Calcium and Magnesium

[Rick]

K is continually being released from the osmocote in the pots oke:

So how are you calculating your continuous/weekly/monthly K exposure concentration?

Using a slow release may be a lot less than periodic exposure to a traditional liquid fert.

 

[Stone]

So how are you calculating your continuous/weekly/monthly K exposure concentration?

Using a slow release may be a lot less than periodic exposure to a traditional liquid fert.

Me calculate? Its all guesswork:evil:

 

[keithrs]

Me calculate? Its all guesswork:evil:

A man after my own heart....

 

[Rick]

Me calculate? Its all guesswork:evil:

For instance if you are using the 19-6-12 Osmocote that recomends adding 3 tablespoons per 2X2' square (about every 4 months). That comes out to about a 1/4 tsp per 4" pot.

by the time you adjust for total available K per gram of Osmocote, spread out over 4 months, that comes out to a much smaller dose compared to the old fashioned "weakly weekly" feeding of a traditional liquid high K fert at 100ppm N.

Now the Osmocote feed is in prills that may or may not be in contact with roots, so dispersed only by watering( which in your case is with almost no K water). So watering may wash the fert out of the pot more effectively than when using a liquid feed that saturates the spongy potting media.

So you may be providing a lot less K (or anything actually) than you think you are.

 

[Brabantia]

Thank you Rick for your answer, but it is not so much the concentration in K (in KLite or other low K fertilyser)that worries me but the extreme hardening risk of leaves and their envelope when the quantities of Calcium and Magnesium distributed are too well hight ( 20 ppm Mg and 50 ppm Ca at 65 ppm N). I understand definitely that ratio N/K is too much low in MSU and Akerne fertilyser (to say in another way: too much K in comparison with nitrogen content).At these conditions I have observed very hard leaves on Phalaenopsis hybrids and leaves crooked and freeing itself hardly of their envelope for Masdevallias.

 

[Rick]

I've been feeding at 5ppm N and not seeing problems with over hard leaves. I'm just not finding any justification to apply nitrogen (via nitrate or ammonia) at concentrations over 5-10ppm for masdevalias. Even if Ca is 10-15 ppm with N down to 5 ppm seems fine.

Compared to high K results my plant leaves have much harder/ firmer substance (including Phaleanopsis) as tissue Ca increases. This seems to deter mealy and scale bug problems. I am not seeing leaf crippling in the pleurothalids that I can attribute to Ca overdose.

 

[Brabantia]

Rick: at which frequency do you feed at 5 ppm N?

 

[Rick]

Rick: at which frequency do you feed at 5 ppm N?

Daily to every other day.

 

[Rick]

For clarification Brabantia:

MSU pure water 13-3-15 8Ca 2Mg
K lite 12-1-1 10Ca 3 Mg
Akern rain 13-3-15 11Ca 3Mg

They are almost all the same as far as N to Ca/Mg goes, and actually the old MSU pure water has the least Ca compared to N.

If the question was adding even more Ca and Mg (either by pot ammendments or to the feed) was detrimental to Pleurothalids when using these feeds, I would generally agree. In fact I see no reason to use supplemental Ca/Mg for any orchid with these feeds either in the feed or in the potting mix.

I have found lately that some additonal P and Mg has helped green plants up where calcerious pot supplements seem to be causing yellowing with K lite use.

 

[Brabantia]

Daily to every other day.

5 ppm N daily ... is it the same as 30 ppm per week? Do you use an inert (mineral) substrate?

 

[Rick]

5 ppm N daily ... is it the same as 30 ppm per week? Do you use an inert (mineral) substrate?

If you don't consider how much gets held up (or flushed out) in the media you are correct.

My mixes do use considerable large limestone chips, which are probably more inert than LECA. I also have a lot of mounted plants which offer very low storage volume to surface ratios compared to potted media conditions. Consider the amount of K held up in various media data that Xavier presented.


All media held up considerable K over the year or two of application. Despite all getting fed the same rate,the Orchiata bark stored the lowest, while I think sphagnum stored the most.

So I think by frequent very dilute feedings (rather than periodic heavy feedings) the equilibrium will ultimately favor much lower total exposure of nutrient, and a more favorable diversity of microflora.

 

[Stone]

5 ppm N daily ... is it the same as 30 ppm per week? Do you use an inert (mineral) substrate?

It might be more accurate to say ''whenever you water'' or ''every second watering'' etc. So if you have determined the optimum fert rate for every watering, you need to double that for every second watering and quadruple for every forth watering.
But the longer you leave between feeding the greater the risk of too high salinity. So I agree with Rick that more often but weaker is probably best. But I would add that you still need to flush well from time to time. Large volumes of water 3 times but 2 hours apart ( to allow time for everything to go back into solution) would be good and you can feed again straight after that if you want to bring the EC back to where you want it.

