Iron deficiency
Symptoms
Iron is involved in chlorophyll production and helps absorb nitrogen. When deficient — the veins of the top leaves begin to yellow or whiten, while the veins themselves remain green. If the soil pH > 6.8, plants have difficulty absorbing iron.
Control and prevention
Adjust soil pH, use chelated iron.
Related problems
Similar symptoms might indicate a different cause — compare them.
Nitrogen deficiency or excess
When deficient — growth slows down, old leaves lose color, newly growing leaves are yellow-green. Nitrogen is quickly broken down or washed out by water. In case of excess — tomatoes grow many leaves, but bloom little and set fruit sparsely.
Magnesium deficiency
Magnesium is an important part of chlorophyll. When it is deficient, the veins of old leaves begin to yellow, while the veins themselves remain green. Later, the symptoms spread to young leaves, which begin to wither.
Potassium deficiency
Potassium is responsible for metabolism in the plant. When deficient — leaves begin to wither, deform, yellow, the stem weakens, fruits fall prematurely. When a young plant is deficient — it grows deformed, the edges of older leaves dry out.