What's Wrong with My Marijuana?

Cannabis is a heavy nitrogen feeder during vegetative growth. When nitrogen runs low, the plant pulls it back from its oldest leaves first, causing yellowing that starts at the bottom of the plant and climbs steadily upward toward the canopy.

Cannabis shows nutrient burn as dark green leaves with tips that go yellow, then brown and crispy, often curling down. Overfeeding floods the roots with dissolved salts that pull moisture out of the plant through osmosis, causing leaf tips to dry out even while the soil is wet.

Botrytis colonizes the dense interior of cannabis flower clusters where air cannot reach. It starts as gray or brown fuzzy growth deep inside a bud and can hollow out an entire cola before the outer surface shows any discoloration. The risk spikes in the final weeks of flowering when buds are tightest and resin is heaviest.

Overfeeding nitrogen causes cannabis leaves to claw downward at the tips, a pattern growers call the nitrogen claw. The whole leaf curves and the tips point straight down while the rest of the leaf stays dark green. It is most obvious on fan leaves in the middle and lower canopy.

Leaves close to an indoor grow light or in an outdoor spot with afternoon heat above 85°F cup upward and inward to reduce exposed surface area. Cannabis canopy leaves closest to the light source show it first, and the plant may also show bleached or light-yellow patches on the tops of exposed leaves.

Spider mites are the most common cannabis pest, especially in warm indoor grows with low humidity. They live on leaf undersides and cause pale stippling across the leaf surface. Fine webbing shows up between leaves and stems as the colony grows, and a large infestation can severely reduce photosynthesis before harvest.

Small black flies that emerge when you water or disturb the soil. Adult fungus gnats are mostly a nuisance, but larvae in the top few inches of growing medium feed on fine root hairs. Cannabis seedlings and plants in early veg are most vulnerable since root damage at that stage stalls growth.

Thrips leave silver or bronze streaking across leaf surfaces and deposit tiny black specks of frass on the undersides. They target new growth and can spread rapidly through a cannabis canopy. Damage early in veg reduces total leaf area and affects the structure of the plant heading into flowering.

Cannabis plants that do not get enough light stretch toward the source, producing long gaps between leaf nodes and weak, thin stems that cannot support buds later. Indoors this is the most common sign that the grow light is too far away or underpowered. Outdoors it happens when the plant is in partial shade instead of full sun.

Female cannabis plants produce banana-shaped pollen sacs inside their flower clusters when stressed, a survival mechanism that allows self-pollination. Stress triggers include light leaks during the dark cycle, heat, irregular photoperiod, or physical damage. Even one open pollen sac can seed an entire crop, converting resin energy into seed production.