It is difficult for me to take a stance that is contrary to one of the best minds on Bonsainut, but I completely disagree with this statement.
My first experience with foliar feeding was 58 years ago when I was 13. I worked part time for a landscape nursery in Northern Virginia just outside the District of Columbia. About every Saturday or every other, the owner, an older gentleman who reminded me of Colonel Sanders, had me spay all the plants with a liquid fertilizer called Rapid Grow. I don't even know if it is still available or whether it has been replaced entirely with Miracle Grow. At any rate, the plants were almost never spayed to the point of any negotiable runoff, but simply to wet the foliage. In fact, the owner insisted on never spaying the foliage if the plants themselves were dry. Plants were always watered the day before or in some cases several hours before the application of foliage fertilizer. There was always an amazing response to these foliar feedings, not just in rapid plant growth but also in the deep green color the plants responded with. During the summer when I was sometimes away or otherwise involved, I would come back and see that the plants looked a bit "lacking" compared to the way they looked when sprayed every week or two.
It stuck with me and I foliar feed to this day with a compression sprayer, not to wet the soil, but to wet the foliage. This is particularly evident when you fertilize a tree that is in the ground and well established. It would take a lot of water and time to wet the roots and probably several containers of mixed fertilizer. A foliar feeding might only be a few ounces or a bit more for a larger plant, to achieve the results I have continually experienced.
I think we tend to forget how clever plants really are. Its not all textbook plant physiology.
In this regard, an interesting experience I had about ten years ago confirmed for me once and for all how valuable a tool foliar feeding can be when using the correct spray for the job. I had a couple apple trees that constantly had aphids and other insect problems despite using both organic and chemical pest control measures. After spaying with fish emulsion and kelp the problem went away rapidly. Make of this what you will, but tomorrow I spray with this solution as I have been doing for many years.