High Potassium Fertilizer

Just as humans need a balanced diet with all the essential nutrients to live a healthy life, gardens also require the right balance of nutrients to stay healthy. The role of potassium in plant health and growth is extremely important.

It has several functions, including regulating enzymatic processes required for growth, regulating water use, and providing plants with the potential to withstand extreme temperatures, pests, and drought.

Overall, plants need potassium for vigorous growth, disease resistance, winter survival, and forage quality. To supply your plants with an adequate quantity of potassium, you need to often use a high-potassium fertilizer.

Well, the good news is that several natural high-potassium fertilizers are easily available. In this article, I’ve covered the most important high-potassium fertilizers, both natural and synthetic. Let’s get started.

potassium plays a vital role in manure

Table of Contents

High Potassium Fertilizers

Before getting into the details, let me first tell you how to find out if your plants need potassium. Plants that lack potassium typically develop the following symptoms:

  • Floppy leaves
  • Weak stems
  • Discoloured leaves with yellow or brown tips; or leaves may appear burnt along the edges

If you come across such symptoms, you should consider applying a high-potassium fertilizer to your plants and soil. Now, let’s take a look at some of the best high-potassium fertilizers combined with information about the potassium percentage in each one of them, their nutrient release speed, and how effective they are.

potassium sulfate

1. Kelp meal

Kelp meal is an excellent source of potassium. The potassium levels in it are around 4% by weight, but depending on the process, blend, and brand, they can get up to almost 13%. You should certainly read the label when buying kelp meal, as some kelp products focus more on plant hormones or micronutrients and have very little potassium.

Plant hormones are one of the best features of kelp. Choose to buy a kelp product with plant hormones and a decent level of potassium. Plant hormones promote strong root growth and facilitate the overall bright new growth of your plants.


Greensand is green-coloured sand or sandstone found on the ocean floor. It is mined to be used as a fertilizer or soil conditioner. Also called glauconite, greensand is a slow-release fertilizer.

The greatest advantage of greensand is that even if you apply too much of it to your plants, it won’t harm the plant. Plants will absorb as much potassium as they require, and the remaining greensand will just remain in the soil. It will probably keep the soil aerated.

Greensand has 3% potassium by weight. The best way to use it is as a soil conditioner. You can add greensand powder to the soil in your garden during the winter to recharge it. This way, you can prepare the soil for springtime planting and replanting.

3. Banana peels and eggshells

Most of us know that bananas are rich in potassium, but not many of us are aware that dried banana peels are 42% potassium! Eggshells are also a great source of potassium, though calcium is the principal nutrient plants derive from them.

The best way to use banana peels and eggshells as high potassium fertilizer is by adding these to compost.

Remember that dried banana peels have a higher potassium level than fresh banana peels. So, if your plants need a boost of potassium, you should dry the banana peels and powder them. You can add the powder to your potting soil or plant beds.

balanced fertilizer from banana peel

4. Cucumber skin ash

The ash of cucumber skin is not the first thing that comes to mind when speaking of fertilizers! But, trust me, it is an excellent, organic source of potassium for your plants. It contains a lot of potassium–perhaps more than you realize.

The ash of cucumber skin contains 27% potassium by weight. Burned cucumber skins serve as fast-release fertilizer; in other words, the nutrients become available as soon as they decompose.

Burned cucumber skins contain 11% phosphorus by weight, but they don’t contain any nitrogen. Well, if you don’t wish to burn your cucumber skins, you can opt to add them to the compost pile. It will give your garden plants an extra boost.

5. Clay (Illite)

Illite, the most common clay material, is a fertilizer containing 3.5% to 8.3% potassium. While you cannot compare it to cucumber skin ash or other natural high potassium fertilizer, it remains a good choice if you’ve got to add some amount of potassium to your garden soil.

Studies suggest that potassium gets trapped within Illite, but this clay material is unavailable at first, eventually making it a slow-release fertilizer. Clay is a great option for organic gardeners who hate using artificially created chemical fertilizers.

6. Granite dust

An igneous rock by nature, granite is normally pink, white, grey, or a mixture of these colours. Granite dust is created by crushing granite to form dust. You can use it as a soil additive if you want to supplement nutrients for your plants.

