Yellowing Ponderosa Pines: Sulfur Deficiency, Not Iron

Three ponderosa pines in Montana have yellowed needles for over a year. Soil test: high iron (13,000 mg/kg), near-zero sulfur. Initial advice misread as iron deficiency; corrected to sulfur deficiency.

Sulfur's Role

Sulfur is essential for chlorophyll production, amino acids, and protein synthesis. Deficiency shows on young needles first (yellowing).

Correction

• Apply ammonium sulfate (21-0-0, 24% S) at 1 lb per inch of trunk diameter.
• Spread under canopy (not within 1 ft of trunk), water in.
• Repeat now, spring, then every 3 months until color returns.
• Do NOT use weed-and-feed (herbicide damages roots).

Granular sulfur also works; ask nursery for rate. Ammonium sulfate provides both N and S.