Foliar feeding consists of spraying the leaves of a plant with a nutrient solution. Foliar-applied nutrients are absorbed and used by the plant quite rapidly. Absorption begins within minutes after application and with most nutrients it is completed within 1 to 2 days.
Nutrients should be in a form that is immediately available to plants. Select liquid or soluble fertilizers with the nitrogen in the form of nitrate. Dilute the fertilizer as directed on the label for foliar feeding, or to 1/2 the strength recommended for frequent feeding. If the fertilizer does not contain a spreader-sticker to keep the drops from beading on waxy leaf surfaces, add a little, according to label instructions.
Spray to the drip point, when spray begins to drop from the leaves. Leaves absorb the nutrients best in mild weather. Don’t apply them during very hot or very cold weather. Don’t wet the leaves for a couple of days after feeding.
Foliar nutrition is a supplement to soil nutrition, not a substitute for it; but it can be useful:
When Micronutrients Such as Iron or Zinc are Locked in the Soil
Alkaline conditions cause some micronutrients, particularly iron and zinc, to form insoluble compounds and become unavailable to plants. You can correct this condition by adjusting the soil pH to make it more acid, but this adjustment may take weeks to release the nutrients. A foliar feeding of micronutrients will feed the plants until the soil nutrients become available again. Some plants—notable azaleas, rhododendrons, camellias, and blueberries—cannot extract iron unless the soil is quite acid, and may need this treatment even in slightly acid soil.
This is the most common use of foliar feeding.
To Aid Transplants
Newly transplanted plants may benefit from foliar sprays. Until new roots are formed, the plant is completely dependent upon stored nutrients to maintain itself. When these stored nutrients are used up or are deficient, the ability of the plant to become established is greatly reduced. Foliar nutrient sprays may alleviate this problem.
When a Quick Growth Response is Wanted
If plant growth slows down or nutrient deficiency symptoms appear, a foliar feeding at the same time as adding fertilizer to the soil will speed up the response to the fertilizer.
When The Soil is too Cold For Conversion of Nutrient Elements into Usable Forms
For perennial plants, early spring growth is limited by cold soil, even when the air is warm. Under such conditions, soil microorganisms are not active to convert nutrients into forms available for roots to absorb. Yet, if the nutrients were available, the plant could grow. A nutrient spray to the foliage will provide the needed nutrients immediately to the plants, allowing the plant to begin growth before the roots are able to absorb nutrients from the soil.
To “Push” a Plant
To get the very best growth from a plant, such as to grow a prize-winning pumpkin, spray it weekly with a nutrient solution. This method avoids any deficiencies in the mechanism that takes up nutrients from the soil and guarantees that the leaves have all the nutrients they need to work at top speed.