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Your Comprehensive Guide on High Potassium Fertilizers 

Guide on High Potassium Fertilizers

High potassium fertilizers help gardeners strengthen their plants when applied properly to the soil. Soils that are rich in potassium will provide the right mix of key elements in promoting overall production.

Potassium is beneficial to your plants by providing them with:

  • Vital ingredients for strong root systems
  • Essential elements to develop abundant flowers
  • Key nutrients to produce healthy fruits, vegetables, and crops
  • Important sustenance to resist diseases

Here are 18 kinds of high potassium fertilizers:

  • Burned Cucumber Skins
  • Sulfate of Potash with Magnesia
  • Dried Banana Peels
  • Comfrey
  • Greensand
  • Kelp
  • Clay
  • Eggshell
  • Wood Ash
  • Granite Dust
  • Soybean Meal
  • Sawdust
  • Alfalfa
  • Bat Guano
  • Wool
  • Compost
  • Manure
  • Coffee and Tea Leaves
What’s the fastest way to add potassium to the soil

Image on istockphoto by Marcus Chung

What’s the fastest way to add potassium to the soil?

Potassium sulfate, commonly known as Sulfate of Potash with Magnesia, is the quickest way to correct potassium imbalance in soils.

What is the best source of potassium for plants?

Burned cucumber skins, sulfate of potash with magnesia, and dried banana peels are some of the fertilizers with high-potassium content.

What is high potassium fertilizer used for?

Normally, fertilizers with high potassium content are applied to encourage abundant flowering and high crop yields.

What is high potassium fertilizer used for

Image on istockphoto by Onfokus

18 options for high potassium fertilizers

Fertilizers that are high in potassium include:

  • Burned Cucumber Skins
  • Sulfate of Potash with Magnesia
  • Dried Banana Peels
  • Comfrey
  • Greensand
  • Kelp
  • Clay
  • Crushed Eggshells
  • Wood Ash
  • Granite Dust
  • Soybean Meal
  • Sawdust
  • Alfalfa
  • Bat Guano
  • Wool
  • Compost
  • Manure
  • Used Coffee Grind and Tea Leaves

Let’s view the fertilizers high in potassium according to their percentage in weight below.

Source% KSpeed
Burned Cucumber Skins272 to 4 weeks
Sulfate of Potash with Magnesia221 to 4 weeks
Dried Banana Peels11.52 to 3 months
Comfrey5.32 to 6 months
Greensand55 years or more
Kelp4 to 134 to 6 months
Clay3.5 to 8.31 to 2 years
Crushed Eggshells3 to 83 to 8 months
Wood Ash3 to 71 to 3 months
Granite Dust310 to 12 months
Soybean Meal2.41 to 2 years
Sawdust2 to 42 to 4 years
Alfalfa22 to 6 months
Bat Guano1.52 to 3 months
Wool1 to 33 to 12 months
Compost1 to 21 to 2 years
Manure0.4 to 31 to 2 months
Used Coffee Grinds and Tea Leaves0.28 to 0.621 to 2 weeks

Now that we know which fertilizers have the highest potassium content, we’ll discuss each one briefly.

Burned Cucumber Skins

Image on istockphoto by gaffera

1. Burned Cucumber Skins

Increase the potassium content in your soil with burned cucumber skins. You can use fresh cucumber skins although they take longer to break down to release the precious nutrients.

How to make your own burned cucumber skins

  1. Turn on your oven to 350 degrees.
  2. While waiting for the oven to warm up, gather the cucumber skins.
  3. Lay the cucumber skins flat on your baking tray.
  4. Place the tray in the oven and take it out after 15 minutes.
  5. Blend or grind the burned cucumber skins into powder.
  6. Sprinkle some on the soil and keep the excess in a container.

You can replenish your soil with potassium every two to four weeks with your homemade burned cucumber skin powder.

Sulfate of Potash with Magnesia

Image on istockphoto by Vitalii Petrushenko

2. Sulfate of Potash with Magnesia

Sulfate of potash with magnesia is known as potassium magnesium sulfate and sometimes as Sul-Po-Mag. It is a specific type of potash that is water-soluble, making it highly ideal as a fertilizer.

It also contains magnesium so you should consider this if you plan to add Epsom salt (epsom salt for tomatoes – row 8) to your garden. You’ll also need to note that sulfate of potash with magnesia is not a balanced fertilizer since it does not contain nitrogen or phosphorus.

Dried Banana Peels

Image on istockphoto by Kyaw_Thiha

3. Dried Banana Peels

Dried banana peels are another natural way to add potassium to your soil. Just like cucumber skins, you can use fresh peels – although dried peels have higher potassium content and release this nutrient faster.

How to make your own dried banana peel fertilizer

  1. Collect as many banana peels as you can.
  2. Dry out the banana peels on a tray and place them in a warm and dry place.
  3. Alternatively, you can place them in a 350-degree oven for 15 minutes.
  4. Allow the peels to turn black, crispy, and crumbly.
  5. Place the peels in a blender and grind them into fine powder.
  6. Sprinkle a few tablespoons around your plants and store the rest safely.

Dried banana peel powder will last for two to three weeks in the soil. Just remember that it has low contents of nitrogen and phosphorus as it is not a balanced fertilizer.


Image on istockphoto by Kerrick

4. Comfrey

Found growing in parts of Asia, North America, and Europe, comfrey provides a relatively high amount of potassium to the soil. Simply add the cut or chopped leaves and mix with your mulch.

Comfrey leaves can last as long as two to six months. It is also rich in nitrogen and phosphorus, although comfrey is mostly used to boost flower and fruit production in plants.

