What is the Best Fertilizer for Growing Potatoes? A Buying Guide

Soil fertility is the key component when planting potatoes. It’s the most important factor that affects the yield and the size of your potatoes, as well as their quality. 

If you don’t have good soil, you most likely won’t be able to grow potatoes. Potatoes are known to be heavy feeders, and so you need to make sure that your soil is packed with the necessary nutrients. This is exactly where fertilizers come into play. 

Choosing a suitable fertilizer can be a bit of a hassle, especially if you’re a beginner. So, we created a buyer’s guide to help you choose the best fertilizer for your potato crop. 

In this guide, we discuss everything from soil testing and growth requirements to when and how to apply your fertilizer. 

How to Choose a Fertilizer for Potatoes

The first thing you need to do before planting potatoes is test the soil. Soil testing will give you deep insight into how rich or how poor your soil is so that you can make an optimal decision in terms of fertilizer choice. 

We don’t recommend you skip this step. No matter how good you are at guessing, knowing is much better. 

A decent soil testing kit allows you to test soil acidity as well as nitrogen, phosphorus, and potassium content. We recommend the MySoil Soil Test Kit or the Luster Leaf 1601 Rapitest Test Kit. 

Potatoes – Requirements for Growth

To choose the best fertilizer, you need to understand what your crop needs for growth. 

Soil Acidity and pH Level

Potatoes grow best in loose, well-drained soil. If the soil is too wet, it sticks together and becomes hard for the roots to expand. You need to wait for the soil to dry out a bit. 

Loam and sandy-loam soils are perfect for planting potatoes as they provide good drainage and aeration. However, be careful when planting potatoes in soil that’s overly sandy as it dries too quickly and requires frequent watering. 

The ideal pH level for growing potatoes ranges between 5.2 and 6.5. Avoid planting potatoes in alkaline and saline soil. Alkaline soil increases the risk of the potatoes getting scabs. 

Soil Nutrients

Potato crops demand soil rich in nutrients such as:

• Nitrogen
• Phosphorus 
• Potassium
• Calcium 
• Magnesium
• Sulfur 
• Zinc
• Manganese
• Iron
• Copper
• Boron

All these nutrients have their necessary functions in growing potatoes, but the most important nutrients are potassium, nitrogen, and phosphorus, and this is what we usually focus on when choosing our fertilizer.

Potassium

Potatoes take up high quantities of potassium as it has multiple fundamental functions in growing potatoes. A lack of potassium could affect the crop’s yield, size, and even quality. 

Potassium also plays a major role in the metabolic process as well as reducing disease risk.

Nitrogen

Nitrogen is the most important nutrient when growing potatoes as it significantly affects their growth. You need to ensure suitable amounts of nitrogen to achieve high yields, especially at the first stage of vegetative growth. 

Although, you should also be careful not to add excessive amounts of nitrogen. Excessive nitrogen delays tuber maturity, which, in turn, affects yield. It also negatively affects the crop’s skin conditions.

Since potatoes require well-drained soil, nitrogen management can be hard as it easily leashes through the soil. Therefore, nitrogen fertilizer application is recommended during the growing season. 

Phosphorus 

Phosphorus is important in encouraging early root development and tuber formation. Even with soil that is packed with phosphorus, other factors can lead to phosphorus deficiencies. 

Make sure to use a proper amount of phosphorus during tuber initiation to ensure the formation of the maximum number of tubers. Following this stage, phosphorus is needed to synthesize, transport, and store starch. 

Temperature

To plant potatoes, the soil temperature has to be at least 40°F. To achieve the best yield you can, the soil temperature should range between 60°F to 68°F.

Therefore, potatoes are typically grown in temperate zones in early spring, while in warmer regions, they’re grown in late winter. Although potatoes can tolerate a light frost, it’s recommended to use frost protection. 

Cover Crops

The main job of cover crops is to improve the soil and protect it from erosion and nutrient loss. They do that by returning nutrients to the soil. You can think of them as an alternative to organic fertilizers. 

Cover crops have other advantages, such as smothering weeds and controlling pests and diseases. They’re planted in fields that would otherwise be left bare. 

