Sulfur deficiency

📖 Overview

Sulfur deficiency is a nutrient problem that strikes the youngest leaves first, turning them pale yellow while older foliage stays green—this is the opposite of nitrogen hunger, which yellows from the bottom up. The entire leaf blade develops a uniform, soft yellow tone rather than the spotty pattern you'd see with disease or iron deficiency. What makes sulfur deficiency tricky is that it often goes unnoticed at first because it affects only the newest growth; by the time you spot it clearly, the plant may already be struggling.

This deficiency matters most to brassicas like cabbage and broccoli, alliums such as garlic and onions, and corn, where sulfur is essential for building proteins and chlorophyll. A sulfur-starved plant grows slowly, produces smaller yields, and becomes more susceptible to pest pressure. In temperate regions, the problem surfaces most often between May and August, when rapid spring growth has exhausted soil reserves and heavy rain has leached sulfur from sandy or acidic soils. It's also common in gardens with alkaline soil (pH above 7), where sulfur compounds lock up and become unavailable to roots.

The first sign to watch for is pale, uniform yellowing of the leaf veins on brand-new leaves at the top of the plant—quite different from iron chlorosis, where the veins stay green while the spaces between turn yellow. If you're unsure whether you have sulfur or nitrogen deficiency, look at which leaves yellowed first: sulfur hits young leaves; nitrogen hits old ones.