Zinc (Zn)

Function:

Zinc (Zn) is involved with metabolism and enzymes.

Deficiency:

Deficiency symptoms are expressed on young growth as a mottled, interveinal chlorosis (yellowing) and stunting. Excessive levels of P can have an antagonistic effect on Zn availability.

Poor bract formation due to zinc deficiency.
Click on image for larger version. (image ©Roy Larson, NCSU)

Excess:

Symptoms appear as a reduction of root growth and leaf expansion, ultimately resulting in death of the exposed parts. Excessive levels of Zn can have an antagonistic relationship with Fe, Mn, or P.

Confirm your actual Zn levels by conducting a plant tissue analysis. Root substrate (medium) tests are less reliable for determining Zn levels.

Monitoring and Management Strategy for Zinc (Zn)

Fertilization Rate:

There is a fine line between deficient and toxic levels. Use a fertilizer that provides a measured dose of Zn.

Interactions:

Excessive levels of P can have an antagonistic effect on Zn availability. Excessive levels of Zn can have an antagonistic relationship with Fe, Mn, or P.

Tissue Concentration:

Normal range is 25 to 60 ppm. Levels below 20 ppm are considered deficient and above 60 ppm are considered excessive.

Options:

Preplant:

Incorporation of a micro-nutrient mix into your soilless substrate.

Continual Fertilization:

1. Most commercial fertilizers that provide micronutrients including Zn. Remember to add supplemental Zn applications if using calcium nitrate (Ca(NO₃)₂) + potassium nitrate (KNO₃).

Corrective Fertilization:

1. Corrective applications of zinc sulfate at 13.9 ppm of Zn (see mixing rates below) for soilless substrates. A corrective fertilization of Zn will return the tissue to the normal green color within 1 to 2 weeks.

   For Corrective Application: Add 0.5 oz. (14.2 g) of zinc sulfate (36% Zn) per 100 gallons of water. Do not over apply.

Corrective Foliar Spray:

Foliar sprays have a greater risk of plant injury. Early morning applications are preferred. Avoid applications during the midday heat. Plant uptake is enhanced by the increased drying time which occurs during the moist conditions in the morning. Nutrient uptake through the leaves is also greater in the light periods than at night, thus making morning applications more desirable than evening sprays.

To apply a foliar spray of Zn: mix 2 oz. (56.7 g) of zinc sulfate per 100 gallons of water. It will give a final concentration of 56 ppm Zn. Test on a few plants first. Do not over apply.

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