fertilizing potatoes

Fertilising Potatoes: the key to big yields

If you are growing potatoes for the first time, you may be wondering if fertilising potatoes is a good idea. Like all living plants, potato plants need adequate nutrients to grow and produce large tubers. Namely, potatoes need nitrogen, phosphorus, and potassium, the three nutrients denoted in the NPK ratio on a bag of fertilizer.

The amount of fertiliser your potatoes need depends on your soil’s condition and the potatoes’ growth stage.

Should I add fertiliser to my potatoes?

Yes, usually, it is a good idea to add fertiliser to your potatoes. Many gardeners apply fertilizer to their potatoes at planting time by incorporating the fertiliser into the soil. This gives the plants an early boost and ensures they have the nutrients they need to get off to a good start.

Side-dressing the potatoes with fertilizer when they are 4 to 6 inches tall and ready to be hilled is also standard practice. This means sprinkling a narrow band of fertilizer along the row of potatoes and working it into the soil with a hoe or other garden tools before mounding the soil around the base of the potatoes as you hill them.

The University of Minnesota Extension (UMN) recommends repeating the side dressing and hilling procedure again in two weeks. Other sources, like Backyard Vegetable Gardening, recommend fertilizing potatoes once a month after the first side dressing.

What are the benefits of adding fertilizer to potatoes?

Fertilizer provides your potato plants with the nutrients they need to thrive and produce a large crop of healthy tubers. The amount of fertilizer you need for your garden depends on the condition of your existing soil.

fertilizing potatoes in a field
When potatoes receive the optimum nutrients they will thrive and produce an impressive yield of potatoes.

The best way to assess the fertilizer needs of your garden soil is with a soil test. Many university extensions offer soil testing services for a nominal fee. The soil test will reveal the amount of the available nutrients in your soil and provide you with detailed instructions for amending the soil — including the amount of fertilizer it needs. Take a look at this article to find out more about what type of soil potatoes like best.

What type of fertilizer should I use?

There appear to be two schools of thought on the proper balance of nutrients for potatoes. While some sources (like UMN) recommend using a balanced formula, such as 10-10-10, others, like Backyard Vegetable Garden, recommend a formula with lower nitrogen, such as 5-10-10.

This is likely due to the fact that too much nitrogen, especially early in the season, can cause rapid vegetative growth and produce large plants that fail to produce large tubers.

Always refer to your soil test results to determine whether you should use a balanced formula, like 10-10-10, or one with less nitrogen, like 5-10-10.

Alternatively, you could try making your own homemade potato fertilizer and applying it.

When is the best time to add fertilizer to my potatoes?

Many home gardeners amend the soil early in the spring before planting and apply potato fertilizer at this time. If you choose to use fertilizer at planting time, follow the manufacturer’s recommended application rate unless your soil test results indicate otherwise.

Side-dressing the potatoes when they are 4 to 6 inches tall and ready to be hilled is also standard practice. Repeat the procedure in about two weeks when the potatoes are ready to be hilled again.

Fertilize them once a month until two weeks before harvest.

How should I apply the fertilizer?

How you apply fertilizer varies depending on whether you are using granular fertilizer or a water-soluble fertilizer.

How Do You Apply Granular Fertilizer

  • Broadcasting over the entire gardening area and tilling it into the soil. This method works well if you prefer to work the soil once so that it is ready for planting when you are.
  • Fertilizing individual rows by spreading the appropriate amount in each row and working it in with garden tools. This method works well if you are unsure how many rows you will be planting or if you are growing multiple types of veggies that may require special fertilizers. It also conserves fertilizer as the areas between rows do not need fertilizer.
  • Side-dressing your potatoes before hilling them. Sprinkling fertilizer along the row and working it into the soil before you hill your potatoes ensures your potatoes get the necessary nutrients. You can do this with the first two hillings.

How Do You Apply Water-Soluble Fertilizer

Water soluble fertilizer, like Miracle-Gro, is also a foliar feeder, which means your potato plants can absorb nutrients through their leaves. Water-soluble fertilizers or foliar feeders work quickly and can often show results within a few days.

  • Use a hose-end sprayer to apply water-soluble fertilizer at watering time. Add the appropriate amount of fertilizer to the hose end sprayer’s reservoir and spray the plants with water as you water them. Apply to potatoes about once a month.
  • Mix water-soluble fertilizer with water in a five-gallon bucket and use a bucket or watering can to apply it to your potato plants. This works well if you only have a few plants or if you don’t have access to a hose-end sprayer.

Note: Always read the label carefully. While most water-soluble fertilizers are also foliar feeders, some are not and cannot be applied directly to the foliage.

Can I add too much fertilizer to my potatoes?

Giving your potatoes fertilizer is one of those times when more is not better. Over-fertilizing them can damage your potato plants and inhibit the production of healthy tubers. The most common issue with over-fertilizing potatoes is giving them too much nitrogen. Another problem with applying too much fertilizer is growing massive potatoes with hollow hearts/ centers.

too much fertilizer can result in hollow heart
An oversized potato with a “Hollow heart”

Too much nitrogen results in big, bushy potato plants that look amazing in the garden, but the plant devotes its energy to foliage production and fails to develop large, well-formed tubers. Both the size and number of potatoes will be reduced if you give your potatoes too much nitrogen.

Following the recommended application rate on the container and avoiding fertilizing your potatoes more frequently than once a month is essential to the health of your potato plants.

One pound of 10-10-10 fertilizer (or 2 pounds of 5-10-10) per 100-foot row is commonly recommended, says the Colorado State University Extension.


Potatoes are easy-to-grow in the home garden, but they do need care and attention from the grower from planting until harvest time. By providing them with an abundance of nutrients in the ratio and timings they need, will result in a thriving crop increasing the overall health, yield, and size of your potatoes too.

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