Micronutrient Toxicity

Micronutrient Toxicity Visual Symptoms:

The micronutrients boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn) are all essential elements for plant growth. They are required in limited quantities, and thus if supplied at higher levels then toxicity symptoms can develop.

Micronutrient toxicities will first appear in the lower leaves or older foliage of the plant. Micronutrient toxicities can be caused by multiple factors, including a fertilizer regime with excess concentrations of these elements. This can happen because of an initial mixing error where a stock tank’s concentration is too high, an improperly calibrated injector that overfeeds the plants, or a pH imbalance in the substrate.

Toxicity Prevention

There are many steps growers can take to prevent a toxicity and retain a balance fertility program, such as understanding the narrow ranges of micronutrient fertility, regularly sampling irrigation water, and monitoring substrate/fertilizer solution pH weekly. Low and high substrate pH can cause various problems for cannabis growers with regard to micronutrients. When substrate pH falls below 5, increased micronutrient availability can occur, potentially leading to excessive, toxic uptake of Fe and Mn. Monitoring substrate pH to keep it within the recommended range of 5.5 to 6.5 helps to ensure optimal root zone conditions are maintained to maximize plant growth. Adding liming materials to soil or substrate is one of the most common methods to raise substrate pH, as it reduces the toxic effects of exchangeable aluminum (Al) and Mn ions and increases the base saturation of the substrate.

Additional Information:

When Micronutrients become Macro Problems

New Research Results: Optimal pH for Cannabis

Hit the Boron 'Sweet Spot'

Characterization of Nutrient Disorders of Cannabis sativa