15 Fertilizers High in Potassium: The Ultimate List


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Potassium is one of the three base nutrients used in all fertilizers. It’s an essential nutrient for plant health and growth, as plants use potassium to absorb nitrogen from the ground and produce proteins. High potassium fertilizers enhance crop yields. 

Here is a list of some of the best fertilizers that are high in potassium:

  1. Manure and composted manure
  2. Wood ash
  3. Kelp meal
  4. Greensand 
  5. Granite dust
  6. Comfrey
  7. Banana peels and eggshells
  8. Wool potting compost
  9. Coffee grounds and tea leaves
  10. Organic solution grade potassium sulfate 
  11. Muriate of potash granules 
  12. Alfalfa pellets
  13. Cottonseed meal
  14. Soybean meal
  15. Cucumber skin ash

In this article, I’ll explore each of these fertilizers in more detail and their advantages when used as a fertilizer. 

FertilizerPercentage of Potassium
Manure and Composted Manure2
Wood Ash3 – 8
Kelp Meal5
Greensand3
Granite Dust1-5
Comfrey5.3
Banana Peels and Eggshells5 – 8
Wool Potting Compost1 – 3
Coffee Grounds and Tea Leaves0.28 – 0.62
Organic Solution Grade Potassium Sulfate by Down to Earth50
Muriate of Potash Granules by Easy Peasy All Natural60
Alfalfa Pellets1.8 – 2.9
Cottonseed Meal1.5 – 2
Soybean Meal1 – 2
Cucumber Skin Ash27.2

1. Manure and Composted Manure

When potassium levels are low in the soil, the usual culprit is a low level of organic matter in the soil. Organic matter is rich in all three nutrients needed by plants, i.e., nitrogen, phosphorus, and potassium. Manure and composted manure are excellent sources of potassium for plants. 

When manure is added to the potting soil or growing land in a ratio that meets the plants’ nitrogen requirements, the amount of potassium will exceed the plant’s requirements

2. Wood Ash

Wood ash refers to the powdery remains of wood after it has been burnt for kindling. It’s a traditional source of potassium for plants used in plant rearing and agriculture for a long time. 

Wood ash is also water-soluble, making it excellent for use in gardens and agriculture. Being water-soluble means it can work quickly to raise the pH and potassium levels of the soil. 

In one study conducted on the cocoa plantations of Indonesia, wood ash was as good as commonly used commercial potassium fertilizers. 

When using wood ash or other plant-burning residues, it’s important to be careful about the kind of ash you use. Don’t use ash from coal, pressurized wood, cardboard, or treated wood as they can have additives harmful to your plants. 

Instead, use a good quality hardwood ash like the Premium Double Sifted Hardwood Ash from Mr. Dirt Farmer that you can buy on Amazon.com or directly from mrdirtfarmer.com, which is clear of any debris or waste.

3. Kelp Meal

Kelp or seaweed has been used as a fertilizer for thousands of years. It supplies the necessary macronutrients of nitrogen, phosphorus, and potassium to the plants while enriching soil quality. 

You can apply kelp meal to plants in several different ways. You can mix it with the potting soil, but most farmers and gardeners prefer water-soluble versions. 

Another option for supplying kelp to plants is using a kelp-based fertilizer like the Organic Kelp Fertilizer Supplement by Bloom City, available on Amazon.com or the Maxicrop Kelp Meal available von arbico-organics.com. This concentrated fertilizer comes in a 32 oz (907 g) bottle that can make about 180 gallons (681 liters) of fertilizer when diluted. It works well and doesn’t have a strong smell, unlike other kelp-based fertilizers. 

4. Greensand 

Greensand is sediment from the sea also found as rocks. Greensand has been used as fertilizer for crops and plants since long before the Civil War. It’s a slow-release fertilizer also known as glauconite. 

The advantage of greensand is that too much greensand won’t harm the plant, unlike most other fertilizers. Your plants will simply absorb as much potassium as they need, and the rest of the greensand will remain in the soil, keeping it aerated. 

One of the best ways to use greensand is as a soil conditioner. Add a greensand powder to the soil in winter to recharge it and prepare it for planting and replanting in the spring. This product is a fine powder that can easily be mixed with potting soil and is excellent value for money. 

5. Granite Dust

Granite dust or granite slurry is a valuable byproduct of granite manufacturing highly valued in the agricultural and commercial gardening industries as a fertilizer. 

Granite dust is rich in macro and micronutrients, including potassium, calcium, and aluminum, necessary for crop and plant growth.

