Leaf colour is a clue, not a diagnosis

Some nutrients can move from old leaves to new growth, so the old leaves fade first. Others stay put, so new tips, flowers, or roots show the shortage. Heat, salts, waterlogging, pests, and virus can copy the same pictures.

Look, then test. Do not buy iron because a leaf is yellow, or nitrogen because a neighbour did.

If two beds yellow the same way after opposite feeds, the cause is probably water, pH, or roots — not the last bag.

In this series

• Test soil before you buy another bag
• Irrigation is nutrient management
• pH can lock nutrients that are already in the soil
• Leaf colour is a clue, not a diagnosis
• Microbes and root fungi deliver what a bag cannot
• Return what you harvest so fertility does not walk off the field