@kbellfoy Is your Ca supplement Dry or liquid? Does it contain any other compounds (I.e. Nitate)?
The 5:1 ratio (ppm) or 3:1 ratio (moles) is something that's evolved out of agriculture / natural open soils. There are many factors that "can" alter the optimal ratio in closed potted mediums / environments. For instance, in general, Mg ppms in potted mediums are typically a fair bit higher than natural soil Mg ppms. Depending on the level of required Mg for your environment; it may be tough to practicably achieve a 5:1 ratio.
Personally and IMHO, if neither element shows deficient; then the ratio is most technically not important. (this of course looking from a ppm in nutrient solution point of view and not soil CEC saturation).
While it seems that Ca levels in various environments can vary widely along with demands; levels required to show Mg- don't "seem" to be quite as varied. Again IMHO, I would feel comfortable saying that in normal strength nutrient solutions (i.e. 1.2-1.8 ec); I would expect that Mg levels below 25ppm could show deficient in some situations. That 40 ppm would rarely show deficiencies in most all situations.
If you add epsom; 1 gram per gallon equals appx. 26 ppm of Mg and 34 ppm of S. Depending on if you have other sources of Mg in your mix; 1 gram should be fine there.
If your Ca supplement is DRY and 15%; then 3.25 grams per gallon equals appx. 129 ppm.
1 Gram of epsom and 3.25 grams of 15% Ca would net you a 5:1 ratio of
Ca/Mg.
Suppose in Agriculture, Calcium Chloride is the number one form used for Foliar.
@clutch419 Ca does absorb into plant tissues; however leaf A cannot help leaf B. As well it is very difficult to correct a visible Ca- as the plant has to absorb Ca above and beyond regular utilization; when already deficient. These things(along with other factors) can alter the perception of whether a foliar spray is helping or not.
Here's a good paper involving absorption and movement of elements in plant tissues that also includes Ca.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC540953/pdf/plntphys00369-0052.pdf
Of note from the paper with Ca:
The absorption rates of calcium (Ca45), strontium (Sr89) and barium (BaLa140) are closely parallel. Whereas transport from the site of application into adjacent leaf tissue is appreciable, export from the treated leaf is negligible. The almost complete absence of basipetal transport of Ca45 verifies previous reports by the authors (5,6,20) as well as others (2,14).
......
The immobility of calcium, strontium and barium is attributed to failure of phloem transport, and polar movement.
There is a nice chart for absorption vs time too; you can see Ca absorbs as well if not better than several others.
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