Some percentage of the potassium in granite dust is immediately available to plants since granite dust is water-soluble. The remaining potassium seeps into the soil over time, improving its overall quality. 

Granite dust also can neutralize acidic soils, which is important to remember before using it as fertilizer. It’s an excellent addition to the potting soils of crops and plants that prefer more alkaline soils. 

6. Comfrey

Comfrey is a perennial shrub that grows in North America, Europe, and South Asia. It’s known as a dynamic accumulator for its capacity to accumulate nutrients and improve the quality of the soil. 

The plant can be used in many ways. Simply planting comfrey helps the overall quality of topsoil, with nutrient levels increasing about 47% – 232% over time. You can grow the plant from seeds like True Comfrey by Earthcare Seeds (You can find all product recommendations at the end of the article). These seeds are heirloom comfrey and GMO-free. 

The best way to use comfrey as a fertilizer is by incorporating freshly cut leaves of the plant in mulch. The mulch can be made up entirely of the comfrey leaves as well. 

Liquid fertilizer can be made by steeping the shredded leaves in the water in a covered container for about 3 to 6 weeks. The resulting fertilizer has a strong smell but can be used directly on the plants as needed. 

The leaves supply all the macronutrients to the soil, not just potassium. However, the high potassium levels make comfrey an excellent fertilizer for plants like tomatoes, potatoes, peppers, and cucumbers.  

7. Banana Peels and Eggshells

The banana fruit is known for being high in potassium, but the peels are also rich in potassium. There’s about 78.10 mg of potassium per gram of banana peel, approximately 0.0027 ounces per 0.002 pounds of banana peel. 

Eggshells are also a good source of potassium for plants, though the primary nutrient that plants derive from eggshells is calcium. 

One of the easiest ways of using banana peels and eggshells as fertilizer is by adding them to compost. 

Fresh banana peels have a lower potassium level than dried banana peels, so if for plants that need an extra boost of potassium, a better option would be to dry the banana peels in an oven and powder them in a blender or a spice grinder. This powder can then be added to your plant beds or potting soil. 

The banana peels and egg shells can be placed into a covered container with water to make liquid fertilizer. The peels will decompose and release the potassium into the water. However, it will smell, so the container is best placed outside and used quickly. 

8. Wool Potting Compost

The use of sheep’s wool in compost has several benefits for the soil. It aerates the soil, prevents runoff of nutrients, and is a great slow-release fertilizer with high levels of nitrogen and potassium. 

You can use Wool as mulch to stop nutrient runoff. It has been used for this purpose since the 1900s. The absorbent nature of wool makes it hold on to water and fertilizers, preventing them from running off. To use wool as mulch, you should place it right underneath the plants. 

While wool is biodegradable, it does take a long time. Wool decomposes over three months to two years but is rich in nitrogen and potassium.

Composted wool is a great source of nutrients for plants, but raw wool can just as easily be added to the soil in the winter to prepare the soil beds for the next planting season. 

9. Coffee Grounds and Tea Leaves

Coffee ground and tea leaves are great for adding much-needed nutrients to the soil. Both coffee grounds and tea leaves are rich in nitrogen, phosphorus, and potassium, and dried grounds are richer in these nutrients than fresh grounds. 

By far, the best way to use coffee grounds and tea leaves as fertilizers is to compost them. They can be added to composting mixtures, but ensure that the compost volume of coffee grounds and tea leaves is about 20-35%. If this value is higher than 35%, it can prevent the compost from breaking down. 

The composted coffee grounds and tea leaves have a neutral pH, and they can then be used for all plants, not just the plants that can tolerate acidic soils. 

Coffee grounds and tea leaves can also be used as liquid fertilizers by steeping used grounds and tea leaves in water. The subsequent weak coffee or tea can then be used as fertilizers for plants. 

The best way to apply used grounds is by working them into the soil. Remember not to use too much in the same pot – about a spoonful is sufficient. Any more, and the grounds and leaves can prevent water retention. 

They shouldn’t be left on top of the soil to decompose because it will encourage the growth of fungus, which could harm the plant. 

10. Organic Solution Grade Potassium Sulfate 

Potassium sulfate is one of the main potassium-based fertilizers used in agriculture and gardening. It’s more expensive than the commonly used potassium muriate but is effective for improving the quality of yield in garden plants like tomatoes. 

Potassium sulfate tends to be more effective than muriate as potassium sulfate also introduces sulfur in the potting soil, which is necessary for plant growth and yields. 

