While we're on (or were on) the subject of foliar feeding, I found this bit of research that's more recent than the stuff originally done with radioactive nutes in the 50s.
Foliar feeding has been the subject of much debate in recent years. The practice involves applying water-based fertilizers to the leaves of plants to enhance their nutritional status. Claims of yield increases up to 20 percent have been made based on the assumption that leaves are more efficient...
ipm.missouri.edu
Among other things, it says:
"Research has revealed, however, nutrients are more likely to be taken in through the leaf cuticle [rather than the stomata]
. The latter contains a pathway of extremely minute pores (< 1 nm in diameter) with a density of about ten billion pores per cm3 of leaf surface area. These micro-pores are lined with negative charges which tend to attract (when in ionic form) positively charged elements such as calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium-form nitrogen (NH+), etc. Movement through the cuticle is dependent upon a number of factors including, nutrient concentration, molecule size, organic vs. inorganic, etc.
"Conversely, negatively charged essential elements in ionic form such as phosphorous (HPO4-2), sulfur (SO4-2) and nitrate-form nitrogen (NO3-1) find leaf entry through the cuticle more challenging. Whereas opposite charges attract, like charges repel one another."
So while the cuticle may take up Ca, Mg, K, and ammoniacal N, it will have a harder time with P, S, or nitrate N. The article says other things as well...it's pretty sciencey!
. Not liking the season's cooling either. I'm changing from venting out to in this year. Maybe that'll help my poor popsicle rooted ladies later. 
)
