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Quote:

Originally Posted by ArronOB (Post 1010092)

Ray and Fred. My understanding of how plants work is that they are entirely passive about what enters their root tissues. By that I mean they have no mechanism to select one chemical other another.

Courtesy of my discussions with pro's in the industry, it appears that there are three modes-of-absorption (my terms used below).

"Passive" - the amount of nutrition taken up is directly related to the concentration in the rhizosphere. Most nutrient ions fall in this category.

"Accumulative" - the plant actively absorbs as much as is present, even if it is more than it needs, storing the excess away in cell vacuoles. Potassium is definitely in this category, and I believe boron, as well.

"Supplementive" - If the plant is deficient in the ion, it will absorb it; if not, it won't. I suspect this would apply primarily to micronutrients that aren't typically consumed during the chemical processing that goes on within a plant.

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If they are exposed to both the good elements of fertilizer and the bad ‘salts’ in a fertilising event, then don’t they take both into their roots indiscriminately. Isn’t the problem then simply too much fertilizer? Get the quantity of fertilizer right and there won’t be any ‘salts’ hanging around building up their toxicity?

There are a couple of things to address here.

First of all, with the exception of the iron-EDTA, all fertilizer ingredients are "salts", so there are no "good ingredients" and "bad salts".

Secondly, we must understand that an orchid does not take up nearly the amount of fertilizer applied, because the root system is so limited. A terrestrial plant, having such a dense, extensive network of filamentous roots, does take up pretty much everything applied, but an orchid, having a handful of "worm-like" roots, does not occupy but a relatively tiny fraction of the container volume, and it only absorbs what comes in direct contact with them, leaving a lot of soaked media to dry out with none of the minerals removed.