Foliar Feeding Guide: When, How, and Which Nutrients Work

You see yellowing leaves, poor fruit set, a plant under stress — yet the fertilizer you applied to the soil just isn't working. Many growers across Mediterranean and export-oriented production, both under cover and in open field, know this picture. Usually the problem is not the fertilizer itself, but the fact that the plant cannot take nutrients up through the roots at that moment. This is exactly where foliar feeding comes in.

This guide looks at when foliar feeding makes sense, how to apply it correctly, and which nutrients actually work through the leaf, from an agronomist's perspective. Let's be clear from the start: foliar feeding is not a replacement for soil nutrition — it is a complement to it. Growers who understand this distinction save both money and yield.

What is foliar feeding?

Foliar feeding is the practice of dissolving plant nutrients in water and spraying them onto the leaf surface so the plant absorbs them directly through the leaf tissue. Instead of uptake from the soil solution via the roots, the nutrient passes into the cell through the leaf cuticle and the stomatal openings.

The biggest advantage of leaf uptake is speed. A micronutrient applied to the soil can take days to reach the root and be absorbed. The same nutrient applied to the leaf enters the tissue within hours. This makes foliar application the most practical tool for urgent deficiency correction and stress periods.

However, the leaf's uptake capacity is limited. It is not possible to meet a plant's full macronutrient demand (nitrogen, phosphorus, potassium) through the leaf — those quantities are too high and would scorch the foliage. The leaf is powerful in small doses and targeted supplementation.

When does foliar feeding make sense?

Foliar application is not a cure-all. Used at the right time it is powerful; used at the wrong time it wastes money and labor. Foliar feeding genuinely makes sense in the following situations:

1. When root uptake is impaired. If soil temperature is low (early spring), the soil is waterlogged or compacted, or the root zone is weakened by disease or nematodes, the root cannot absorb nutrients. Even when nutrients are present in the soil, the plant cannot reach them. In this case the leaf builds a temporary nutrient bridge.