Symptoms

Yellow leaves — The most common symptom: almost always signals a watering or light issue.
Brown leaves — Crispy edges, dry tips or patches: different symptoms, different causes.
Black spots on leaves — Serious symptom: almost always an active fungal or bacterial disease.
Drooping leaves — Lost turgor: too much or too little water, or thermal shock.
Curled leaves — The plant is defending itself: thirst, harsh light or pests.
White spots on leaves — From powdery mildew to mealybugs: identifying the pattern is everything.
Spider mites — Yellow dots under leaves and fine webbing.
Scale insects — Small brown shields or white cottony clusters on stems and leaves.
Aphids — Small green, black or yellow insects that colonize shoots and buds.
Root rot — The most common cause of houseplant death.
Powdery mildew — White powdery coating spreading on leaves and shoots.
Fungus gnats — Small black gnats flying around houseplants.