The Most Dangerous Houseplant Diseases You Need to Know About

If you want to create a veritable garden of Eden in your home, you’ll want to know when your houseplants need a little helping hand. Along with understanding their requirements for water, nutrients, and light, you need to look for signs of distress. Pests and houseplant diseases can turn your lush indoor garden into a desert.

Overwatering is the primary cause of houseplant diseases. Overwatering and humid conditions create a suitable environment for the spread of diseases.

Even though we coddle our plants, they’re not completely immune to pest infections and houseplant diseases. To keep your foliage bright, beautiful, and lush, look out for the following signs and symptoms. Then, read up on what you can do to prevent and treat them.

Three Common Causes of Houseplant Diseases

There are three main causes for houseplant diseases: bacterial, viral, and fungal. Like other living things, plants can become infected by organisms that take advantage of a weakened immune system. If left unchecked, they can leave you with barren pots.

Each of these types of disease have separate symptoms and treatments. But interestingly, they all also have a similar causal factor: excess moisture.

Bacterial Houseplant Diseases

Bacterial infections will first show up as dark spots on the leaves of your plants. They may be black or brown, and they’ll destroy the structures of the foliage.

You may find some of these spots around the edges of the leaves, which is often where the bacterium enter the plant.

In some cases, you’ll find the spots growing between the veins of the leaves.

Bacterial infection on a plant

One of the signature marks of bacterial diseases is that the center of the spots will become mushy, wet, and collapse, leaving blistered holes in the plants.

Treatment

For those only mildly affected by this houseplant disease, remove the damaged foliage immediately and discard of it. Make sure you wash your hands and any tools you’ve used on the plant afterward before touching another plant.

Reduce water and stop misting it completely. Isolate the plant from others to prevent the spread of disease until you’re sure it has recovered.

Increase air circulation by adding a fan if possible.

Unfortunately, there is no cure for bacterial diseases in plants once they become systemic. Discard these plants to prevent spreading the infection, including the potting medium. You can sanitize the container by washing it thoroughly with hot, soapy water, and rinsing it with a hydrogen peroxide solution.

Prevention

You can prevent bacterial infection of your houseplants by ensuring that you only purchase healthy specimens. Keep new plants in quarantine after purchasing until you’re sure they’re not harboring any diseases.

Woman's hand touching plants lovingly

Space your plants out to provide adequate air flow between leaves.

Always water at the base of your plants to prevent moisture accumulating on the leaves. Also, water gently to prevent splash-back, where the flow of water causes the dirt to spray up and stick to the foliage. This can transmit soil bacteria to upper parts of your houseplants.

You can also cover the tops of your containers with a sterilized mulching material. This provides a buffer between bacteria in the soil and the leaves of your plants. It can also help reduce splash-back.

Fungal Houseplant Diseases

Fungal diseases often pop up in damp conditions with little airflow. While some plants really love humid environments, others are prone to fungal infections that will mar the appearance of your plant. If untreated, it can also cause your plants to drop leaves, develop slowly, or even die off completely.

Fungal Leaf Spot

Some of the telltale signs of a fungal disease are circular beige or brown spots that dot the leaves and run together. These spots will grow and spread, infecting the stems and roots of your houseplants.

Fungal leaf spot

Treatment

Remove and destroy any spotted leaves, making sure you wash your hands and any tools used thoroughly before tending any of your other plants.

Ensure that the leaves remain completely dry and refrain from misting. If the plant is in a humid location, like a laundry room, outdoor patio, or bathroom, move it to a place with drier air until it recovers.

If badly infected, you can use a commercial fungicide. You can find organic options that are safe for indoor use, including those using a copper or sulfur solution or a naturally occurring bacterial fungicide called Bacillus amyloliquefaciens (strain D747).

A mixture of two tablespoons of Neem oil to one gallon of water may prove helpful. Spray the plant thoroughly with this solution every three to five days until it recovers.

Some plant lovers use a DIY solution of baking soda and water at a ratio of 1 tablespoon to a gallon of water.

If you’re concerned about this houseplant disease spreading to your other plants, you can also mist them all with either solution as a preventative measure on a weekly or biweekly basis.

Root Rot

Root rot is a direct result of overwatering and poor drainage. It’s a fungal infection of the roots and crown of the plant. The plant will appear to be falling apart at the main stem, which is rendered soft and mushy.

Orchid with root rot

Treatment

For root rot, you can make a noble attempt to salvage a sick plant by gently pulling it from its container and removing all potting soil from the roots. Remove any mushy or damaged roots, stems, or leaves. Rinse the roots with a mild solution of six tablespoons hydrogen peroxide to a gallon of water.

Then, repot your plant in fresh, sterilized potting soil in a newly cleaned container. Avoid watering any more than absolutely necessary. Your plant may revive with careful treatment.

