plant is defending itself against. It can be a few things.

Common causes of leaf curl are direct sunlight, dehydration, or exposure to cold drafts. If the plant hasn’t been repotted in a while, the rhizomes being pot bound may be causing a lack of nutrition that leads to leaf curl.

Maintaining adequate moisture levels in the soil, ensuring sufficient humidity levels (40% to 50%), and exposing the plant to at least a few hours of bright, indirect sunlight keep the foliage of the ZZ plant healthy.

Over or underdo it with the watering, light exposure, or humidity, the leaves can begin to curl in on themselves. Correct the growing conditions and the leaves will unfurl.

5 – Pale Green Leaves

New growth is pale green. They darken as they mature. Or they should anyway.

When mature leaves turn pale green, it can be the start of the leaves yellowing. That is an indicator that the plant has been overwatered.

The science behind the paler foliage is this…

The dark green foliage on ZZ plants is because of nitrogen. Without it, the plant can’t develop chlorophyll, and without that, photosynthesis stalls.

Pale green leaves are indicative of a nitrogen deficiency. Only when the mature dark green leaves turn pale green though. New leaves will always be light green. The plant is smart and will distribute more nitrogen to new growth.

The solution is using a fertilizer. The ideal fertilizer for the ZZ plant is a balanced liquid solution with an NPK of 10-10-10 or 20-20-20.

It needs to be diluted to half strength and is best applied once to twice monthly during the spring and summer, then cutting back in the fall through winter while the plant is dormant.

When feeding with a liquid fertilizer, moisten the soil first, then add the diluted fertilizer. Adding fertilizer to dry soil is less effective and can damage the delicate root structure of the ZZ plant.

6 – Yellow Leaves

Yellow leaves on a ZZ plant are a symptom of too much water in the soil. The root structure is delicate and prone to root rot when it’s left in standing water.

What you need to do is first, cut back on watering. Placed in ideal conditions, you should only need to water a ZZ plant every two to three weeks. It’s best to let the soil dry out before watering again. The brighter the light the plant receives, the more water it’ll drink. In low light conditions, water less.

The ZZ plant is drought tolerant, so you can exercise extreme caution with the amount of water you give it.

Signs of dehydration are the ZZ plant drooping, leaves wilting, and even the stems wrinkling. When you see that, poke your finger into the soil mix and you’ll likely feel the top soil is dry to at least a couple of inches.

Since the ZZ plant is shallow rooted, it’s the top soil that needs to be kept moist and never drenched for too long.

7 – Stunted Growth

The ZZ plant is a slow grower, but it should always be growing during its active season – April to September. When your ZZ plant’s not growing in its active season, that’s an issue!

The growth rate of the ZZ plant tends to be 6 to 12 inches in a month, but that is assuming all conditions are met, including fertilizing.

The cold can stunt the plant’s growth. That can be from a cold draft near a door that is frequently used, an open window, vent, or misting the plant with cold water. When misting to raise humidity, use lukewarm water.

Any sudden changes to the plant’s growing climate can stress it. Stress will stunt its growth. At least until its acclimated to its new spot, which is best to be somewhere with plenty of bright, indirect sunlight.

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