Foliar Fertilization and its Role in Vegetable Production

Nutrients can be absorbed through the leaves of plants, but the small amounts of nutrients that can be absorbed are insufficient to meet the overall nutritional demands of vegetables or small fruit crops.

Foliar fertilization is best utilized when a nutritional deficiency has been confirmed by tissue analysis or by visual symptoms. Under certain soil conditions like high soil pH, excess soil moisture, and/or cool soil temperatures, some nutrients may not be readily available for uptake by vegetables or small fruit crops. When this occurs the quickest means to correct a nutrient deficiency or nutrient shortfall is through foliar fertilization.

From a practical standpoint, most fertilizers have the potential to injure plants when applied as foliar fertilizers unless they are sufficiently diluted. If a grower does not mix and apply foliar fertilizers correctly, significant plant injury (burning) may be observed. Routine usage of foliar fertilizers is not recommended and should not be practiced unless a documented need has been established through tissue analysis or visual symptoms.

Micronutrient deficiencies are frequently observed in crops growing in high-pH soils. While the best long-term solution may be to lower the pH of the soil using sulfur or iron sulfate, some growers may find that in-season pH correction is somewhat difficult in plasticulture systems. When in-season soil pH adjustments are impractical, a grower may correct micronutrient deficiencies in growing crops through foliar fertilization.

Micronutrients like boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc are required in much smaller amounts than the other essential nutrients by vegetables and small fruit crops. Most mineral soils have an ample supply of micronutrients. Still, deficiencies may be observed when the soil pH is too high, or nutritional imbalances may limit micronutrient uptake. Vegetables and small fruit crops vary in their response to applications of specific micronutrients when deficiencies are documented. Crops that have a high response to corrective applications of specific micronutrients when deficiencies occur are listed in the table below.

*Adapted from R. F. Lucas and B. D. Knezek. 1973. Climatic and Soil Conditions Promoting Micronutrient Deficiencies in Plants. Micronutrients in Agriculture. Soil Science Soc. of America.

When considering foliar fertilization to correct micronutrient deficiencies in vegetables and small fruit crops, please first confirm the deficiency with tissue analysis. Once the specific deficiency has been confirmed, select the appropriate labeled product for use on the crop that will work well in your production system. Read the product or fertilizer label thoroughly and ensure you adhere to all mixing and application directions. Over-application of micronutrients can result in phytotoxicity and/or micronutrient toxicity.