Is Foliar Feeding Effective?
As organic gardeners, we are constantly reminded to feed our soil, not our plants. But there are circumstances where we want to directly feed our plants through foliar feeding.
Foliar feeding can give plants a direct boost of nutrients through their leaves. This is done by means of thousands of microscopic pores on leaf surfaces. These openings, called stomata (Greek: stoma, meaning “mouth”) are located primarily on the underside of the leaves. This prevents them from plugging up with dust and other environmental contaminants and also prevents fungal spores from entering. The primary functions of stomata openings are to permit gases containing carbon, hydrogen and oxygen to enter the plant. These are then used to manufacture sugars during photosynthesis. Conversely, stomata allow water vapor to escape from plants. In most cases, stomata close at night because the absorption of carbon dioxide is unnecessary when photosynthesis is not taking place. Stomata may also close on hot, dry days, in heavy winds or when the soil becomes dry.
We can use these stomata openings to help increase a plants growth, health, and overall production through the application an organic fertilizer in the form of a foliar spray. The stomata are able to absorb dissolved nutrients and minerals and translocate them to the parts of the plant where they are needed.
It is effective as a short term measure for ensuring healthy plants within a long term soil building program. Nothing can replace feeding the soil, but foliar applications can be a good addition at certain times of the year or as a strategy and remedy for nutrient deficiencies, until the soil is able to supply them. Supplementary foliar feeding may also be necessary as an annual practice in some soil and climate situations. For example, in cold northern soils, foliar fertilizer may be necessary each spring to supply nitrogen, phosphorous, and other essential nutrients until the soil warms up and nutrients become available from the soil.
When To Foliar Spray
The best time to spray is late in the afternoon or in the early dawn, when temperatures are mild and wind is minimal. When wind is minimal, finely atomized sprays drift readily. This is most desirable. Absorption is further enhanced when weather conditions are humid and moist. The presence of dew on leaves facilitates foliar feeding. Absorption is maximized when sprays coat the underside of leaves where the majority of the stomata are located.
When Not To Foliar Spray
It is best not to use this method when it is windy and dry. When the air temperature reaches or exceeds 80° F, absorption is very poor, because plant stomata are closed. Avoid spraying during the height of solar indexing (10:00 AM to 4:00 PM) to avoid burning the leaves.
For Best Results
Be certain to read all product labels. Apply a small amount of fertilizer to start until you know how your plants will respond. Sometimes using a small amount of surfactant added to the mix will decrease surface tension on the leaf and better facilitate absorption.
You can use any kind of sprayer to apply foliar fertilizers, keeping in mind that you want the finest mist possible. The finer the mist, the more easily it will be absorbed by the stomata openings. Hand pump sprayers or even hose-end sprayers will work just fine.
Happy and healthy gardening,
Milo Lou Shammas
Founder and Formulator