To Feed or Not to Foliar Feed?

What’s the best nutrient feeding method for your urban, hydroponic, aquaponic, indoor, organic, greenhouse, or vertical tomato garden? There are many ways — and many climates — in which to grow tomatoes. No single fertilizer solution will work for everyone. Visual and soil analysis will help you develop the right solutions and a growth plan, but it will mean trading benefits and drawbacks. All plant leaves uptake foliar nutrients through tiny openings called stomata. Stomata are usually located on the underside of leaves and act primarily to allow the transfer of oxygen and water out of the plant (transpiration) and carbon dioxide into it.

Drawbacks

• Building healthy organic living soil full of beneficial fungi and bacteria is essential and necessary for optimum plant health and production. It is impractical to try to meet a plant’s total nutrient requirements through foliar feeding.
• Your plants get their needed Nitrogen, Phosphorus, and (K) Potassium mainly from root feeding. Foliar feeding is not meant to be a substitute for a good soil fertility program, but it could be a supplement to one. Certain tomato cultivars are bred to be resistant (VFN), but all tomato varieties are not immune to issues related to moist conditions, such as vascular wilts, fungal diseases, early blight, and septoria.
• If you try this method, test spray a plant with an atomized mist of your selected solution to check for its response before doing a widespread application. If concentrations of nutrients in the foliar spray are too high, leaf damage can occur. Keep in mind that certain regions have higher rain levels and humid climates.
  

Benefits

• Certain soil conditions — such as low or high pH, excessive moisture, drought, or temperature fluctuations — may cause some nutrients to be unavailable for root uptake. If any of these conditions exists, the problem may be more effectively corrected with foliar applications than with soil applications.
  

  

• Foliar feeding has been shown to be helpful in the earlier growth stages of the plant, and preventive measures can be applied, as in the spraying of calcium to ward off blossom end rot and increase blossom set prior to fruit production.
• Micronutrients such as zinc, iron, boron, and copper have quicker uptake using this method. Under high pH conditions, iron chlorosis or yellowing occurs on young leaves and can be alleviated by the application of iron sulfate. Strategic applications to counteract specific deficiencies would need to be analyzed to target effective solutions.

Final Notes

It is important to include a surfactant or wetting agent in your solution to allow for better coverage of the leaf. If it rains after an application, most of the spray will be washed off the leaves and reapplication will be necessary. Also, do not foliar feed in direct sunlight — the heat will cause the liquid to act as a lens and burn the leaf. The best time for application is in the early morning, which allows the leaves to dry during the day.