Diagnose by symptom
Yellow leaves
Yellowing leaves can have many causes — from iron deficiency through vascular diseases to sap-sucking pests. The most common:
Diseases
Iron chlorosis (lime-induced chlorosis)
The symptom affects acid-loving plants — hydrangea, rose, rhododendron, blueberry and others — grown on alkaline or calc…
DiseaseVerticillium wilt
The first symptom is a sudden wilting and drying of leaves on individual branches or on one side of the crown, while the…
DiseaseFusarium wilt
The soil-borne fungus infects the root system and enters the vascular bundles, blocking the flow of water within the pla…
DiseaseDowny mildew
Yellow or angular (vein-bounded) spots on the upper leaf surface, matched underneath by a grey-violet or brown coating o…
DiseasePotato and tomato late blight
Dark-brown, spreading spots on the leaves (often with a lighter margin and a whitish coating on the underside in humid c…
Pests
Aphids
Small (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leave…
PestSpider mites
Tiny (0.3–0.5 mm) arachnids, hard to spot with the naked eye, feeding on the underside of leaves. Symptoms: fine, pale s…
PestMealybugs
Insects covered in a white, cottony, waxy coating, gathering in leaf axils, at the base of shoots and on the underside o…
Frequently asked questions
Why are my plant's leaves turning yellow?
The most common cause is overwatering and root rot, which block uptake of water and nutrients. Yellowing also comes from deficiencies (nitrogen – older leaves, iron – young leaves, i.e. chlorosis), too little light, and spider mites. A few yellow leaves at the base are usually natural aging.
Do yellow leaves mean I'm overwatering?
Very often yes – with overwatering the lower leaves yellow first, the soil stays constantly wet, and roots may be brown and foul-smelling. Check soil moisture with a finger 2–3 cm deep and hold off watering until it dries. If the soil is dry, the cause is more likely a nutrient or light deficiency.
How do I tell chlorosis from nitrogen deficiency?
With nitrogen deficiency the oldest lower leaves yellow evenly first, because the plant moves nitrogen to young growth. Iron chlorosis affects young leaves at the top: the blade yellows while the veins stay green (interveinal yellowing). Iron chlorosis worsens on overly alkaline soil.