Nitrogen deficiency
An even yellowing of older, lower leaves with slow, weak growth, caused by a lack of available nitrogen.
Also known as: Yellowing of old leaves, Hungry plants
Symptoms and identification
The oldest leaves turn pale green and then evenly yellow, starting at the bottom of the plant. New growth is small and pale, stems are thin, and plants produce fewer flowers and fruit.
Causes
Old or exhausted potting mix, frequent heavy watering that washes nutrients out, or fresh woody material such as sawdust that locks up nitrogen as it breaks down.
Organic treatment
Water in a feed of diluted cow dung slurry, compost tea or a liquid seaweed and fish fertilizer. Top-dress with vermicompost. Plants usually green up within one to two weeks.
Prevention
Repot or top-dress containers with fresh compost each season. Feed leafy crops regularly and avoid mixing raw sawdust or wood chips into the soil.
Chemical treatment (use with care)
A small dose of a balanced or nitrogen-rich water-soluble fertilizer, used at the label rate, gives a quick response.