Plants take up nutrients mainly through the root system. They need to be fertilised by topdressing in a planned manner and well in advance, while foliar feeding can only be given to the plants. Such feeding may be necessary when the uptake of nutrients by the root system is too slow.
This can occur, for example, in the intensive growth phase of the plant. Nutrient uptake can also be hindered by water shortages, too low temperatures or an incorrect soil pH. Foliar feeding is a very effective way of replenishing nutrients, as they can be used almost immediately. It is the fastest intervention in case of micronutrient deficiencies, as well as magnesium, nitrogen and potassium. In order for foliar fertilisation to be effective, it should be done under conditions that encourage good uptake of the nutrients by the foliage (suitable weather conditions) and the ingredients used should be in a suitable form, e.g. chelated.
The uptake of nutrients takes place through all the above-ground organs of the plant, not just the leaves, which is why you may also come across the term ‘extra-root feeding’, which is, however, less commonly used.