Fertilizer programs should always be tailored to specific crops, growing conditions, and end-use environments. For guidance on controlled-release fertilizers, product selection, or application strategies, contact one of our authorized Plant-Prod distributors for local support and recommendations.

Fertilizer programs should always be tailored to specific crops, growing conditions, and end-use environments. For guidance on controlled-release fertilizers, product selection, or application strategies, contact one of our authorized Plant-Prod distributors for local support and recommendations.

What Are Chelated Micronutrients?

Chelated micronutrients consist of a micronutrient ion bound to an organic molecule known as a chelator. This chelating agent surrounds the micronutrient in a stable structure that protects it from reacting with other ions in the growing medium or nutrient solution.

This protection prevents micronutrients from precipitating, oxidizing, or becoming immobilized — reactions that can occur when micronutrients are supplied in non-chelated forms. Chelation improves the stability and plant availability of micronutrients such as iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu).

Why Chelated Micronutrients Are More Available Than Sulphates

Sulphate micronutrients dissolve in water but exist as free metal ions once in solution. These ions can readily react with phosphates, carbonates, or hydroxides, forming insoluble compounds that plants cannot absorb. These reactions occur more frequently as pH increases, particularly above pH 6.0–6.5.

Chelated micronutrients remain protected from these reactions. The chelating agent keeps the micronutrient soluble and available across a wider pH range maintaining consistent nutrient availability.

Sulphates vs. Chelates: Key Differences

Iron: The Most Commonly Chelated Micronutrient

Iron is the micronutrient most frequently supplied in chelated form because it is highly sensitive to pH and oxidation. As pH increases, iron readily converts into forms that are poorly available to plants, leading to deficiency symptoms even when total iron levels appear sufficient.

Chelated iron protects iron from oxidation and precipitation, making it beneficial for greenhouse, hydroponic, and high-pH growing systems.

Choosing the Right Iron Chelate Based on pH

Not all iron chelates perform equally. Chelate stability — and therefore iron availability — is strongly influenced by root-zone pH.

As pH increases, iron availability from weaker chelates declines, increasing the risk of deficiency if chelate selection is not adjusted.

Compatibility Risks When Mixing Sulphates and Chelates

Using sulphate micronutrients alongside chelated micronutrients can introduce compatibility challenges. Metal ions from sulphates — particularly copper, zinc, and manganese — can displace iron from its chelate. When this occurs, iron may precipitate and become unavailable to plants.

Depending on pH and solution conditions, this exchange can result in iron losses of 20–50%, increasing the risk of iron deficiency. To reduce this risk, chelated forms of manganese, zinc, and copper are often preferred when chelated iron is used.

Additional Stability Considerations with Chelates

While chelates improve micronutrient availability, they are still subject to degradation. Chelate stability can be reduced by:

• Exposure to light, UV, or ozone
• High temperatures
• Microbial activity
• Extremely low pH in concentrated stock solutions

In recirculating systems or where water disinfection is used, chelated micronutrients may need to be replenished after treatment to maintain consistent availability.

Key Takeaways

• Chelated micronutrients improve availability by protecting nutrients from precipitation and oxidation
• Sulphate micronutrients are more prone to losses, especially at higher pH
• Iron is the most commonly chelated micronutrient due to its sensitivity to pH
• Selecting the correct iron chelate depends on root-zone pH
• Mixing sulphate micronutrients with chelated iron can reduce iron availability

Looking for More Information?

Micronutrient management depends on crop type, growing medium, water quality, and pH. For guidance on chelated micronutrient selection, compatibility considerations, and application strategies, contact one of our authorized Plant-Prod distributors for local support and recommendations.