The potato plant is a heavy feeder, requiring a steady and balanced supply of nutrients throughout its growing cycle. Successful potato cultivation depends heavily on precise application timing, more so than just fertilizer quantity. Scheduling fertilizer to align with the plant’s distinct growth phases ensures energy is directed toward tuber formation rather than excessive foliage growth. Understanding the “when” of feeding is as important as the “what” to maximize yield.
Soil Preparation and Foundational Nutrient Requirements
Establishing the correct soil environment begins well before planting. Potatoes prefer a slightly acidic soil pH, ideally ranging from 5.0 to 6.5, which minimizes the risk of common scab. Soil testing determines existing nutrient levels and pH, informing necessary pre-planting amendments. If the soil is too alkaline, sulfur can be added to lower the pH; however, lime should be avoided within two years of planting as it raises pH and promotes scab development.
Potatoes require relatively high amounts of phosphorus (P) and potassium (K), but only moderate nitrogen (N) initially. Phosphorus is needed early for strong root and stolon development, the underground stems where tubers form. Potassium is absorbed in large quantities throughout the season, supporting plant health, water regulation, and tuber quality. Pre-planting incorporation of aged compost or well-rotted manure improves soil structure and provides a slow-release source of nutrients.
The Timing of Potato Fertilization
Fertilizer application is segmented into three key periods, synchronizing nutrient delivery with the plant’s metabolic demands. The first application occurs at planting, placing a low dose of balanced fertilizer in a band a few inches to the side and slightly below the seed piece. This starter fertilizer provides readily available nutrients, especially phosphorus, encouraging rapid root establishment.
The second application is timed around the first hilling, typically when shoots emerge and reach six to eight inches tall. This marks the start of the vegetative growth phase, requiring a boost of nitrogen to produce a large, healthy canopy. This process, known as “side dressing,” involves placing the nutrient blend next to the row before mounding soil around the stems. This application supports the leaf mass necessary for photosynthesis to power tuber production.
The third feeding period aligns with the initiation of tuber set, often coinciding with the second hilling when plants are ten to twelve inches high. This stage shifts the plant from vegetative growth to tuber bulking, creating the highest demand for potassium and phosphorus. Adequate nutrition during this window, generally 20 to 60 days after emergence, directly influences the final size and number of potatoes harvested.
Selecting and Applying Fertilizer Types
Fertilizer ratios change throughout the season to match the plant’s physiological needs. While a balanced blend like 15-15-15 is suitable for initial planting, the plant quickly shifts to needing lower nitrogen and higher phosphorus and potassium. Growers often use formulas heavy in the last two numbers, such as 5-10-10 or 3-5-5, because excess nitrogen promotes foliage growth at the expense of tuber development.
Application technique, especially side dressing, is important. Granular fertilizer should never be poured directly onto the stems or leaves, as this causes burn. Instead, apply the fertilizer in a narrow band along the row, a few inches away from the plant. Incorporating it into the soil during hilling ensures nutrients are near the shallow root system and prevents developing tubers from turning green.
For organic sources, bone meal provides phosphorus for initial planting, while alfalfa meal or compost offers slow-release nitrogen. Potassium can be supplied using wood ash or organic potash sources. Focusing on potassium sulfate rather than potassium chloride can lead to better dry matter content in the tubers.
Addressing Nutrient Deficiencies and Late-Season Needs
Monitoring the potato canopy allows for timely correction of nutrient imbalances and prevents yield loss. Nitrogen deficiency is identified by chlorosis, or the yellowing of older, lower leaves, as nitrogen is mobile and moves to newer growth. Conversely, phosphorus deficiency causes older leaves to develop a purplish discoloration, while yellowing in younger leaves with green veins may indicate a lack of micronutrients like iron or sulfur.
As the season progresses, significantly reduce or halt nitrogen applications to encourage tuber maturation. Excessive nitrogen late in the season delays the plant’s natural senescence, keeping foliage green but impairing storage quality by preventing skins from setting properly. When the plant nears maturity, typically 90 to 120 days after planting, the foliage will naturally begin to yellow and die back.
This yellowing signals that the plant is allocating its remaining energy to the tubers, and supplemental feeding should stop completely. Maintaining consistent soil moisture during the tuber bulking phase is necessary for nutrient transport and prevents misshapen tubers. Reducing irrigation as the foliage dies back helps toughen the potato skins, preparing them for harvest.