Why Houseplants Get Sick: 10 Symptoms and What They Mean

A houseplant cannot complain, but it nearly always sends a signal: its leaves change colour or drop, or it stops flowering. The good news is that most problems are not mysterious diseases but growing conditions — light, watering, air and the pot. Here are 10 common symptoms and their likely causes.

Healthy plants delivered: potted houseplants.

View full-size photo

How to read the symptoms

The same sign can have several causes, so look at the whole picture: when the symptom appeared, what changed in your routine, and what the roots and soil look like. Start with the simplest factors — light and water.

Leaf problems

• Brown, dry tips. Usually dry air from radiators, uneven watering or salts building up from hard water and fertiliser. Use water that has stood for a day and flush the soil with a generous watering every few months.
• Pale or brown scorch marks. These appear when a plant moves suddenly from shade into direct sun. Acclimatise it gradually.
• Yellow or brown spots. These can signal fungal or bacterial leaf spot. On African violets, pale marks are often left by cold water on the leaves.
• Dropping leaves. A typical stress response to draughts, temperature swings or being moved. Ficus plants are especially sensitive to a change of place.

View full-size photo

Growth and flowering

• Plenty of leaves, few flowers. Too much nitrogen or too little light. Flowering needs good light and a feed richer in phosphorus and potassium.
• Small new leaves and wilting. Lack of light or nutrients, or a pot so tight that roots fill it completely.
• A long, pale stem. The plant is stretching for light: move it closer to a window or add a grow light.

Roots, coatings and distortion

• Soft brown or black roots. A sign of root rot from overwatering and poor drainage. Lift the plant, cut away affected roots, repot into fresh, well-drained mix and water less often.
• White powdery coating. Powdery mildew is a fungal disease. Remove affected leaves, move the plant away from others and treat with a fungicide as directed.
• Curled, distorted leaves. Often the work of sap-sucking pests such as aphids or thrips.

View full-size photo

Pests

Spider mites like warm, dry air and leave fine webbing and pale speckles on leaves. Mealybugs look like tufts of cotton wool in leaf joints, scale insects like brown bumps on stems, and thrips leave silvery streaks. Isolate an infested plant at once, rinse it under a lukewarm shower and treat it with a suitable insecticide exactly as directed, repeating until no new pests appear. Tiny black flies rising from the pot are fungus gnats; see how to get rid of fungus gnats.

Spider mites on houseplants: spotting and treating them

Mites under 0.5 mm long are almost invisible, so you notice the damage instead: tiny pale specks on leaves that merge into grey patches, fine webbing in leaf axils and shoot tips, and dull leaves that drop. Ficus, palms, dracaenas, roses and citrus suffer most in warm, dry air.

• Isolate the plant and rinse the leaves thoroughly under a lukewarm shower, especially the undersides.
• Raise humidity: mites dislike moisture.
• Treat with a miticide (ordinary insecticides often fail) 2–3 times, 5–7 days apart, to kill newly hatched mites.
• Check neighbouring plants: mites move easily from pot to pot.

View full-size photo

Mealybugs and sticky leaves

Mealybugs are white, fluffy, cotton-like blobs in leaf axils, on roots and under bulb scales. They are most common on orchids, succulents, dracaenas and citrus. Remove them with a cotton bud dipped in alcohol, wash the leaves with soapy water, then treat the plant and soil with a systemic insecticide.

Leaves that feel sticky, as if coated in syrup, carry honeydew, the sugary excretion of sap-sucking pests: scale, aphids, mealybugs or whitefly. Sooty mould, a black film, soon grows on it. So stickiness is a signal to inspect the plant and find the pest, not just to wipe the leaves.

View full-size photo

What to do first

• Move the plant away from others if you suspect pests or disease.
• Check soil moisture 2–3 cm down and inspect the roots.
• Assess the light: is the plant too far from a window or in harsh direct sun?
• Do not feed a sick plant — fertiliser is not a cure and can harm damaged roots.

We have collected the most common care mistakes in 10 ways to kill a houseplant, covered diseases of indoor roses separately, and explained gentle feeding in natural fertilisers for houseplants.

FAQ

Why are the lower leaves turning yellow?

If one or two old lower leaves yellow, that is natural renewal. If many leaves yellow at once, check watering and the roots.

Should I mist plants to fight dry air?

Misting raises humidity only briefly. A humidifier or a tray of wet pebbles is more reliable.

Can a plant with rotten roots be saved?

Often, yes, if some healthy pale roots remain: keep those, cut away the rest and repot into fresh mix.

Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.

About the author →