How do I work out what's wrong with my plant?
A diagnostic method for sick plants — what yellowing, wilting, spots and holes each tend to mean, and what to check first.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 2 min
Short answer
Check the roots and the watering before anything else, because overwatering and underwatering cause the majority of plant problems and look confusingly similar. Then look at the pattern: uniform yellowing suggests light or nutrients, spots suggest fungal disease, and holes suggest something eating it.
Plant diagnosis looks mysterious but follows a short decision tree. Most problems are cultural — water, light, drainage, feeding — rather than pest or disease. Checking those first avoids treating a watering problem with a fungicide.
Step by step
- Check the soil moisture before anything else.Push a finger 5cm in. Soggy and smelling sour means overwatering; bone dry and shrunk from the pot edge means underwatering.
- If in doubt, look at the roots.Healthy roots are firm and pale. Brown, soft, smelly roots are rot — that's the answer, and it's the commonest one.
- Note the pattern of the damage.Uniform across the whole plant suggests a cultural cause. Patchy or spotted suggests disease. Chewed edges or holes suggest a pest.
- For uniform yellowing, consider light, nitrogen and overwatering.Lower leaves yellowing first often means nitrogen or overwatering; whole-plant pale growth often means insufficient light.
- For spots and blotches, look for fungal disease and improve airflow.Fungal problems thrive in still, humid conditions and on wet foliage. Water at the base, not over the leaves.
- For holes and chewed edges, look for the culprit — including at night.Slugs and snails feed after dark. Caterpillars and vine weevil larvae hide. Check undersides of leaves for aphids and eggs.
- Check the growing conditions against what the plant actually wants.A sun-loving plant in shade or an acid-loving plant in alkaline soil will decline slowly regardless of care.
- Change one thing at a time and give it two or three weeks.Plants respond slowly. Changing everything at once tells you nothing and often makes things worse.
Tips
- Photograph the problem with a date. Whether it's spreading is often more diagnostic than what it looks like now.
- Yellow leaves that have already yellowed won't turn green again. Judge success by new growth, not by old leaves recovering.
- Most 'mystery' houseplant deaths are root rot from a pot without drainage. Check that first, every time.
- A plant that declined suddenly after being moved is usually reacting to the change in light — give it several weeks before intervening further.
Common mistakes
- Watering a wilting plant without checking the soil — Root rot from overwatering causes identical wilting, and more water makes it worse.
- Reaching for a treatment before diagnosing — Most problems are cultural. Fungicide won't fix a drainage problem.
- Changing several things at once — You can't tell what helped, and plants dislike multiple simultaneous changes.
- Expecting damaged leaves to recover — They won't. New growth is the only indicator that matters.
Questions people ask
Why are my plant's leaves turning yellow?
Most often overwatering, especially if the lower leaves go first and the soil stays wet. Other causes are insufficient light, nutrient shortage, or simply an old leaf being shed. Check the soil and roots first.
How do I tell overwatering from underwatering?
Both cause wilting. Overwatered soil is wet and may smell sour, and the roots are brown and soft. Underwatered soil is dry, often shrunk away from the pot sides, and the plant perks up within hours of watering.