Organic Potassium Sources and Application Methods

Hello fellow cultivators!

This month we’re focussing on Potassium (K). First we dove into the role it plays in growth and flower development, and then we discussed the issues that can come with excessive and deficient Potassium levels. In this article we want to focus on how organic growers can ensure they are maintaining the correct potassium level in their plants. 

As we’ve discussed previously, Potassium (K) plays a pivotal role in the health and productivity of cannabis plants, influencing water uptake, enzyme activation, and the synthesis of proteins and starches. For organic growers, managing potassium levels using natural sources is key to promoting robust plant health and optimal yields. Here’s a guide to some effective organic potassium sources and tips on how to apply them when your plants exhibit potassium imbalances.

Common Organic Sources of Potassium

Wood Ashes:

  • Wood ash is an excellent source of potassium for organic growers. It’s derived from burnt hardwood and can contain up to 10% potassium. Additionally, wood ash has liming effects, which can help neutralize acidic soils.

Kelp Meal:

  • Kelp meal is made from dried oceanic seaweed and is not only rich in potassium but also contains a plethora of micronutrients beneficial for plant growth. It’s a slow-release source of potassium, making it gentle and effective over time. Soluble kelp is a clean and effective organic source of potassium that mitigates the sodium and heavy metals seen with typical kelp meal.


  • Well-balanced compost can provide a good amount of potassium, especially if made with banana peels, orange rinds, and other fruit wastes that are high in potassium.


  • Greensand is a mineral derived from ancient oceanic deposits. It contains a form of potassium silicate that provides a slow release of nutrients, which is beneficial for maintaining soil health and ensuring a steady supply of potassium.

Sul-Po-Mag (also known as langbeinite):

  • A naturally occurring mineral compound that provides not only potassium but also sulfur and magnesium. This source is excellent for providing multiple nutrients and is especially useful if soil tests indicate deficiencies in any of these areas.

Expert Insights

Now that we’ve taken a look at some common organic sources of potassium we wanted to spend some time discussing some pros and cons of the different sources and things to look out for. For that we got in touch with Daniel Fink from Vital Garden Supply in Nevada County, CA. Daniel’s experience as an organic cultivator and with Vital Garden Supply gives him valuable insights into selecting organic potassium sources for cannabis cultivation. 

According to Daniel, while wood ash and kelp meals are commonly suggested for its potassium content, it’s important to be cautious as it can be high in sodium and other undesirable elements. Soluble kelp provides a clean, effective, and more desirable organic source. Similarly, greensand, although a traditional source, may contain heavy metals that could be harmful. He recommends more sustainable and cleaner alternatives such as coco blends, which are rich in potash and offer a balanced potassium source. 

Additionally, Daniel points out that homemade compost, especially those enriched with hemp stalk and squash waste, can have significantly higher potash levels. However, he cautions against certain manure-based composts, which might contain excessive potash due to the wood ash used in animal stalls. 

These insights underscore the importance of choosing the right potassium source and testing fertilizers like manure and compost to ensure healthy plant growth and sustainable cultivation practices.

Application Methods for Addressing Potassium Imbalances

Identifying Potassium Needs:

First, it’s important to accurately assess the potassium levels in your leaf tissue and soil through testing. This is the most accurate way to objectively determine the nutrient levels inside your plants and the soil they are growing in.

For Deficient Plants:

  • Direct Soil Amendment: Mix any of the above potassium sources directly into the soil around the base of the plants. For example, wood ashes can be sprinkled lightly around the plant but should not come into direct contact with the stems or leaves due to its alkaline nature.
  • Top Dressing: Apply kelp meal or compost as a top dressing, gently working it into the top layer of soil. This method helps avoid disturbing the root system and provides nutrients closer to where they are absorbed by the plant roots.
  • Liquid Feeds: Create a liquid feed by steeping compost or kelp meal in water to make a compost tea, which can then be used to water plants. This provides a quicker boost of potassium if plants are showing acute deficiency symptoms.
  • Foliar Application: Soluble potassium sources, such as potassium sulfate or liquid kelp extract, are ideal for foliar sprays and soil drenches due to their easy solubility in water. Foliar applications involve spraying a diluted solution of nutrients directly onto the leaves of the plant, allowing for rapid absorption through the leaf surface. This method can be particularly effective for correcting nutrient deficiencies quickly, as it bypasses the soil and delivers nutrients directly where they’re most needed.

For Excessive Potassium:

  • Adjusting Fertilization Practices: If potassium levels are high, reduce or eliminate potassium additions, focusing instead on balancing other nutrients, particularly nitrogen and magnesium, which can be blocked by high potassium levels.
  • Improving Soil Biology: Enhance soil health through the addition of compost and other organic matter that boosts the biological activity in the soil. This can help improve the nutrient balance and availability.

General Tips:

  • Regular Monitoring: Regularly perform leaf tissue analysis to monitor nutrient imbalances and adjust your fertilization regimen accordingly.
  • pH Management: Ensure the soil pH is optimal for cannabis cultivation (typically between 6.0 and 7.0), as pH levels can significantly affect nutrient availability.

Using these organic sources and thoughtful application methods, organic growers can effectively manage potassium levels, leading to healthier plants and more bountiful harvests. Remember, the key to nutrient management is proper nutrient monitoring, ensuring that all nutrients are available in harmony.

Nutrient Monitoring through Leaf Tissue Analysis

Close monitoring of the nutrient levels in your plants is the only way to be sure that your plants are receiving the right amount of key nutrients, such as potassium. Ready to start using leaf tissue and soil analysis to level up your cultivation? We offer all new clients a free round of testing as a way to demonstrate the power of this information. 

Contact us today at 707-398-8346 or email to schedule your free first round of testing!

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