Foliar feeding is essentially spraying a plant’s foliage with a diluted fertilizer mixture. A medical marijuana plant’s leaf contains small pores known as stomata. When foliar sprays are applied, the plant can absorb nutrients through its stomata or through the epidermis (the outermost layer of cells on the leaf). The advantages of foliar feeding are an almost instant absorption of nutrients and the ability to supplement the nutrients that are difficult to produce in the soil or hydroponic solution.
Foliar feeding works best when done right before the lights turn on in your indoor garden. Warmer temperatures associated with HID lights tend to close the stomata on the leaves, making absorption less effective. I like to mix my foliar fertilizers at 1/4 the strength of my root applications. Due to the fast absorption, a full strength fertilizer can result in severe burning or nutrient lock up (this is very similar to nutrient overdose within the root mass).
I prefer a light misting of all the foliage and I try to avoid “soaking” the plant leaves. A great tool to invest in is a fogger/mister. A fogger/mister can evenly distribute foliar applications with little effort. This also makes it a lot easier to maintain a consistent schedule with foliar feeding applications because the task is not such a burden.
During the vegetative cycle, I foliar feed once a week with a 1/4 strength grow fertilizer, calcium and magnesium supplement and a quality kelp formula. If you are only going to choose one product to apply as a foliar feed, I recommend a kelp formula such as Advanced Nutrient’s Nirvana. Kelp is perfect for foliar applications because it contains many trace elements and plant hormones that are very difficult to amend into a soil or hydroponic system.
Once a week during the blooming cycle, I apply a 1/4 strength bloom fertilizer, calcium and magnesium supplement and a kelp formula. I apply foliar during blooming until I see flowers develop. After flowers establish, I halt my foliar feeding program. This is not because it would be ineffective but because I worry about adding moisture to my flowers and making them susceptible to mold or rot.
Another great use for foliar feeding is in times of nutrient deficiency. Because foliar feeding gets the nutrients into the plants more quickly than conventional root feeding, correcting nutrient deficiencies can be done without delay.
If you notice a deficiency, mix up a foliar spray to apply the next morning. After application, it should only take a couple of days and the deficiency will be visibly corrected. This process can take weeks with root feeding and, as we all know, time is of the essence when trying to grow the best marijuana crop.