Foliar fertilization is the application via spraying of nutrients to plant leaves and stems. Foliar feeding has been used as a means of supplying supplemental doses of minor and major nutrients, plant hormones and other beneficial substances.
High concentrated sprays have potential to burn the foliage
Spray solution should be in near neutral range (6.5-7.5).
Increase pH: baking soda
Decrease pH: lime, vinegar, tamarind
Always delay foliar fertilization until air temperature drops to 26°C (80°F) or below as absorption at higher temperature is very poor because plant stomata are closed.
Otherwise, the feeding can be done in the evening or early in the morning. Absorption is further enhanced when weather conditions are humid and moist. The presence of heavy dew on the leaves facilitates foliar feeding. Addition of surfactant to solution decreases surface tension on the leaf and may increase absorption. (Note: possible chemical interactions should be considered).
Foliar nutrition is not prime method of feeding the plants and hence should not be used as substitute of soil application. Instead, it should be used to correct the nutrient deficiencies, pest resistance.