Why is my plant not growing properly?
A plant that will not grow, with no dramatic symptom to point at, is the hardest case in the database. Work from the bottom up: roots, then soil, then nutrition, and only then consider a virus.
The one observation that decides it
Lift one plant and look at the root ball before doing anything else, because a root problem explains almost every above-ground symptom and no leaf treatment can reach it. Healthy white roots filling the soil move the question to nutrition or light. Roots that are brown, sparse, galled or clubbed give you the answer directly. If the roots are fine and the feeding is right, uneven stunting with mottled foliage on a single plant points to a virus.
Start from the plant in front of you
11 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.
Leaves 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
Yellow mosaic mottling and puckering of young leaves, which often become narrow and strap-like. Plants are stunted, flowers are streaked or malformed, and cucumber fruits are warty, pale and bitter.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowUpward curling and cupping of leaves, yellowing of margins, severe stunting with bushy shortened growth, and heavy flower drop with little or no fruit.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowMottled light and dark green or yellow mosaic patterns on leaves, distortion, puckering and stunting; fruit may be mottled, lumpy or fail to set.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowMottled light and dark green leaves, crinkled and often with dark necrotic streaks down the stems and leaf veins. Plants are noticeably shorter than healthy neighbours and drop their lower leaves early. Tubers may show sunken rings.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowSeen on: Potatoes
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
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 leafRounded, rough, woody galls at the soil line, on roots, or on stems, starting soft and cream-coloured then hardening and darkening; reduced vigour and stunting.
Conditions: 20–30°C · humidity ≥60%First move: Treat, then re-check in 5–7 daysSeen on: Rhubarb
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 leafDull, dark blue-green leaves that later develop a distinctly purple or reddish cast, starting on the oldest leaves and the undersides. Growth is stunted, stems are thin, flowering and fruiting are delayed, and roots are sparse.
Conditions: ≤12°CFirst move: Fix the cause, not the leaf