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Foliar Fertilizing Cannabis Plants

The Science of Effective Foliar Sprays for Cannabis Plants

Foliar feeding offers cannabis growers the ability to supplement their regular feeding regime or to quickly overcome unforeseen nutrient deficiency. It is not however a replacement for a proper root feeding regime. Here are a few scientific principles which an understanding of will greatly increase the effectiveness of your foliar applied sprays.

Several factors to consider before applying foliar fertilizer solutions are:

  • Proper Spray Equipment
  • Fertilizer Solubility
  • Fertilizer Spray Concentration
  • Point of Deliquescence
  • Leaf Wetting
  • Solution pH
  • Electric Charge
  • Environmental Factors

Professional Spray Equipment

Choose spray equipment that is designed and built for applying fertilizers and plant protective solutions.  If you are applying OXIDIZERS like peroxide and paracetic acid products ( Zerotol, OxiPhos, Sanidate) you must choose sprayers with Stainless Steel guns and fittings. Brass is more commonly used in constructing sprayers for agricultural use, but OXIDIZER materials are corrosive enough to cause LEAD to leach from the brass fittings into your spray solutions. This is also possible when using low pH pure Reverse Osmosis filtered water in your spray tank.

Droplet Size Matters

Spray efficacy often depends on droplet size, with better coverage being achieved by smaller droplets which are more likely to be retained by the leaf surface.  By optimizing droplet size range, you will ensure your foliar sprays have the best chance of success

Formulations and Adjuvants

Foliar nutrient sprays are generally composed of two major components, namely: the active ingredient and the inert materials or adjuvants. Use of non-ionic surfactant improves leaf wetting and nutrient absorption of foliar fertilizer sprays.Adjuvants help to improve the spreading (leaf wetting) and persistence (sticking) of the active ingredients or mineral elements on the leaf surface as well as increase the rate of uptake and bio-activity of the mineral elements applied. Limitations to the foliar uptake of applied mineral elements has led to the widespread use and continuous search for adjuvants that improve the performance of spray treatments. Custom hydro recommends always using one of the high performance non-ionic surfactants we carry in your foliar fertilizer sprays for improved leaf wetting and coverage. In figure 1. you can see the effect that non uniform fertilizer spray coverage has on nutrient uptake by the plant leaves.

Most Importantly, Foliar Fertilizers Must be Completely Soluble in Water 

A list of the pure mineral and high performance chelated fertilizer compounds Custom Hydro stocks is shown in the following table. All of these fertilizers are fully water soluble and are ideal for foliar application, many with low POD (point of deliquescence).

Macro-nutrient mineral fertilizers recommended for use in foliar spray formulations.
macronutrient foliar fertilizer compound
nitrogen urea(low biuret), ammonium sulfate, calcium nitrate, magnesium nitrate, Protein Hydrolysate (Ferti-Nitro Plus, 3D Soluble Fish)
phosphorus phosphoric acid, mono potassium phosphate, mono ammonium phosphate, phosphite
potassium potassium acetate, potassium amino acid complex, potassium carbonate, MKP, potassium nitrate, potassium sulfate, potassium silicate
calcium calcium amino acid chelate, calcium chloride, calcium nitrate
magnesium Magnesium amino acid chelate, magnesium nitrate, magnesium sulfate
sulfur magnesium sulfate








Concentration of the Active Ingredients in the Final Spray Solution Is Important

A preliminary distinction should be made concerning the application of either macro or micro-nutrients, the latter being supplied at lower rates and concentrations and often being unstable when applied as inorganic salts. Still yet, the concentration of the fertilizer element in foliar spray solutions must be much higher than the relative concentration of fertilizer elements in root applied feedings. Because leaves are covered in a waxy cuticle that impedes solution penetration, higher concentrations of fertilizer elements results in higher penetration rates, up to a point. The ideal concentration range of mineral nutrient solutions for foliar application should be selected according to factors such as the kind of nutrient (e.g. macro- or micronutrient), plant species, plant age, nutritional status and weather conditions (Kannan, 2010; Wittwer and Teubner, 1959; Wojcik, 2004), and all of these will ultimately be limited by the need to avoid phyto-toxicity.

Point of Deliquescence

 The point of deliquescence is defined as the relative humidity value at which the salt becomes a solute. Thereby, the lower the point of deliquescence of a salt is, the sooner it will dissolve upon exposure to ambient relative humidity (Fernandez and Eichert, 2009). When ambient relative humidity is higher than the point of deliquescence of the foliar applied compound, the substance will dissolve and will be available for absorption by the leaf.​​​​​​​


Solution pH

Frequently foliar spray salts dissolved in pure water at high concentration will alter spray solution pH and some formulations may have extreme pH values and hence will affect the uptake process of by the foliage.​​​​​​​ Always check and adjust foliar spray solution pH prior to application to avoid inconsistencies from extremes in pH.


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