 

[Ray]

I think that media play a role in our feeding regimen, but sort-of in a "converse" role to what most folks think (because they're used to terrestrials in soil).

In my opinion, most orchid media do not contribute appreciably to the plants' nutrient supply. However, they can sequester nutrients, throwing off the "balance" we think we have achieved. Then, over time, they become so saturated with those minerals and waste products that they are the veritable overfilled-balloon, and - ka-pow! - dump them back into the environment at outrageous concentrations.

That would imply that a totally inert, open and non-absorbent medium, coupled with very frequent, diluted fertilizers solutions, would be the ideal.

Maybe it's time for some additional experimentation. Marbles? Ceramic ball-milling media?

 

[Rick]

Maybe it's time for some additional experimentation. Marbles? Ceramic ball-milling media?

Yes, marbles would be about as inert as you can get. Or trying full hydro?

I was remembering our threads with RB down in Florida with her Catts and Hoyas, and how she was ramping everything up to offset nutrient deficiencies (?!?!).

I recently got some hoya stem cuttings and stuck them in cups of my well water. No media, no feeding. In 3 months getting fantastic root growth and one cutting is now in bud!

 

[terryros]

I always think that these full hydro stories with orchids tell us that it isn't roots being too wet in sphagnum (or other substances) that is a problem. It must be something wrong with the chemical balance that causes problems with the roots, like becoming too acidic in sphagnum. I don't hear that people are doing anything special to get oxygen to the roots in these hydro setups, either. Is there any oxygen uptake at the root zone or is all gas exchange through leaf stomata?

Perhaps having the right EC, pH, and nutrient balance in the surrounding fluid is what is most important for the roots.


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[Rick]

Perhaps having the right EC, pH, and nutrient balance in the surrounding fluid is what is most important for the roots.


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That's exactly what I've been thinking.

I recently saw a hydroponic system that keeps O2 high at the roots. The plants are suspended over a tank of hydroponic solution that has a pump and spray bar on a timer. Depending on how you set the timer, the roots are sprayed periodically, but in generaly they just hang over the nutrient tank.

How different is that from my mounted plants that I spray every day? My vandas aren't even on mounts, just a basket with bare roots hanging down. I spray almost daily with a nutrient solution EC strength of 50 to 100uS, and I've never done better!!

 

[Stone]

That would imply that a totally inert, open and non-absorbent medium, coupled with very frequent, diluted fertilizers solutions, would be the ideal.

I think a totally non absobant material may be too difficult to manage long term.
If all factors were kept in perfect balance that may be ideal, but for me, I still prefer some sort of high Cation exchange capacity material such as moss or some kind of humus incorporated into the mix as a nutrient buffer. Some of the material which our favorite paphs grow in (especially the rock crack dwellers) seem to grow in a very fine material made up of very old humus and disolved clay etc and this must have a high CEC. I seems to me these types must rely more on disolved nutrients soaking into the humus pad with rain water rather than a freaquent litter replenishment. It may also be the reason why a lot of these species seem to resent root diturbance. Now if we can come up with an inert media and some sort of long lasting humus type material so we can leave them in the same pot for years we should be on the right track. Planting them in mossy, leafy, barky mixes will work for a time but when the plant is repotted, it is set back. Maybe with big chunks of zeolite you could have more success with totally inert media for the brachys etc.
But I think the barbata types like frequent repotting into fresh organic media.

 

[Ray]

My only concern with marbles is that soda-lime glass can be pretty alkaline. Probably not really an issue with such small surface area, unlike Growstones.

I DO know that glass is leachable though. Water reacts with the alkaline elements - Na, for example, forming NaOH that dissolved the silica structure, releasing everything.

It is a really slow process though - I have a prohibition-era whiskey bottle recovered from Long Island Sound by a scuba-diving friend, and it is iridescent, courtesy of the undermining of the surface by that chemical process.

So I guess that means that marbles would not be a good choice after the first 70 or 80 years.

 

[Stone]

So I guess that means that marbles would not be a good choice after the first 70 or 80 years.[/

Yes after that you would need to re-think it.

 

[ALToronto]

Ray, such leaching is unlikely to happen since most fertilizers turn the water slightly acidic. Glass is ok up to a pH of 10 or so (unless it's Pyrex, then it can't handle any alkalinity). But even Pyrex is unlikely to disintegrate in our lifetime, or raise the pH enough for orchids to notice. I also suspect that glass-making technology has improved somewhat since that whiskey bottle was made.