Why are my plant leaves turning yellow?
Yellowing is a symptom of dozens of causes, but the pattern narrows it fast. Which leaves yellowed first — oldest or youngest — separates the mobile nutrients from the immobile ones, and whether the veins stayed green separates deficiency from disease.
The one observation that decides it
Ask two questions. First: oldest leaves or youngest? The plant moves nitrogen, magnesium and potassium out of old leaves to feed new growth, so those deficiencies start at the bottom; iron and manganese cannot move, so they start at the top. Second: did the veins stay green? Green veins on a yellow leaf is interveinal chlorosis and points to a nutrient. Uniform yellowing with wilting, especially on one side of the plant, points to a vascular wilt or root problem instead.
Start from the plant in front of you
15 things it could be
Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.
Yellowing and wilting often on one side of the plant or one branch, progressing upward; brown discoloration inside the lower stem when cut; eventual collapse despite moist soil.
Conditions: 25–34°C · humidity ≥60%First move: Remove affected material nowLeaves yellow and die back from the tips while the plant is still growing, and the whole plant lifts out easily. The base of the bulb is covered in a dense white, fluffy mat studded with poppy-seed-sized black sclerotia.
Conditions: 10–24°C · humidity ≥80%First move: Remove affected material nowLeaves are small, pale and sparse, and the plant wilts in warm weather despite wet soil. Whole branches die back one at a time. Cut the bark at the base and the tissue underneath is brown or reddish instead of white-green, often with a sharp line between healthy and dead.
Conditions: 15–30°C · humidity ≥90% · wet leaves / rainFirst move: Remove affected material nowSeen on: Asparagus, Blueberries, Rosemary, Thyme, Oregano, Sage and 1 more
Stunting, wilting in midday heat, and yellowing of older leaves above ground; swollen, distorted club-shaped roots below ground that rot and smell.
Conditions: 12–27°C · humidity ≥70% · wet leaves / rainFirst move: Fix the cause, not the leafSeen on: Cabbage, Radishes, Kale, Broccoli, Cauliflower, Brussels sprouts and 1 more
Plants wilt in the heat of the day despite adequate water, grow slowly and yellow between the veins. Lifted roots carry irregular swellings and galls fused into the root tissue — unlike legume nitrogen nodules, these cannot be rubbed off.
Conditions: 18–30°CFirst move: Fix the cause, not the leafSeen on: Carrots
Fine pale stippling or bronzing of leaves, delicate webbing on undersides and growing tips, and leaf drop in heavy infestations; tiny moving dots visible with a lens.
Conditions: 27–40°C · dry air ≤55%First move: Treat, then re-check in 5–7 daysSeen on: Aubergines, Marigolds
V-shaped yellow wedges at leaf margins, wilting during the heat of the day, and tan-to-brown streaking in the wood when a stem is cut. Often progresses slowly over a season.
Conditions: 18–27°C · humidity ≥60%First move: Remove affected material nowSeen on: Aubergines
Wilting despite obviously wet soil, yellowing of the lower leaves, and leaf drop. Stems may show soft brown rot at the base, and the soil smells sour or of rotten eggs. Growth stops entirely and the plant becomes an easy target for Phytophthora.
Conditions: humidity ≥90% · wet leaves / rainFirst move: Fix the cause, not the leafYellowing between the veins of the youngest leaves while the veins stay green (interveinal chlorosis); in severe cases new leaves turn nearly white with browning margins.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leafSeen on: Blueberries, Hydrangeas
Uniform pale green to yellow colour starting on the oldest lower leaves and moving up, spindly slow growth, and small pale new leaves; older leaves may drop early.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leafYellowing and browning (scorch) of leaf margins on older leaves while the centre stays green, weak stems, and poor, uneven fruit colour and ripening.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leafWhite to grey powdery coating on the upper surface of leaves and stems, later yellowing, curling and premature leaf drop. Fruit may be stunted or sun-scorched as the canopy thins.
Conditions: 15–28°C · humidity ≥60%First move: Treat, then re-check in 5–7 daysSeen on: Cucumbers, Zucchini, Peas, Pumpkins, Apple trees, Grapes and 15 more
Clouds of tiny white moth-like insects under leaves; yellowing, wilting and weakened plants; sticky honeydew and black sooty mould on lower leaves.
Conditions: 21–33°CFirst move: Treat, then re-check in 5–7 daysYellowing between the veins of older lower leaves while the veins stay green, often with reddish or purple tints and curling margins, progressing upward over time.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leafYellowing between the veins of the youngest and middle leaves, with the veins themselves and a band either side staying green — a broader green edging than iron deficiency shows. Beetroot leaves turn red-purple; peas develop the brown "marsh spot" inside the seed.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leaf