Foliar Feeding
Foliar feeding is a common practice of supplying
nutrients to plants through their foliage. It involves
spraying water-dissolved fertilizers directly on the
leaves.
Many believe that foliar feeding is favorable over
soil application and it is associated with higher
yields, and better fruit quality.
However, many open questions and uncertainty still
surround this practice.
Under Which Conditions Should You Use Foliar
Feeding?
Under certain conditions, foliar feeding has an
advantage over soil applications.
Limiting conditions - A foliar feeding is
recommended when environmental conditions limit
the uptake of nutrients by roots. Such conditions
may include high or low soil pH, temperature stress,
too low or too high soil moisture, root disease,
presence of pests that affect nutrient uptake,
nutrient imbalances in soil etc.
For example, micronutrient availability is greatly
reduced in high soil pH. Under such conditions,
foliar application of micronutrients might be the
more efficient way to supply micronutrients to the
plant.
Nutrient deficiency symptoms -
One of the
advantages of foliar feeding is the quick response
of the plant to the nutrient application.
The efficiency of nutrient uptake is considered to be
8-9 folds higher when nutrients are applied to the
leaves, when compared with nutrients applied to
soil.
Therefore, when a deficiency symptom shows up, a
quick, but temporary fix, would be applying the
deficient nutrient through foliar application.
In specific growth stages – Plants require different
amounts of nutrients in different growth stages. It is
sometimes difficult to control the nutrient balance in
soil. Foliar applications of essential nutrients during
key stages can improve yield and quality.

Limitations of Foliar Feeding
Limited dosage - Nutrients applied in foliar
application cannot meet the entire nutrient
requirements of the crop.
Phytotoxicity - Applying high concentrations of
nutrients by foliar application might result in leaf
burn, as water evaporates and salts remain on the
leaves.
High cost – Due to phytotoxicity considerations,
small amounts of nutrients should be applied at a
higher frequency. However, frequent applications at
lower concentrations are very costly and not
practical.
How to Improve the Effectiveness of Foliar Feeding
Various factors affect the effectiveness of foliar
feeding:
pH of the foliar spray solution – Nutrients must be
in their soluble form in order for the plant to be able
to absorb them. pH affects the solubility of nutrients
and their interaction with other components in the
water. Generally, acidic pH improves the
penetration of nutrients through leaf surfaces.
In addition, pH affects foliar absorption of nutrients
in three other ways:
1. pH affects the charge of the cuticle (a waxy layer
covering the leaves) and
therefore its selectivity to ions.
2. The ionic form of nutrients is pH dependent, and
therefore pH can affect
the penetration rate.
3. pH might affect the phytotoxicity of the sprayed
compounds.
We can conclude that pH of the spray solution must
be adjusted according to the applied nutrient.
Use of surfactants – Surfactants contribute to a
more uniform coverage of the foliage. They
increase the retention of the spray solution by
reducing the surface tension of the droplets.
Without surfactant With
surfactant

Time of the day - the best time to foliar feed is early
morning or late evening, when the stomata are
open. Foliar feeding is not recommended when
temperature exceeds 80°F ( 27° C).
Droplet size – Smaller droplets cover a larger area
and increase efficiency of foliar applications.
However, when droplets are too small (less than
100 microns), a drift might occur.
Spray volume - Spray volume has a significant
effect on the nutrient absorption efficiency. Spray
volume must be such that it is sufficient to fully
cover the plant canopy, but not too high so it does
not run off the leaves.

source: www.smart-fertilizer.com/articles/foliar-feeding