How to make your own liquid comfrey fertilizer

  1. Take several sprigs of large comfrey leaves.
  2. Cut, chop, or shred the leaves.
  3. Place the cut, chopped, or shredded leaves in a large bucket.
  4. Fill the bucket with water.
  5. Cover the bucket for three to six weeks.
  6. The mixture is ready when it has turned into a slurry paste with a strong pungent smell.
  7. Remove and place the decomposing leaves in your compost pile or mulch.
  8. Dilute and apply the liquid solution to the soil as needed.

Image on istockphoto by Inna Dodor

5. Greensand

Greensand is a porous type of sandstone that has large amounts of marine fossils. It has a rich green color and can easily retain water along with minerals.

It can take around five years or more for greensand to completely release its nutrients. This fertilizer is ideal if your soil needs a lot of potassium, some phosphorus, and very little nitrogen.


Image on istockphoto by spiderment

6. Kelp

Kelp is found abundantly in cool shallow underwater forests near the shores of the Pacific coast. These large brown algae are great natural sources of potassium with traces of nitrogen and phosphorus.

This fertilizer releases potassium into the soil for around a period of four to six months. 


Image on istockphoto by victoriya89

7. Clay

Clay traps potassium within its crystals, making it a very good natural fertilizer choice compared to synthetic ones. One such clay is called Illite.

Fertilizers from clay sources can last for one to two years. You have to remember that clay does make your soil more prone to water retention and may cause it to compact over time.

Crushed Eggshells

Image on istockphoto by chengyuzheng

8. Crushed Eggshells

Eggshells are surprisingly high in potassium, even though their main nutrient content is calcium. Crushed eggshells are better than large pieces since they decompose quicker.

If you don’t want to see eggshells in your garden, then add them to your compost. You can also combine finely crushed eggshells with dried banana peel powder.

Wood Ash

Image on istockphoto by NoDerog

9. Wood Ash

The burnt remains of wood can be used as fertilizers for plants. The nutrient content can vary depending on the type of wood that was used.

Wood ash does not contain nitrogen since this nutrient gets burned out upon combustion. This form of fertilizer can be high in alkalinity, so a little goes a long way so that your plant’s root system doesn’t get damaged.

Granite Dust

Image on istockphoto by Emilija Randjelovic

10. Granite Dust

Granite is a form of igneous rock that comes in white, brown, gray, black, pink, or in several color combinations. When crushed to a fine powder, granite can be used as a soil amendment.

It contains a good amount of potassium, along with manganese, magnesium, iron, and calcium. Granite can last for three to five years, slowly releasing potassium into the soil.

Soybean meal

Image on istockphoto by deepspacedave

11. Soybean meal

Once extracted soybeans are dried and ground, the resulting material is soybean meal. This natural form of fertilizer is a great source of potassium and phosphorus but is especially high in nitrogen.

Soybean meal takes one to two years to release its nutrients into the soil. Simply apply on or work into the topsoil and water.


Image on istockphoto by Anele77

12. Sawdust

Leftover dust scrap from lumber mills and woodworking projects make up sawdust. When working with saw dust, always make sure that they are not treated with any unwanted chemicals that might contaminate your soil.

Sawdust can take two to four years to release potassium as well as minute amounts of nitrogen and phosphorus. To improve its nutrient quantity and quality, it is better to add sawdust to your compost first.


Image on istockphoto by Roman Novitskii

13. Alfalfa 

Alfalfa is part of the legume family and can be sometimes referred to as Lucerne. Legumes have good potassium content although they are more known for bringing nitrogen back into the soil through their roots.

It releases its nutrients into the soil for two to six months. Alfalfa can be considered a good fertilizer since it contains all three essential nutrients for plant growth.

Bat Guano

Image on istockphoto by sasimoto

14. Bat Guano

Bat guano comes from the solid excrements of these flying mammals. Since it can be difficult to obtain, bat guano is often collected and sold commercially.

It takes around two to three months for bat guano to release its nutrients into the soil. However, you have to be careful in applying it since it is quite acidic.


Image on istockphoto by Barcin

15. Wool

If you happen to know a farm with excess sheep wool, you’re in luck! Sheep wool can be added to compost to increase potassium content.

Soil amended with composted sheep wool will need only a year or two before being replenished. However, if you’re in a bit of a hurry, you can simply place the wool right under the plants to act as a long-term fertilizer and mulch.


Image on istockphoto by terra24

16. Compost

Decomposed yard waste, kitchen scraps, and other biodegradable materials make up garden compost. Compost also improves the texture of any soil, allowing them to become well-draining while retaining adequate moisture.

Compost can be made at home or sold commercially. It takes a year or two for compost to release its rich nutrients into the soil, making this a highly desirable balanced fertilizer.


Image on istockphoto by alacatr

17. Manure

Farmhouse animals such as horses, cows, pigs, chickens, and rabbits are great sources of manure. It needs to be dried before application to avoid damaging your plants.

Manure takes up to two years to release its nutrients before reapplication.

Used Coffee Grinds and Tea Leaves

Image on istockphoto by eliane

18. Used Coffee Grinds and Tea Leaves

Who knew the remnants of your favorite beverages can be used to fertilize your plants? Granted, these two materials are better suited for plants that require more acidic soil.

You can mix used coffee grinds and tea leaves directly into the soil, which will be most effective for a week or two. If you have more time to spare, add both materials as ingredients to your compost as long as both are from organic sources.

That’s it! Did we miss any great high potassium fertilizers that should be on this list? Drop your suggestions in the comment box below to let us know!

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