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Potassium

Quick definition

A macronutrient essential for overall plant vigor, disease resistance, water uptake, and fruit quality, represented by the third number in the NPK ratio.

In plain terms

Potassium (K) is the third number in NPK. It improves overall plant health, strengthens disease resistance, improves drought tolerance, and enhances fruit flavor and color. Deficiency causes leaf edge browning and weak plants. Most soils have adequate potassium; deficiency is uncommon but possible in heavily leached sandy soils.

Why this matters

Understanding potassium helps optimize plant vigor and disease resistance. Adequate potassium means stronger plants and better fruit quality.

In practice

Examples

Garden fertilized with high-nitrogen (10-3-3); plants weak, disease-prone; switching to 10-10-10 improves vigor.
Tomato fertilized with 8-8-8 (adequate K); stronger plants, better disease resistance, better flavor.
Potassium-deficient plant: leaf edges brown; plant weak; potassium fertilizer restores vigor.
Fruit quality improves with adequate potassium; enhanced sweetness and color.

Practical applications

Use balanced or adequate-potassium fertilizer (10-10-10 or higher).
Wood ash is a good organic source of potassium for gardens.
Potassium rarely needs supplementation; most soils have adequate levels.
Adequate potassium improves plant disease resistance and drought tolerance.
Monitor plant vigor; weak plants may benefit from balanced fertilizer.

Connected terms

Learn these first

Macronutrient NPK Ratio Disease Resistance