About Foliar Feeding

Most plants can absorb nutrients through the leaves or even the stems, in addition to the roots. Absorption may be less effective and costs are certainly greater than for fertilizers applied through soil. Also special precautions must be taken not to overdose so that foliage is burned.
This method stimulates a plant quickly, providing a sort of "shot in the arm" for languishing vegetation. Since these fertilizers are applied in solution, they are of course immediately absorbed. A chlorotic lawn sprayed with iron sulfate solution greens up within minutes. Roses sprayed with a soluble fertilizer may have darker green leaves within hours.

The analysis of a foliar fertilizer may run a bit higher in the scale than that of dry granular types. Even so, by the time the fertilizer is diluted for solution, total nutrient is not great. One of the biggest drawbacks to foliar feeding is that insufficient nutrients are applied to be enduring, or to justify the trouble.
To apply dissolved fertilizers, a sprinkling can or small hand sprayer can be used for individual plants or small beds. But when it comes to bigger gardens or lawns, you will probably want to use a siphon attachment on the garden hose. Inexpensive devices of this sort do a very nice job metering concentrated solution into the water stream. You regulate the outflow by covering a hole with the thumb (for suction); water alone issues when the thumb is removed:
By and large, foliar feeding is of limited practicality. It may lend itself to combination feeding-spraying for pests.

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