Foliar feeding involves spaying fertilizers directly onto plants’ foliage. This type of fertilizing is very fast-acting, because the nutrients are immediately assimilated and used by the plants.
Foliar feeding is especially useful for plants that have suffered stress (from transplanting, frost, winds, heat or drought) or with serious nutrient deficiencies. It is used mainly for supplemental fertilizing.
The nutrients contained in the fertilizers penetrate the leaves through tiny openings called stomata. Since most of these openings are on the underside of the leaves, it is important to keep this in mind when applying fertilizer, and spray the underside of the foliage.
Foliar fertilizer is best absorbed if applied early in the morning or in the evening. The cooler air and higher relative humidity at those times encourage the stomata to open up.
Misting is the best method for foliar feeding because it is easier for the fine droplets to penetrate the stomata. To help the fertilize adhere to the foliage, you can add a few drops of liquid dish soap (one to two drops to 4.5 litres of fertilizer solution).
The most commonly used types of fertilizers for foliar feeding are in liquid or soluble form. Seaweed-based fertilizers, fish emulsion and plant tea are particularly effective. You can also buy ready-mixed fertilizer formulas for various types of plants, especially indoor ones. To deal with a mineral deficiency, you can even find fertilizers containing only the missing nutrient.
Foliar feeding is a short-term solution to deficiency problems. For a longer-term solution, you have to address the cause of the imbalance. If the mineral deficiency is the result of overly acidic pH, for instance, you will need to add amendments to your soil.