Edema

What you see

Small water-soaked bumps on the leaf underside that turn corky, tan or rust-coloured and rough to the touch, sometimes in lines along the veins. Leaves may yellow and drop. The bumps do not rub off and there is no mould.

Conditions

Roots taking up water faster than the leaves can transpire it - warm wet soil with cool humid air. Classic in a conservatory or on a windowsill after a heavy watering on a dull day, and in overwatered succulents.

Treatment

Reduce watering and water in the morning rather than the evening. Increase light and air movement. Damaged leaves will not recover but new growth will be clean.

Prevention

Water in the morning, keep humidity down, space plants for airflow, and give plenty of light. Never water a plant heavily going into a cool dull spell.

Months: November, December, January, February, March, April

Plants

Pelargonium, Succulent, Tomato, Camellia, Cabbage, Ivy

Remedies

Not recorded — the field is blank rather than guessed.

The thing people get wrong

This gets diagnosed as rust, scale insects or spider mite damage and treated repeatedly with sprays, none of which do anything, because there is no organism involved at all - the leaf cells simply burst from taking on more water than the plant could exhale. The tell is that the bumps are the leaf's own tissue: you cannot scrape them off, and there is never any mould, webbing or movement.