Managing Manganese Deficiency in High-pH Soils: Chelates vs. pH Adjustment

A New Mexico gardener with soil pH 7.9–8.2 and high lime content uses FeEDDHA chelated iron successfully but also has low manganese. He asked if specific manganese chelates work better at high pH, and which acidifying amendment is best.

Chelated Manganese Products Are Similar

No special high-pH manganese chelate exists; any quality chelated Mn (e.g., Peters STEM) works. However, added Mn is often quickly displaced by iron, giving the opposite of the desired effect.

Lowering pH Is More Effective

Target pH 6.5–7.0 to unlock native manganese and iron. Options:

• Aluminum sulfate – cheap, fast, also supplies aluminum for blue hydrangeas.
• Sulfur, ferrous sulfate, ammonium sulfate – all work; choose the most economical. Avoid ammonium sulfate after July 1 to prevent late-season growth.

Quick Fix for a Few Plants

Dissolve chelated manganese tablets (from a health food store) in water and apply to individual plants if only a small area needs it.