Paph. liemianum 'Charlie'

[Rick]

Also, now according to Rick's findings, a little calcium in the mix helps as well as increased Magnesium (epsom salts). I've known this about Brachy's and certain Phrags (especially besseae). When they are prone to rot, if you add some limestone screenings or feed with a high calcium fertilizer and suplement with epsom salts, rot becomes much less of an issue. What I didn't know is that it's the ratio of Calcium and Magnesium to Potassium that is important, not the total Ca and Mg alone. Too little Ca and Mg and too much K will encourage rot. Reverse this and rot is discouraged.

To modify this partially, the ratio is important, but reducing the overall amount of K is probably more so.

I have another paper on tropical epiphytes (based on bromiliads but applied to all epiphytes, orchids ferns...) that indicates that these plants are extremely efficient at pulling K from the environment. Actually all the papers I've dug up indicate that all plants selectively pick up K efficiently, but the epiphyte paper was the most detailed for something including orchids on that level of physiology.

So If you give lots of K they will selectively pull it out of the environment almost regardless of how much Ca and Mg is laying around.

A paper I have on Wild rice physiology indicates a similar effect. Even with excess Ca and Mg in the environment, the more K offered, the more K picked up by the plant, and blocks uptake of Ca/Mg. When environmental K gets high enough (sequestered in old potting mix for hobby orchids), the blocking effect on Ca/Mg also inhibits the uptake of P.

All natural surface and ground waters have a little potassium in them, and any organic potting material has K in it too. Given the efficiency of K uptake of orchids there really is no need to add any K by fertilizer.

 

[John M]

Thanks for the clarification on what I said, Rick. So, I'm taking from all this that my use of 7-11-27 really should be stopped and I should find a feed with a LOT less K...making it the smallest number, not the largest - correct?

 

[SlipperKing]

That's correct John and finding a suitable fertilizer with very little to no K is a nightmare if you want a nitrogen source other then urea!

 

[Rick]

Thanks for the clarification on what I said, Rick. So, I'm taking from all this that my use of 7-11-27 really should be stopped and I should find a feed with a LOT less K...making it the smallest number, not the largest - correct?

Yup of the NPK trio. But so far I don't have that much opinion on having phosphate higher or lower than K.

If your water has low alkalinity you could probably just use a dash of calcium nitrate and Epsom salt now and then. Maybe a dash of bone meal (CaPO4) in the potting mix. Late winter early spring a drop or two of Protekt (It has 0-0-3 NPK, but a 2 or 3X the silicon).

So far I've dropped my MSU use to 1/4 the recommended rate of 1/2 tsp per gal. That effectively turns it into a 3-1.5-3 mix. But a 1/4 tsp per gal of calnitrate should put the N back up around 9 (equiv), and Ca should be higher than 6 at that point.

 

[Brian Monk]

Loverly!!! Good luck with the propagation