Powdery Mildew

While powdery mildew isn’t an immediate death sentence when it comes to houseplant diseases, it can weaken your plant. You’ll first notice it as a grayish, powdery tinge on the tops of the leaves.

Powdery mildew on begonia

This mildew will eventually spread to the bottom of the leaves and onto the stems, seriously damaging the leaves and stunting plant growth.

Treatment

Powdery mildew is one of the easiest of the houseplant diseases to treat. Mist any affected and nearby plants with a mixture of six tablespoons of hydrogen peroxide and one gallon of water.

Thoroughly mist all surfaces of the plant and repeat again after three days, ensuring the plant dries out completely between sprayings. To prevent recurrence, you can also mist lightly with this solution every week or every two weeks.

Botrytis Gray Mold

This fungal disease appears as a gray fuzz on your plant, and can affect the stems, roots, and leaves. It’s commonly found on flowering houseplants like cyclamen, begonias, and African violets.

Botrytis gray mold

Treatment

Remove all diseased parts of the plant as they appear and dispose of them. Move the infected plant to a drier location to reduce humidity, which allows the fungus to grow.

You can also improve the air circulation around your plant with a fan. This disease spreads by air, however, so make sure you isolate any sick specimens from your healthy plants to prevent spreading.

Rust

Rust is a fungal infection that takes its toll on many plants, and if left untreated, can reduce a formerly healthy plant to sad, leafless twigs.

You’ll notice it first as orangey-yellow spots on the underside of leaves, which will then grow into lumps and bumps on the leaves and stems.

Treatment

As with all fungal plant infections, removing excess humidity around the plant is crucial. You can move it to a drier room or provide a ventilation fan.

Geranium rust abaxial side

Remove any leaves marked with rust and destroy them. Commercial fungicides are highly effective on rust, especially solutions made with copper.

Follow the manufacturer’s directions but expect to spray your plant every five to seven days until the disease is eradicated. You can also spray every week afterward for prevention.

Make sure you wash your hands and any tools after working with any plants with a rust infection. This will help keep it from spreading to other plants.

Prevention of Fungal Houseplant Diseases

To reduce the chance of fungal infections in your houseplants, make sure you introduce new plants into your home carefully. Many fungal houseplant diseases ride in on new plants from outdoors or from the nursery.

Use a quarantine system, keeping new plants isolated from others for a week or two before finding them a permanent location.

Good airflow is critical to preventing fungal infections in houseplants. Ensure that your plants are widely placed to allow airflow through the leaves.

To prevent root rot, use a sterile potting medium when repotting your plants. You can purchase new potting soil or sterilize and reuse older soil in the oven or microwave.

Refrain from overwatering your plants and make sure the drainage holes in the container are not blocked.

Viral Plant Diseases

Viral infections can prove to be the most disconcerting houseplant diseases of all. It’s not bad enough that they kill your plants, they can also distort their beauty first.

Jasmine mosaic virus

Signs of viral infections in houseplants include mottled leaves in patterns of green, yellow, and brown. Other signs include abnormal growth patterns, twisted stems, and gnarled leaves.

Flowers may fail to form naturally, and leaves can be curled and stunted.

Treatment

Like bacterial houseplant diseases, there are no cures for viral infections. Your plants may live for a while with the infection, but they will not thrive.

The biggest risk is that these infections can spread easily. So, even if you think your sick houseplant is rallying, you should remove and destroy it.

Prevention of Viral Houseplant Diseases

The best prevention for viral houseplant diseases is practicing good gardening hygiene. This means washing your hands and disinfecting your tools regularly. If you suspect any of your plants are ailing, sterilize your tools before using them on each plant.

Place new plants in quarantine before adding them to your indoor display — especially if you’ve purchased them from a nursery or home improvement center.

Other Types of Houseplant Diseases

Some problems that look like houseplant disease are really pest infestations. Mites, mealybugs, and even aphids can infect your plants, even though they’re indoors.

Signs of disease can reveal an underlying insect infestation. In some cases, a pest infestation will cause a subsequent infection. Sooty mold and bacterial wilt are two houseplant diseases caused by pests.

Flowers plant pots

Social Distancing for Houseplant Diseases

Just like other living things, plants can contract an illness and spread it to other plants. Without keeping a careful eye out for houseplant diseases, you could find your expensive and lovingly curated collection of specimens devastated by its own vegetative pandemic.

It’s a good idea to practice “social distancing” with your plants. If you suspect one is falling ill, isolate it from your healthy plants while you help it recover.

A short period of quarantine for new plants is also a good idea. Make sure newly purchased plants from that big box store has not brought home any pests or disease.

Most importantly, make sure your keeping your plants in optimal conditions for their species. Overwatering causes more houseplant diseases than any other factor. So, make sure you only water them as much as they require. It’s a good idea to group your plant together by water requirements to make this easier.

Too much water in the air can also exacerbate houseplant diseases. So, ensure they receive good air circulation with plenty of room to grow and thrive.