Examples of cover crops that are used when planting potatoes:

• Legumes, e.g. Soybeans
• Cereals, e.g. Rye
• Grasses
• Crucifers 

Manure and Compost

Manure and compost carry out the same job, which is to cover crops. They act as fertilizers and they help improve the soil before planting potatoes. You can find organic fertilizers made of manure and mixed compost. 

It’s recommended to mix green-based compost and well-rotted manure for best results. Keep in mind, however, that excessive usage of manure, especially those high in nitrogen, can have negative effects on tuber production. 

Fertilizer Use

Now that you’ve tested the soil and understood the requirements for growing potatoes, it’s time to create a fertilizer program. 

We can’t recommend an exact fertilization program as it varies according to the soil and water conditions, your experience, and, of course, your goal yield.

That said, here are a few general tips to take into consideration:

Choose a Suitable Fertilizer

Fertilizers come in different concentrations and ratios. Your goal is to pick a fertilizer that suits your soil.

It’s usually recommended for a home garden or a small field to utilize a fertilizer with a balanced ratio and high concentrations to ensure that the soil gets all the required nutrients. 

However, if you’re using manure and compost before planting, go easy on fertilizers. In this case, you should use a fertilizer with lower concentrations.

The Best Time to Apply Fertilizer 

You should start applying fertilizers about two weeks after planting. In general, potato crops require more nitrogen during the initial two months. 

Some farmers like to use a fertilizer with no phosphorus or potassium at all during those two months. You can do that if your soil is nitrogen deficient and is rich in both potassium and phosphorus. 

If your soil contains enough nitrogen, use a fertilizer with lower concentrations of nitrogen and higher concentration of phosphorus and potassium. 

After the first two months, start using a fertilizer that’s low in nitrogen but high in potassium. If the soil is rich in nitrogen, you can use muriate of potash.

Apply your choice of fertilizer every four weeks unless the instructions on the packaging say otherwise. Stop fertilizing the crop approximately two weeks before harvesting. 

Methods of Applying Fertilizer 

There are several methods for applying fertilizers. Here are some of the easiest methods.

Banding Method

With the banding method, you apply the fertilizer once your potatoes are in the soil. Then, you distribute it all over each row of potatoes. 

Always follow the instructions on the packaging to avoid over-fertilization. It’s better to under-fertilize than to over-fertilize, as the latter can lead to burning roots.

When you reapply the fertilizer when the potatoes are growing, you can apply it in bands along the top or sides of the planted rows. 

The banding method is highly recommended as it’s efficient with both mobile and immobile nutrients. 

Broadcasting Method

This method is when you apply your fertilizer all over the soil’s surface. This is efficient if you’re planting your potatoes in beds.

However, if you’re planting them in a large field, this may not be very efficient as some nutrients aren’t all that mobile, such as phosphorus. Such nutrients are to be applied in bands near roots. 

The Top 5 Potato Fertilizers Reviewed

#1. Voluntary Purchasing Group Muriate of Potash

The Voluntary Purchasing Group Muriate of Potash is our number one choice for the best fertilizer for growing potatoes. This fertilizer is made from muriate of potash, which is just another name for Potassium Chloride. Potassium Chloride is a great fertilizer because of the high potassium content, which is perfect for growing potatoes as well as other root vegetables that need a large amount of potassium to grow, like carrots and squash, among others. It helps with the formulation of vegetative matter as well as root production. It has an NPK composition of 0-0-60, meaning it contains 0% Nitrogen and Phosphorus but a huge 60% Potassium mixture.

This Muriate of Potash from the Voluntary Purchasing Group is a high yield formula, so a single four pound bag will cover 800 square feet of plantable garden soil. The potassium in the fertilizer also aids in producing strong and sturdy stalks on the vegetables, colorful and healthy blooms, as well as growing healthy stems, roots, and tubers. This potash will get your leaves turning green and growing faster, and helps to establish healthy roots systems even in transplants and newly planted bulbs. 

