While not a substitute for healthy soil, foliar sprays are an effective way to supplement the nutritional needs of your plants. To properly use and fully benefit from your foliar sprays, keep these notes in mind:

  • Foliar feeding should be done in the early morning or late evening, and in temperatures below 75°F (24°C), since heat causes leaves’ pores (stomata) to close.
  • The underside of leaves have more stomata because less evaporation will take place in the cooler, shady underside. This means that it is important to also spray the undersides of the leaves, not just the top.
  • Clones and plants in the vegetative stage will greatly benefit from foliar feeding. Since clones have no roots, they will extremely benefit from foliar sprays as it will aid the rooting process.
  • It is recommended to avoid using foliar sprays during the flowering stage. Spraying flowers will increase their chance of developing a mold or mildew. If you need to spray during the flowering stage, it is important to keep the lights off/temperature down and to keep an eye on your flowers.
  • Plants absorb nutrients through the leaf much quicker than they do through the roots and stem.
  • Foliar sprays are typically less concentrated than soil fertilizers.
  • Fertilizers applied via foliar sprays are more effective and faster than when it is applied to the soil. However, foliar sprays are only short-term solutions for stressed plants. It’s important to remember to also pH and test the ppm of your soil runoff to determine the health of your soil and to make the appropriate changes to your reservoir/feedings.
  • Natural compounds used in sprays such as milk, kelp, compost Teas, and fish emulsion are also very beneficial.
  • Insecticidal soap and other surfactants can be used as a wetting agent to help the foliar application spread and stick to plants.
  • The pH of your foliar sprays should be slightly acidic (~5.8) to allow the solution to easily penetrate the cuticle (due to the complex electrostatic repulsion and attraction phenomena, which is regulated by pH within the cuticle) and be absorbed by the leaves. The optimum pH will vary with each nutrient and strain of plant.
  • Atomized spray nozzles are recommended as misty sprays are more efficient and will allow for better absorption and coverage. Sprays that aren’t misty won’t be as easily absorbed by the plant.

To learn more about foliar sprays and how to combat specific issues, enroll in an Oaksterdam University Horticulture course! Check out our schedule here!