Most Common Houseplant Problems

by Brett Kerley

Indoor plants bring beauty and improved air quality to homes, but they can also be susceptible to various diseases and environmental problems. Edmonton’s cold winters and dry indoor conditions create unique challenges for plant health. Many plant owners move their plants outdoors during the summer for better growth, and bring them back inside in the fall. This transition can sometimes introduce new pests and diseases. Below are some of the most common diseases and problems faced by indoor plants in the Edmonton area, along with tips on prevention and treatment.

Symptoms: White or grayish powdery spots on leaves and stems. Leaves may become distorted, yellow, or drop prematurely. Causes: Poor air circulation, high humidity, and overcrowded plants. Powdery mildew thrives in warm, dry conditions with limited airflow. Common Locations: Plants placed too close together on shelves or in corners with poor airflow. Also common when plants are brought inside after summer, as spores can be transferred from outdoor air. Prevention & Treatment: Ensure good airflow around plants by spacing them properly. Avoid excessive watering, especially in cooler months. Remove affected leaves immediately. A diluted solution of baking soda (1 teaspoon per quart of water) with a drop of dish soap can be sprayed on leaves to help prevent the spread. Neem oil or a fungicidal spray may also be effective.

Symptoms: Yellowing leaves, mushy roots, and a foul smell from the soil. Plants may wilt and exhibit stunted growth. Causes: Overwatering and poorly draining soil. Root rot is typically caused by fungal infections due to excessive moisture around the roots. Common Locations: Plants placed in decorative pots without drainage holes or kept in low-light areas where soil stays damp for too long. It can also occur after bringing plants back inside if they were exposed to excessive rain outdoors. Prevention & Treatment: Use well-draining soil and pots with drainage holes. Water only when the top inch of soil is dry, and avoid letting water sit in saucers. If rot has set in, remove the plant from its pot, trim away affected roots with sterilized scissors, and repot it in fresh, dry soil. Applying a fungicide can help prevent reinfection.

Symptoms: Yellow or brown spots on leaves, webbing on undersides of leaves, and general plant decline. Causes: Dry indoor conditions and poor plant maintenance. Spider mites reproduce rapidly in warm, dry environments. Common Locations: Plants near heating vents, fireplaces, or in sun-drenched windows where the air is particularly dry. They can also be brought on from outdoor plants when transitioning them back inside. Prevention & Treatment: Increase humidity by using a humidifier or misting plants regularly. Wipe leaves with a damp cloth to remove mites. Treat infestations by spraying plants with insecticidal soap, neem oil, or a mixture of water and mild dish soap. Severe infestations may require repeated treatments every few days.

Symptoms: Tiny black flies hovering around soil, slow plant growth, and yellowing leaves. Causes: Overwatering and organic material buildup in soil. Fungus gnat larvae feed on plant roots, causing damage. Common Locations: Plants kept in consistently moist conditions, particularly those near kitchen sinks or bathrooms. Also, plants that were kept outdoors in summer and brought in with damp soil may develop a gnat infestation. Prevention & Treatment: Allow the top layer of soil to dry out between watering to disrupt the gnat life cycle. Use sticky traps to catch adult gnats. Applying beneficial nematodes or a diluted hydrogen peroxide solution to the soil can help eliminate larvae. Consider switching to a soil-free medium for propagation. For more information see article ‘Fungus Gnats on House Plants.

Bordo Copper Spray

Safer’s 3-in-1 Garden Spray

Symptoms: Brown, black, or yellow spots on leaves that may spread and cause leaf drop. Some spots may have a yellow halo. Causes: Fungal or bacterial infections due to excessive moisture, poor air circulation, or contaminated gardening tools. Common Locations: Plants in overly humid areas such as bathrooms or placed too close to each other in dense arrangements. Outdoor exposure during summer can introduce fungal spores, leading to outbreaks indoors. Prevention & Treatment: Avoid overhead watering and water at the base of the plant. Improve airflow by trimming overcrowded foliage. Remove affected leaves and dispose of them properly. Apply a copper-based fungicide (Bordo) or bactericide (Safer’s 3-in-1 Garden Spray) if the infection is severe.

Leggy Growth on Vine

Symptoms: Stretched-out stems with sparse leaves, making the plant appear weak and elongated. Causes: Insufficient light, leading plants to stretch toward the nearest light source. Common Locations: Plants placed in low-light corners, far from windows, or in rooms without adequate artificial lighting. Plants that thrive in bright outdoor conditions may struggle to adjust indoors and become leggy. Prevention & Treatment: Move plants to a brighter location with indirect sunlight. Supplement with grow lights, especially during Edmonton’s darker winter months. Rotate plants regularly to encourage even growth. Pruning leggy stems can help promote bushier growth.

Symptoms: Leaves that appear limp, weak, or lifeless. Causes: Underwatering, overwatering, root rot, temperature stress, or shock from transplanting. Common Locations: Plants placed near drafty windows, air conditioning units, or heating vents where temperature fluctuations are common. Can also occur due to shock when plants are moved indoors after thriving outside. Prevention & Treatment: Check soil moisture before watering; if the soil is dry, water the plant thoroughly. If it is soggy, allow it to dry out before watering again. Maintain a consistent indoor temperature and protect plants from drafts, heating vents, or sudden temperature changes. If transplant shock is suspected, provide the plant with optimal care and avoid excessive handling.

Edema On Plant

Symptoms: Also known as oedema, edema is not a disease, nor a symptom of a virus, insect damage or of bacteria. Instead it is a disorder that is usually influenced by environmental issues. Basically, edema occurs when plants take up more water than needed for transpiration (water loss) from the leaves, which causes the cells inside the leaves to rupture resulting in the marking on the leaves. Water-soaked blisters on leaves that turn brown or corky over time. Causes: Overwatering, fluctuating humidity levels, or inconsistent watering practices leading to imbalances in water uptake. Common Locations: Plants placed near humidifiers or in rooms where humidity levels fluctuate frequently. Moving plants from outdoor humidity to dry indoor air can trigger edema. Prevention & Treatment: Maintain a consistent watering schedule and avoid overwatering. Improve airflow around plants by using fans or spacing them apart. Adjust humidity levels gradually to prevent sudden changes that stress the plant.

Back in 2012 Health Canada took compliance action to remove Neem oil from the market as a pesticide, however you can still purchase Neem oil as a herbal product in health stores or on Amazon, just not at your local garden centre.

*WARNING* Neem oil does not harm birds, but it may harm beneficial insects and soil-loving creatures, such as bees, butterflies, lady beetles, and earthworms. For that reason, it should only be used when you have a definite issue with one of the harmful insects or diseases. Basically, I only recommend using it on indoor plants.

How to Mix Neem Oil

Neem oil will not readily combine with water and needs an emulsifying agent, like a mild dish detergent, to effectively mix the oil. Only make enough to use that day, as it doesn’t keep well. I’ve also added a few drops of peppermint essential oil.

Recipe: Mix 2 teaspoons (10 mL) of neem oil, 1/4 teaspoon (1.25 mL) of dish detergent, and 1 litre of warm water in your sprayer. Mix thoroughly.

Taking care of indoor plants in Edmonton requires attention to watering habits, light exposure, and humidity levels. Many plant owners enjoy placing their plants outdoors during the summer, which can boost growth and vigor, but the transition back inside in the fall must be managed carefully to avoid pests and diseases. Regularly inspecting your plants for early signs of issues can help prevent serious problems. With proper care, your indoor plants can thrive and continue to brighten your home, even through the harsh Edmonton winters.

Until next time, may your plants continue to grow and inspire. Happy gardening!