Understanding the foliar nutrition

[Ravi]

Why foliar nutrition? Excerpts from Midwest Labs, Omaha.
Supplying the major nutrients NPK is most effective and economical means via soil application, foliar application is excellent method for supplying the plants secondary nutrients eg. Calcium, Magnesium and Sulphur and micro nutrients Zinc, Manganese, Iron, Copper , Boron and Molybdenum . Primary foliar feeding intends to delay natural senescence processes shortly at the end of the reproductive growth stages . Foliar feeding targets the growth stages where declining rates of photosynthesis and levelling of root growth occurs.
Mechanism of action: absorption through stomata and Epidermis..
Efficacy of foliar feed: 95%
References:
Midwest Labs entitled “ foliar nutrition” for an exhaustive research article.
https://www.royalqueenseeds.com>blog. On mechanism of absorption.
Can foliar feed benefit the orchid?

[Roberta]

I doubt very much that foliar feeding does much for orchids - orchid leaves often have a water-repellent cuticle on the top surface - this protects the plant from desiccation. So any water/fertilizer that you spray on the leaves will mostly roll off. But then, it ends up in the medium where it gets picked up by the roots. So if foliar feeding helps the orchid, it's only because it ends up on the roots anyway. Why not skip the water/fertilizer spotting that the leaves will acquire this way and just put the fertilizer in the root area in the first place?

[Ray]

Roberta is correct, but I'll add that it is all (like most things) a matter of degree.

Very young, ex-flask phalaenopsis, for example, will absorb nutrients through the leaves better than will a mature one that has developed a thick cuticle layer.

A cymbidium will do so better than a phalaenopsis, but again echoing Roberta, why bother?

[Ravi]

What about the secondary and micronutrients listed in the research article? Don’t they have any role at all in the orchids?? Fact remains that an orchid is a plant and a plant , what applies to the plant kingdom by and large should also apply on the face of it .Does it mean that an orchid when it acquires water repellant cuticle is totally impervious to the supply of any nutrient via foliar route? What about the stomata which is the route of absorption? Surely, they are patent.
Life sciences are rapidly evolving areas of research may be one day some new view may emerge to the unanswered questions.
Kindly consider my contradictions as purely academic.
Ray has an interesting observation a good one at that!
Thanx both of you for enriching my knowledge .

[Roberta]

The micronutrients, major nutrients, and water, all go through the roots quite efficiently. And orchids have evolved to be very efficient, needing very little in the way of nutrients. (If you are growing on the side of a tree, you have to get by on nutrients from decaying detritus that get dissolved in rain. And you have to avoid desiccation when the sun comes out) Roots do an excellent job of capturing the water and nutrients. Leaves do an excellent job of controlling water loss along with their photosynthesis. It makes sense to put the nutrients where they will be efficiently absorbed, and not put stuff on the leaves that will leave deposits that look ugly and may even interfere with photosynthesis if they block enough light.