Using organic potassium sulfate like the Organic Solution Grade Potassium Sulfate by Down to Earth ensures that farming practices don’t harm the environment. The potassium sulfate from Down to Earth is listed by the Organic Materials Review Institute and is designed to be easy for plants to absorb. 

This fertilizer is effective for addressing concerns of potassium deficiencies in plants immediately. 

11. Muriate of Potash Granules

Muriate of potash or potassium chloride is the most easily available and commonly used potassium-based fertilizers. It’s typically available in granule form and mined from rock deposits. 

Muriate of potash has a higher percentage of total potassium than other fertilizers since it’s a straight potassium fertilizer. It’s also cheaper than other compound fertilizers. However, applying muriate in large quantities can result in salt-based damage to plants, especially seeds and young plants. 

A good Product is the Muriate of Potash Granules by Easy Peasy All Natural. This brand of muriate of potash is an organic source of potassium chloride for plants, known for being easy to use and effective, with the majority of gardeners noticing a significant improvement in the size of the yield. An alternative would be Potassium Chloride (Muriate of Potash) 0-0-62 from Greenway Biotech, Inc. You can find all product recommendations at the end of the article.

12. Alfalfa Pellets

Alfalfa is a plant that needs a lot of potassium to grow. As a result, the plant itself contains high levels of potassium. 

Alfalfa pellets are typically used as animal feed, but their use in gardens as a green fertilizer has been growing over the years. The pellets can’t be used directly on the soil as they won’t break down quickly enough to be absorbed in the soil. 

The pellets need to be crushed then composted before they can be used as fertilizer. It’s well worth the effort to compost the alfalfa as the pellets contain all the necessary macro and micronutrients for plant growth and improve the soil quality. 

The best way to make an alfalfa fertilizer is to use 100% dry pellets like the Walt’s Organic Alfalfa Pellets, which are sun-cured without any additives. The other ingredients include a little bit of sugar and water. The mixture should be covered and insulated so that the heat can speed up the process of decay and breakdown. With insulation, the fertilizer will be ready for use in two days. 

13. Cottonseed Meal

Cottonseed meal is the byproduct of processing cotton. Sometimes it’s used as feed for cattle, but one of the most effective uses of this byproduct is fertilizer. 

While cottonseed meal is typically known for its high nitrogen content, it does have a lot of potassium and is an effective source of potassium for plants. 

When using cottonseed meal, it’s important to ensure that the meal is from organic sources. Non-organic cottonseed meal will be full of pesticides used in cotton production, which could be harmful when used as a fertilizer.  

One of the primary advantages of cottonseed meal as fertilizer is that it doesn’t burn plants even when used in excess. It’s easy to use and most effective as a slow-release fertilizer. 

14. Soybean Meal

Soybean meal is similar to alfalfa, with the added advantage of being easier to use. The meal is usually finely milled with a powdery texture. When used as a fertilizer, it can be directly sprinkled onto the soil to be effective. 

Soybean meal must be used carefully because it can burn plants if used in excess. Ideally, the meal should be sprinkled or mixed into the soil a few weeks before planting to give it time to break down and release nutrients into the soil. This will protect seeds and seedlings from fertilizer burn. 

15. Cucumber Skin Ash

Like wood ash, cucumber skins can be burned to produce ashes that are a rich source of potassium for your garden. 

While these are not an easily available ingredient and not viable for large-scale use, they’re useful for home gardens. Cucumber skins are rich in phosphorus and potassium, and the quantity of these nutrients increases when they’re dried out or burned into ashes, much like other peels and fruit cast-offs like banana peels. 

The ashes can be mixed in with potting soil or diluted with water for a fast-release source of potassium. 

FAQs

Is Potash the Same As Potassium?

Potash is a potassium mixture with trace minerals and chemicals. Potash typically refers to potassium chloride, a salt that is used as a fertilizer and sold as muriate of potash.

How Do You Fix Too Much Potassium in the Soil?

Soil that has too much potassium will burn plants, especially seedlings or seeds and will need to be changed up or flushed out with water. The soil must be flushed then allowed to dry completely, and this process should be repeated a few times to ensure that all the excess potassium has run off. 

Is Clay Soil High in Potassium?

Some varieties of clay like illitie are rich in potassium. However, clay soils are thick and sticky, forming pockets for potassium to hide out of reach from the plants. This makes potassium uptake from clay soils difficult for plants. 

Clay soils also tend to have a high capacity for water retention, which further dilutes the potassium in the soils and makes it difficult for plants to absorb any of the available potassium. 

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Lars

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