Last week Cory, from The Greenhouse Project, and I were discussing if foliar fertilization of plants was effective. He regularly sprays compost tea and other organic fertilizers on the vegetables in the greenhouse.
According to A.K. Srivastava, National Research Centre for Citrus in India, various plant factors influence whether foliar-applied fertilizers work. These factors include the age of leaves, the thickness of the waxy surface of leaves, the structure of the pores on leaf surfaces and their absorbing capacity, the hairs on roots and leaves, how much moisture leaves contain or is on their surface, the mineral composition of leaves, the cultivar type, and the stage of growth.
For foliar fertilization to be effective, an accurate diagnosis of nutrient deficiency is essential. It may take more than one foliar application for a nutrient deficiency to be resolved. If the nutrient concentration in the mixture is too strong or the temperature is high during or after application, leaves can be burned and plants can suffer. For foliar fertilization to work, the nutrients being applied need to be water-soluble and able to move through the nutrient transport vascular system of the plant called the phloem.
Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Washington State University, writes in her online gardening blog plants have evolved “to take up nutrients from the soil through their ROOTS.” She goes onto say foliar fertilizing is merely a short-term solution that treats symptoms rather than solving the cause of the nutrient deficiency in the soil or figuring out why the plant can’t absorb the nutrient it needs.
“Foliar feeding is yet another agricultural practice best suited to intensive crop production under specific soil limitations rather than as a landscape management tool” (Chalker-Scott). She reports foliar feeding works better on greenhouse plants than outdoor plants since the leaf surface of plants in a greenhouse is thinner and more porous and able to absorb nutrients more readily. She also mentions plants in an arid environment, which of course we have here in Nevada, have thick, non-porous leaf surfaces and aren’t good candidates for foliar feeding success. According to Chalker-Scott, the research doesn’t support the practice of using foliar applications of fertilizer for landscape plants. The best practice to provide your landscape plants with proper nutrition is to focus on building up your soil with organic matter, such as compost or humus, and fertilizing through the soil. However, foliar fertilization of crops can complement soil fertilization.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.