'What Orchids Eat', importance of calcium

[Fabian24]

Just to make a small compilation to clarify what has been discussed so far.

Most of the premises introduced to support either the claim of potassium toxicity or the advantage of using low K-high Ca fertilizers proved to be false, unfounded or not applicable.
Namely:

Potassium binding more strongly to potting media than calcium.
No data have been shown to support this assumption.
The only info I could find (Foster, W.J., Wright, R.D, et al., J Am Soc Hortic Sci July 1983. v. 108 (4)) for pine bark contradicts this assumption, stating that for pH 5.5 Ca and K ions are adsorbed at the same rate of about 2.4 mg/10g of pine bark.

Calcium availability in nature is substatially higher than Potassium.
(“Free bioavailable K is relatively rare in the environment.... Calcium and Mg are relatively common in the soil and aquatic environment.” R. Lockwood, Orchids, March 2013)
No data presented to support this premise. Just speculation.
However, the data measured in situ by 10 different authors for different locations of Central and South America (review by Walker & Ataroff, Lyonia, Journ. Ecol and Applic. 7(2), 2004) contradict this assumption. A mean value of the measured Ca/K ratio by all these authors for vertical rain and tropical mist in different locations is 1.8 and 2.2 respectively.

Ability of orchids to uptake sufficient K from very dilute sources.
The only source presented ( R. Lockwood, Orchids, March 2013) to support this assumption is related to foliar uptake of K by epiphytic Bromeliads.( Winkler, U., G. Zotz, Ann. Bot. 106(3), 2010.). So, not applicable.
However, many publications report potassium deficiency symptoms in many orchid genera, when dilute sources of K are used as fertilizers.

Potassium poisoning
No factual evidence is given to support this claim.
On the other hand, plenty of data can be found in the literature reporting impairment of orchid growth related to excess of boron or magnesium in some commercial fertilizers. However none can be found reporting potassium poisoning for the standard potassium concentration found in most fertilizers.

Potassium toxicity of freshwater mussels.
For me this was really the most hilarious of all the attempts to justify the claims.
What has the physiology of mussels to do with orchids?
When I increase Copper levels in my aquarium shrimps die, snails die, algae die, however plants and fish are OK. Can I really infer from this fact any conclusion about Cu and orchids?

Potassium chloride injections being lethal to humans.
Another laughable statement when used in relation to K uptake in orchids. Even more laughable when one considers that thousands of people with high blood pressure consume lite-salt which generally contains 50% potassium chloride.




BUT WAIT!

There could still be the possibility that even if the assumptions were all false, empirical data could prove the claim to be true.


Unfortunately no quantifiable empirical evidence is shown that may support the claim or prove it to be valid.
The conditions of the experiments are never specified and the results are just vague or inexplicit assertions, no quantification of the improvement of any parameter is reported:

"I am pleased with the results. Leaves are larger, stiffer and shinier....
"Plants that were in decline are rebounding....
"Seedlings are transitioning out of compots into individual pots without stalling and dying.
"Four of my plants even received AOS quality awards in the last year." ( R. Lockwood, Orchids, March 2013)

(Normal fertilization regimes also make people pleased with the results, also make people win awards, also make leaves larger and shinier. Many people grow seedlings without stalling and dying, with the standard fertilization rates.)

More results:
Positive feedback from hundreds of orchid growers.
... one stated that he was happy to be able to find it commercially.
...the total number of testers is expanded.

Do you really think any of these results provide evidence of quantifiable improvements of any growth parameter?

Does any of these results show any measurable improvements in leaf span, number of flowers, flower size, flower stalk length or diameter, number of leaves, size or height of pseudobulbs, total dry matter, just to name a few parameters?

No. None of them does.


And the most ludicrous part:

When one quotes publications that clearly show quantifiable impairment of growth parameters due to K deficiency in many orchid genera, this leads to an even more absurd new claim being made:
That this is only valid for not heavy feeders, so the genus Phalaenopsis cannot be included.

Absurd, because Phalaenopsis was, according to the publication, one of the best examples of the great benefits of K-lite fertilizing:
“Four years ago this Phalaenopsis pulcherrima ‘Fuchsia Fantasy’ was a stunted purple-leaved plant the author could not get to bloom. Increasing Ca and Mg brought the plant back to green and flowering. Reducing the potassium induced the best blooming and an 86-point Award of Merit.” ( R. Lockwood, Orchids, March 2013)

(I also found a study on the not heavy feeder Dendrobium nobile and its symptoms of potassium deficiency, just to make even more clear that this “new claim” is not founded. R.G.Bichsel et al., HORTSCIENCE 43(2):328–332. 2008)


I respect every opinion, but I think there is no point in trying to sustain a rational discussion when one of the parts shows a purely dogmatic approach.