Foliar fertilizers are a specialized group of plant nutritional products that have been specifically adapted for application directly onto the plant’s leaves with much faster nutrient availability than conventional root fertilization. Foliar fertilizer technology is a unique, dynamic and effective method of crop nutrition.

This method of application is an excellent way of supplying nutrients to the plants throughout the life cycle and has become a very important tool in the agronomist’s armory. Nutrients that have been dissolved in a liquid carrier can be directly absorbed through the surface of the leaf, which can enlarge or shrink in response to changes in the plant’s environment.

Foliar feeding is particularly valuable when the plant’s roots are not absorbing optimally or there is a problem with the nutrition from the soil itself. This can occur during extremes of cold or heat, excesses of competitive weeds, nematodes or very alkaline soil. Foliar feeding is a supplemental method of plant feeding. Foliar fertilizers are easy to blend and simple to handle and apply and can easily be mixed with crop protection products while granular fertilizers are cheaper in bulk and offer slow-release coated options. Now that we’ve seen what foliar fertilizers are, let’s take look at how they work.

How do foliar fertilizers work?

Because certain fertilizer nutrients are water-soluble and can be directly applied to the leaves of plants, foliar fertilizers can play a major role in plant nutrition. To fully understand how foliar fertilizers work, we need to first understand the anatomy of the plant’s leaf tissue.

The entire leaf is surrounded on both the top and bottom by a layer of tissue called the epidermis, much like in the human skin. This layer protects the plant from excessive water loss and supplies a barrier to the outside environment. The top surface of the epidermis is coated in a waxy layer called the cuticle. Due to its hydrophobic nature, the cuticle naturally repels water from the surface of the leaf and protects the plant against outside stressors and excessive water loss. The next layer, the mesophyll, is sandwiched between the two outer layers of the epidermis and is the area in the leaf where photosynthesis takes place and houses the plant’s equivalent of our circulatory system. Small openings in the epidermis of the plant called stomata regulate the movement of oxygen in and carbon dioxide out of the leaf during photosynthesis.

Foliar fertilizer, with its water-soluble components, can enter the leaf either by penetrating the cuticle or by entering through the stomata, which can then be taken up and used in the plant’s physiological processes and metabolism. The cuticle is also a dynamic layer and changes thickness in response to environmental factors, like water deficits. Although the waxy cuticle presents a physical barrier to the foliar nutrients, the bulk of foliar fertilizer is absorbed through the cuticle and less via the stomata. This is achieved by including surfactants or wetting agents in the fertilizer formulation to overcome the cuticle’s water-repellent nature.

Once inside the plant leaf, the nutrients stimulate leaf growth and make their way down to the plant roots and further increase growth activity. The roots, in turn, are stimulated as the plant starts to demand more water. This method of absorption can supply immediate benefits to plants that may be suffering from a particular deficiency or stress.

Foliar application of phosphate fertilizers

By applying foliar phosphate fertilizers to the leaves, the crop is given an “energy boost,” which, in turn, stimulates the growth of roots and shoots. This results in an almost immediate repair or recovery and enables the plant to build resistance and overcome other stresses later in its life cycle. This is particularly useful when there are droughts during the spring and summer months.

How, where and when to apply foliar fertilizers

Foliar fertilizers are applied to the plant’s leaves by spraying. The spray drenches the entire leaf of the plant with the nutritional product.

Cool air and high humidity are best

The best time for the application of foliar fertilizer is usually in the early morning or late afternoon, when the air is cooler and humidity is highest. During these conditions, the plant’s leaves are full of water and can absorb nutrients best.

If foliar sprays are applied when the leaves are too hot, the amount of penetration and nutrient absorption is reduced. Dew formation on the leaves aids foliar fertilization because the fertilizer already on the cuticle gets redissolved in the dew and then penetrates the plant.

Foliar feeding can be applied in either droplet forms or fine mists. Farmers need to ensure that application takes place when wind conditions are minimal to prevent the sprays from drifting away from the target plants. Foliar fertilization is most efficient when the crop is well-irrigated and the leaves are not being subjected to water stress. Foliar spraying just before rainfall reduces efficiency, as does overhead irrigation after application.

Foliar spray solutions are best when formulated with a slightly acidic pH of around 5.0. The surfactants in the spray improve the droplet distribution and reduce leaf burn or scorching and can be applied using standard irrigation spraying equipment. It’s essential to achieve full coverage of the plant canopy to maximize absorption.

It’s important to remember that foliar nutrition is a supplement to regular fertilization, because the amount of nutrients absorbed by foliar application is limited and is not sufficient to sustain the plant’s total nutritional requirements.

Foliar fertilizers are specific to the plant’s nutritional needs and are usually formulated for a particular condition and crop type. The efficiency of this type of feeding is largely dependent on factors like crop type, leaf structure, temperature, humidity, concentration, pH and physical size of the spray droplets, and the presence of a surfactant. Micronutrients are successfully applied as foliar feeds because plants need relatively small amounts of these elements and because they are readily fixed in the soil.

Advantages of foliar fertilizers

The advantages of foliar fertilizers are increased yields and better disease resistance. Plants tolerate drought better and crop quality can be improved. It also has the specific advantage of being taken up directly to the target plant organs and overcoming absorption barriers that exist in the soil due to complex interactions of pH, leaching, soil fixations, blockages and other losses.

Another major advantage of foliar feeding is that the results are almost immediate, and the effects are often dramatic. This is because most of the application finds its way into the plant, as opposed to conventional fertilization where most of the fertilizer ends up in the soil. Foliar feeding has the most dramatic effects during periods of high growth and nutrient demand. This occurs at once after germination, flowering and fruit set-in and bulking up stages of bulbs or tuber-type crops. These growth stages often determine the final crop quality and quantity.

Foliar feeds can address urgent needs very quickly and can prevent crop losses when applied timeously. In this manner, they can be used preventatively rather than after a problem has developed.

The grower has complete control

The grower can time application for immediate delivery — thus correcting damages before they become serious losses due to sudden frost, cold, heat or drought. The frequency and concentration of nutrients can be carefully controlled and applied during optimal weather conditions. Application rates are much lower than soil fertilization and represent a saving on fertilizer costs and a reduced environmental footprint.

When mixing foliar fertilizer with pesticides, the grower can achieve a synergistic effect and save on application costs. It can be used as a standalone application for phosphorus, calcium, magnesium, sulfur and trace elements where only small quantities are required. Foliar feeding can deliver macronutrients and micronutrients successfully, but is not a replacement for regular fertilizer application, but rather a supplement.

Leading in foliar fertilizers

As a global leader in fertilizer manufacture, ICL Group has developed a range of specialized foliar fertilizers and next-generation fertilizers, which include innovative products for both preventative and curative applications. These products give the plants an energy boost, so they reach full development, reduce stress, strengthen the plant’s defense systems and improve root absorption throughout their life cycle. They have been formulated to suit a wide range of crops and plants to provide the optimal composition of nutrients for growth throughout its life cycle.