The Best Way to Fertilize Potatoes to Maximize Harvests

Too much or too little fertilizer can significantly impact the size of your harvest. Are you fertilizing incorrectly?

Potatoes are a popular crop in home gardens for good reason. Unfortunately, many home gardeners mistakenly under-fertilize their plants, resulting in lower yields. They require different feeding than other garden plants, therefore let’s talk about the best technique to fertilize potato plants to get the biggest harvestable yield possible!

The answer to how much and when to fertilize your plants for best yield is not the same for all gardeners. Individual factors must be taken into account. It is necessary to discuss some of the science behind fertilization in order to properly understand it.

The Importance of Proper Nutrient Amounts

Plants require particular minerals for growth, and if any of these nutrients are deficient, the plant suffers in some way. Hidden hunger occurs when a nutritional deficit exists yet physical signs are not obvious on the plant. Future yield reductions occur as a result of concealed hunger.

This signifies that plants are getting enough nutrients to develop and aren’t showing signs of malnutrition, but it’s not ideal nutrition. The plants appear healthy—and they most likely are—but they don’t have any extra to invest in their future, and yields suffer as a result. 

However, feeding too much is also harmful since it can cause toxicities within the plant, and too much soil nitrogen or phosphorus is harmful to the environment.

A seedling with important nutrients.

Managing Nutrients in the Garden

Growing potatoes in the backyard differs significantly from commercial production, particularly in terms of nutrient management. Throughout the season, field-grown spuds are meticulously monitored and sampled to optimize plant nutrient concentrations and harvest numbers. This method is critical for profit maximization, but it is not always practicable in a home garden.

Commercial producers collect randomized petiole samples from their fields and analyze them for nutrient concentration (the petiole is the tiny stem that connects the leaves to the main stem) (in parts per million or ppm). They may now fine-tune their fertilization rates and adjust their fertilizer approach on the go as a result of the outcomes. As a result, they can avoid not just hidden hunger, which can dramatically reduce yields, but also overapplying fertilizer.

Tissue sampling requires more time and money than many home gardeners are willing to invest. However, there are techniques to optimize fertilizer management in your garden. Looking at the big picture and not applying fertilizer at a set pace is one of the most important factors.

Application Amounts

You should not fertilize potatoes based solely on online recommendations. You know, the ones that recommend applying 30 pounds of fertilizer per 1,000 square feet, or about one pound of fertilizer for every 10 feet of row. These solutions do not take into account the details of your circumstance. Application rates vary for a variety of reasons and should take soil sampling and testing into account.

Professional soil test results are crucial for growing potatoes in order to maximize your yield. They will tell you how much of each nutrient is present in the soil and how many more parts per million (ppm) you may expect to observe as the organic matter decomposes over the course of the season. It will also tell you the pH of the soil, which has a significant impact on nutrient availability.

Once you have these data, you may calculate the fertilizer application rates that are appropriate for your situation.

Transferring fertilized soil to a pot.

Optimal Fertilizer Ratio

Potatoes should also not be fertilized using a product that has a balanced N-P-K ratio. Because potatoes are root vegetables, they benefit from higher levels of phosphorus and potassium to stimulate tuber growth rather than nitrogen, which promotes vegetative growth. As a result, use a fertilizer with higher P and K levels than N, such as a 5-10-10 or an 8-24-24.

Other nutrients found in a good fertilizer include sulfur, copper, manganese, zinc, and boron. These nutrients are required in smaller quantities than N-P-K, yet they are equally important for healthy growth. When they are lacking, they have a negative impact on growth and yield.

Phosphorus and Potassium ratio.

Fertilizer Application Schedule

General recommendations instruct gardeners to apply a pre-plant and then fertilize monthly starting two weeks after planting. However, many extension professionals recommend applying fertilizer to the soil before planting and waiting on other applications until after tuber formation. Too much nitrogen early on may delay or inhibit tuber formation, reducing the size, specific gravity, and overall potato yield.

Fertilizer application with respect to stages of potato growth.

How the applications are split and the rate at the different times in the season varies depending upon the maturity type planted.

  • Early-season potatoes: Irish Cobbler, Caribe, Norland, Yukon Gold
  • Mid-season potatoes: Russet Burbank, Red Pontiac, Viking, Yukon Gem, French Fingerling
  • Late-season potatoes: Kennebec, Purple Peruvian, Butte, Katahdin, King Harry, Russet Norkotah


If you are growing early maturity spuds, apply two-thirds of the total nitrogen needed for the season as a pre-plant application. If you are growing medium to late maturity types, only apply one-third of the total nitrogen for the season before planting. Mix this pre-planting application into the soil as hills are formed for all types. 

A more significant nitrogen application at planting starts the seed potatoes off with plenty of nitrogen to kick start early vegetative growth. The soil nitrogen helps the plants rapidly grow and begin photosynthesizing.

After Tuber Formation

About six or seven weeks after planting, begin more regular fertilizer applications. Split the remaining nitrogen amount into two or three applications delivered about two weeks apart. These applications should be side-dressed, where the fertilizer is placed off to the hills’ side to prevent root damage from the fertilizer salts. 

Carefully cultivating around the plants and applying fertilizer.

As a general rule, never side-dress more than half the fertilizer applied at planting at any one time.

Other Tips for Optimizing Harvests

  • Make sure plants are adequately watered. Depending on the cultivar, they need 12 to 16″ of water during the growing season, and consistent watering is crucial when the tubers enlarge. Water the soil thoroughly once or twice a week to encourage the roots to grow deep into the ground.
  • Start with quality, certified disease-free seed potatoes suited to your growing zone. Do not use grocery store potatoes because they have been treated with sprout inhibitors for long-term storage.
  • Allow the eyes to sprout successfully before planting seed potatoes, and only plant sprouted pieces.
  • Keep the growing bed free of weeds by consistently pulling competitors by hand. Avoid hoeing or using herbicide to prevent damage to the developing tubers.
  • Chop off the tops of the vines 2 to 3 weeks before you plan to harvest. Once the plant stops actively growing, the skins toughen up a bit. A thicker skin makes the spuds easier to handle, and they store better. At this time, quit watering and fertilizing as well. 
  • Be mindful of crop rotation when planting potatoes. Choose a spot where you haven’t grown potatoes, tomatoes, eggplants, peppers, or tomatillos in three or four years.
  • Regularly scout your plant(s) for insect infestations and treat any problems quickly. 
  • Avoid using manure as a fertilizer immediately before planting or during the growing season. It tends to promote scab development on potatoes.
  • Potatoes prefer a soil pH between 5.0 and 6.0. If your soil acidity is too low, you can add gypsum; if the soil pH is too high, you can add lime as a soil amendment to make it more acidic.
Freshly harvested good quality potatoes.
Carley Miller
Carley Miller is a horticultural expert at Bustling Nest. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.
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