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NPK For Potatoes – Whats The Best Ratio?

Potatoes are a rewarding crop to grow; however, they come with challenges that may surprise an unseasoned gardener. Potato plants must grow in full sun and loose, sand-like soil for ideal potato production. If soil is clumpy or clay-like, potato plants may not produce full-sized potatoes. If potato plants lack full sun, some nutrients can support their growing process and overcome the light deficiency. NPK fertilizer is made up of nitrogen (N), phosphorus (P), and potassium (K), and there are many organic varieties available that support plant and vegetable growth. What many gardeners want to know is if NPK is good for potatoes?  

Yes, organic NPK fertilizers support the health, growth, and harvest of potatoes. Exploring different ratio options is key to ensuring you provide the right amount of nutrients for the type of potato and its different growing phases. The pre-existing nutrients in one’s soil also play a role in choosing the best NPK ratio that will best support your potato crop.  

Read on to learn more about NPK, other nutrient sources, and care for potatoes.

Benefits Of NPK For Potatoes

The three macronutrients most beneficial to potatoes and many other plants’ development are nitrogen, phosphorus, and potassium, NPK. They are called macronutrients because they are distributed to plants in higher doses than micronutrients, which also help to ensure optimum plant health and harvest. The recommended dosage will vary depending on the plant and its growing phase. We’ll dig into this further, in regards to potatoes, later in the article.  

MacronutrientBenefits
Nitrogen (N)Nitrogen is beneficial to the potato plant in different ways throughout its life. As a seedling, it supports healthy root, vine, and leaf growth.  As a mature plant, nitrogen aids the potato through healthy root, tuber, and vegetable growth.  
Phosphorus (P)Phosphorus is helpful to the plant’s root and tuber growth throughout a potato’s life. It is especially essential to early growth and maintaining growth and health during potato production.  
Potassium (K)Potassium is supportive to potato plants throughout their growing phases as it aids in the transport of water and nutrients. It is ideal for the plant to have larger quantities of potassium as it matures and begins producing potatoes.  

Best Practices Of Using NPK For Potatoes

If using an NPK fertilizer for potatoes, it’s valuable to know appropriate ratios for the phases of the plant’s life from seedling to producer. It is also crucial to test the soil the potatoes will grow in for pre-existing nutrients and deficiencies. If, for instance, your soil is already high in nitrogen, you might reduce the amount of nitrogen in the recommended NPK ratio for your potato plants.  

The NPK ratio is a simple formula that calculates the quantities of nitrogen (N), phosphorus (P), potassium (K), and water, which is used to dilute the mixture. So a 14-7-21 NPK mixture combines 14 parts nitrogen to 7 parts phosphorus to 21 parts potassium and 44% diluted in water. There are many organic NPK fertilizer options on the market with different ratios to suit the needs of a plant throughout its different stages of growth.  

From seedlings through early growth, potato plants need high nitrogen levels to support rapid root and leaf development. An NPK ratio of 34-0-0 is ideal for supporting the growth of the potato plant in this early phase of life. After about two months, it’s important to adjust the NPK ratio and use a fertilizer that is higher in potassium to enhance the growth of its roots and tubers.   

Phosphorus is beneficial to the potato plant in fairly consistent quantities throughout its life. Typically potatoes thrive with lower levels of phosphorus to potassium and equal or lower nitrogen levels. For the last weeks before harvest, an NPK ratio of 14-7-21 will most likely lead to an abundance of potatoes from your crop.  

Beneficial Micronutrients

Several micronutrients aid in maintaining a healthy potato crop. Sometimes gardeners will find these micronutrients pre-existing in the soil after conducting a soil test. If the soil lacks these micronutrients, you can purchase soil additives to supplement the soil and support continued plant health.  

MicronutrientBenefits
MagnesiumMagnesium supports the energy transfer during the photosynthesis process. It is essential in distributing food energy throughout the potato plant.  
Iron Iron is also supportive of the potato plant’s photosynthesis. Often, crops that have been flooded or are in highly alkaline soil may show signs of iron deficiency. Without these adverse conditions iron is often pre-existing in the soil in addition to the plant producing it independently.
CalciumCalcium helps to protect potatoes from disease and supports the overall strength of the potato plant. Positive calcium levels are essential to plant health, especially during extreme temperature conditions such as heat or drought.     
BoronBoron supports the potato plant’s metabolism and energy transports. It commonly exists in soil and may not need to be supplemented.  
ZincZinc aids the potato plant in metabolizing nitrogen. It distributes that energy throughout the plant, enhancing its overall health.  
ManganeseManganese supports the photosynthesis process of the potato plant.  It helps to metabolize nutrients and transfer energy throughout the plant.  

Providing Nutrients For Differing Potato Types

All varieties of potatoes fall into one of two categories: determinate or indeterminate. If you recognize these terms from studying and growing tomatoes, please know that they are defined differently from potatoes.

Determinate potatoes produce more tubers in a single layer below the soil, and they also reach harvest more quickly than indeterminate varieties. Indeterminate potatoes grow more slowly but produce tubers in multiple layers along the stem. This can result in a more bountiful harvest than determinate potato types if grown in a tiered manner through hilling or in potato bags.  

Determinate and indeterminate potato varieties do not require too much variation in nutrients. The biggest concern to address when fertilizing these differing types is that indeterminate varieties will be producing tubers throughout a longer growing season than determinate types.

Because of this, using more consistent supplements of phosphorus throughout the potato plant’s life cycle will help to support the long-term tuber growth that indeterminate types need.  

Final Tips For Caring For Potatoes

Because it is of the utmost importance for the potatoes of a potato plant to thrive beneath the earth, gardeners must never forget to test and address soil conditions before anything else when planning for a potato crop.

Soil may need to be augmented with sand or other loose, organic materials to allow for ease in plant effort as the potato grows. Soil may be high or low in macro or micronutrients and need fertilizer adjustments. Once this information is determined, using the knowledge shared in this article to properly provide nutrients to your potato plants should lead to healthy plants and a bountiful harvest.