What Kind of Fertilizer Is Needed for Potato Plants?

Nitrogen

• In many areas, nitrogen is the most limiting soil nutrient for potatoes. Sandy soil often has a low nitrogen content. Without sufficient nitrogen, potato plants have stunted growth, leaf yellowing and poor yields. Nitrogen is the first number in a fertilizer grade.

Phosphorus and Potassium

• Phosphorus and potassium are the next most limiting nutrients in some soils. A soil test correctly identifies soils deficient in phosphorus and potassium. The amount of phosphorus is the second number in a fertilizer grade and potassium is the third number. Different potato varieties or cultivars often have different nutrient requirements. Early producing potato varieties might have different requirements than late maturing varieties.

Other Essential Nutrients

• In some soils, the secondary plant nutrients are deficient. Secondary plant nutrients include sulfur, magnesium and calcium. In addition, one or more of the essential micronutrients might cause problems with potato production and quality. The essential micronutrients include boron, chlorine, copper, manganese, iron, molybdenum and zinc. Each nutrient has specific deficiency symptoms for potato plants. Fertilizers are available to address any nutrient deficiency once the deficiency is identified.

Fertilizer Grades

• In general, 2.5 to 3 pounds of an 8-16-16, 10-20-20 or a similar fertilizer is sufficient for 100 square feet of garden soil or a 33-foot row of potatoes. A well-fertilized garden area may only require 3 pounds of a 10-10-10 fertilizer for a 33-foot row of potato plants.

How to Apply Fertilizer

• In many gardens, the fertilizer is worked into the soil by rototilling or spading at the time of planting. Less fertilizer is often required if the fertilizer is applied as a band close to the potato sets. A band of fertilizer is placed about 2 inches below and 2 inches to the side of the seed pieces. In soil with low fertility, additional fertilizer may be applied when the potato plants emerge from the soil and about four weeks later.