#2. Winchester Gardens Select Organics Potato Granular Fertilizer

The Winchester Gardens Select Organics Potato Granular Fertilizer is another great fertilizer that will ensure your potatoes will thrive in your vegetable plot or garden. This fertilizer has potassium sulfate in it, which is highly effective at delivering potassium to the potatoes, which they need to grow healthy and strong. It has an NPK composition of 6-3-9, meaning it contains 6% Nitrogen (N), 3% Phosphorus (P), and 9% Potassium (K) in its compound, and it includes a spoon and a 3-pound bag upon ordering. 

This Select Organics Potato Fertilizer is great for almost all types of potato, including sweet potatoes, bakers, boilers, and red potatoes, as well as other vegetables with similar properties, such as carrots, onions, or asparagus. It has Potassium Sulfate in its ingredients, which encourages all-around growth and particularly enhances microorganism growth. This all natural and organic fertilizer helps to improve soil quality in addition to keeping your potato plants healthy. 

#3. Down To Earth Acid Mix Fertilizer

Next on our list of best fertilizers for potato growth is the Down To Earth Acid Mix Fertilizer. This fertilizer has a 4-3-6 composition, meaning it contains 4% Nitrogen, 3% Phosphorus, and 6% Potassium in its mixture. In addition to this, it is derived from other natural and beneficial sources, such as Cottonseed Meal, Kelp Meal, Langbeinite, Fish Bone Meal, and Rock Phosphate. The Acid Mix part comes from a 2.5% solution of Humic Acids derived from Leonardite; this is an important compound in humus, which can bind to and help plant roots receive vital nutrients and water.

This fertilizer is perfect to use in early Spring for vegetative growth, and then again when blooms appear in order to encourage lush flowers and fruit, especially those that need a low pH level, such as rhododendrons, azaleas, hydrangeas, evergreen trees & shrubs, blueberries, raspberries, strawberries, and potatoes, among others. A 6 pound box of Down to Earth can cover an area of 120 square feet. 

#4. Jobe’s Organics All Purpose Granular Fertilizer

The Jobe’s Organics All Purpose Granular Fertilizer is a great fertilizer and plant food for potatoes and other plants and vegetables. It contains a 4-4-4 composition – 4% Nitrogen, 4% Phosphorus, and 4% Potassium. You can apply Jobe’s every 2-3 weeks as needed; if planting new vegetables or plants then mix it into the soil before planting, and if you’re adding it to existing trees, plants, and shrubs, then simply feed the established plants at the drip line (the furthest edge of the branch spread). Listed by the USDA for organic gardening, this fertilizer contains no synthetic chemicals, just a fast-acting granular mixture for any and all garden plants and vegetation. 

Jobe’s Organic products come enhanced with their special formula called Jobe’s BioZome. This is a unique and patented blend of healthy bacteria, Mycorrhizal fungi and Archaea, and it increases your garden’s long-term soil quality, promotes plant growth, increases root mass, and additionally helps your garden to resist disease, insects, and drought, as well as other unfavorable conditions. In addition to this, it is renewable, biodegradable, sustainable, and beneficial to the environment. 

#5. Humboldts Secret Golden Tree Additive 

The Humboldts Secret Golden Tree Additive is the final fertilizer on our list of best fertilizers for potato growth. While this is not a fertilizer in itself, it is an additive that, when used in conjunction with a fertilizer, helps to improve soil and foliar nutrient conditions for better crop yields and support conditions for better overall plant establishment, as well as nutrient uptake and abiotic stress tolerance. Containing a potent mixture of kelp, carbs, and minerals, this additive will provide essential nutrients that your plants might not be getting otherwise. 

Humboldts Golden Tree is compatible with many different growing methods, so you don’t need to change your routine when adding it in with hydroponics, aeroponics, coco, DWC, soil, or any other medium. One 16 ounce bottle of this additive can make up to 224 gallons of solution that will last a long time and will continue to feed your plants for years. 

Conclusion

We hope this post was useful in helping you find the best fertilizer for your potato plants. If you’re still a bit on the fence about it, we again recommend the Voluntary Purchasing Group Muriate of Potash because its high concentration of Potassium makes it perfect for potato growth.