Does magnesium compete with Potassium?

I see several fertilizers that have Potassium and Magnesium at the same time, so I'm wondering if I could safely mix magnesium sulfate with an NPK fertilizer.

Otherwise, would it be better to give them separately to the plant, within a week interval for example?

  • 1
    Mg + K is unlikely to be a problem, but you might have problems with Magnesium + Phosphate, if the soluble phosphates in the original fertilizer and the soluble magnesium salts react to form insoluble magnesium phosphate.
    – alephzero
    Commented Jul 22, 2021 at 19:55

1 Answer 1


NPK in not a composition. However fertilizer applications are relatively dilute compared to the mass of soil to which they are applied , so it is difficult to imagine a problem. Generally not a problem for a home owner depending on the exact levels and compositions of the NPK, but the mixed fertilizers can interact. I remember once getting a weak ammonia smell from dry mixed materials before application.

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