Problem Solver

Cold stress

Cold roots (below about 15 °C) slow everything down and can cause purple stems and phosphorus problems. Common in UK lofts and garages in winter.

Heat stress

Leaves fold up like a taco and droop in the afternoon. Keep the canopy in 20–27 °C and act fast above 28–30 °C.

High humidity (damp air)

Humidity above your week's chart range. It slows drying, invites powdery mildew and grey mould, and matters most in late flower.

Leaf curl and claw

Which way a leaf curls points to the cause: tips hooking down like a claw usually means too much nitrogen; upward taco means heat or light; downward and heavy means over-watering.

Light burn (light stress)

Top leaves nearest the light bleach pale or white, or turn yellow while lower leaves stay green. Raise or dim the light.

Light leaks in the dark period

Light getting into the tent during the 12-hour dark period in flower can stress the plant. Find and seal leaks.

Low humidity (dry air)

Humidity below your week's chart range: leaves dry at the edges, the plant drinks fast and spider mites get a head start.

Over-watering

The whole plant droops with fat, heavy, curled-down leaves and the medium stays wet for days. Let it dry back and water by weight.

Slow growth

The plant just isn't moving. Work through the basics: pH, EC, watering, climate and light, then the roots.

Stretching (leggy growth)

Tall, thin stems with long gaps between nodes. Usually not enough light or too much heat; some stretch in early flower is normal.

Under-watering

Thin, limp, papery leaves and a light container, with dry medium pulling away from the sides. Water slowly in stages.

Wilting and drooping

A drooping plant has a handful of usual causes. Start with the lift test: heavy means too wet, light means too dry, then check heat and roots.

Yellow leaves

Where the yellow is tells you the cause. Old leaves, new leaves, between the veins, at the tips or near the light: start here and follow the link.