Granite dust contains 3% to 6% potassium by weight. Besides, it contains small quantities of iron, calcium, magnesium, and manganese. Granite dust is a slow-release fertilizer and remains effective for three to five years or longer. The only downside of granite dust as fertilizer is that it does not contain nitrogen. 

too much potassium and granite dust

7. Compost

Compost is a brilliant, all-round source of potassium as well as other nutrients required for the overall growth of your garden plants. If your plants need more potassium, add vegetable scraps rich in potassium–especially banana peels, potato peels, and bits of cucumber– along with manures, sawdust, and a dose of wood ash. You can easily custom-blend compost based on your needs, right in your backyard.

8. Bat guano

Bat droppings, or bat guano, make excellent high-potassium fertilizer. The raw form is extremely rich in potassium, nitrogen, and phosphorus, as well as a wide range of various micronutrients and trace minerals. Perhaps, soil microbes are fond of the stuff, ultimately making it an amazing way to boost the overall health of your garden plants.

While it’s not easy to source bat guano from the bat itself, thankfully, there are many different commercial varieties available in stores. Just make sure you check the label and buy the one that has more potassium content.

9. Alfalfa pellets

Alfalfa contains extremely high levels of potassium. You can buy alfalfa pellets from any of your local stores. These pellets are generally used as animal feed; however, their use for plants as a natural fertilizer has been growing rapidly.

You should not use the alfalfa pellets directly on the soil, because they won’t break down fast. You need to crush the pellets and then compost them before using them as a fertilizer.

soil ph helped by Alfalfa pellets

10. Soybean meal

Soybean meal is almost similar to alfalfa, but it’s easier to use. The meal is generally finely milled to form a powdery texture. When you use it as a fertilizer, you should directly sprinkle it onto the soil for maximum effectiveness.

You need to be cautious when using soybean meal, because if used in excess, it can burn your plants. It should be ideally sprinkled or mixed in the soil several weeks before planting so that it has time to break down and gradually release its nutrients into the soil. This way, you can protect the seeds and seedlings from getting burned by the fertilizer.

11. Cottonseed meal

Cottonseed meal is extracted as a by-product of processing cotton. Cottonseed meal is normally known for its rich nitrogen content, but it also has a lot of potassium.

When you opt to use cottonseed meal as a potassium supplement, make sure that you’ve sourced it from organic resources. Non-organic cottonseed meal is available in stores, it will have a high pesticide content, which could harm your plants.

One of the greatest reasons you should use cottonseed meal as a high-potassium fertilizer is that even if you use it in excess, it doesn’t burn your plants. It is easy to use and amazing as a slow-release fertilizer.

12. Manure

Manure is the most preferred fertilizer by organic farmers and gardeners across the world. It is filled with the three main nutrients, and contains 0.5 to 1.9% potassium by weight, depending on the kind of manure chosen.

Of all kinds of manure, poultry litter is the most beneficial– well, that’s the sawdust that you use as bedding for turkeys and chickens, which absorbs their waste. The good news is that the potassium present in manure is in a form that is accessible to plants.

soil test before adding manure

13. Potash

Potash is popularly known as the old farmer’s friend. It is a reliable source of potassium. As a fertilizer, potash comes in several different forms and contains different nutrient loads. The most common one is potassium chloride or muriate of potash, which has an NPK ratio of 0-0-60! It is extremely powerful, and with very little material, you can cover a vast area.

Another commonly used potash is sulphate of potash magnesia. It is a compound that contains a large quantity of magnesium and sulphur besides potassium. Its NPK ratio is 0-0-21. If you want quick results in your garden, you can use these chemical fertilizers that are extremely high in potassium content.


I’m sure I’ve covered all the important and easily available high-potassium fertilizers for your plants. Let me do a quick recap of the important points.

  • Before you use a high-potassium fertilizer on your plants, make sure they are showing signs of potassium deficiency, including floppy and discoloured leaves and weak stems.
  • There are many naturally available organic potassium fertilizers, including manure, compost, cucumber skin ash, banana peels, and eggshells. These can be easily made in your backyard.
  • If you want fast-acting potassium supplements and you don’t mind buying store-bought fertilizers, you can go with potash, kelp meal, bat guano, greensand, and cottonseed meal.
  • Make sure you choose a high-potassium fertilizer depending on the needs of your plant and soil and whether you want a fast-release or slow-release fertilizer.
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Oliver Wright
Oliver Wright

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