What is the best fertiliser NPK?

[Ray]

If you look at orchid nutrition textbooks, you'll see a great deal of information, but it mostly pertains to food crops, and when ornamentals are brought into the discussion, there is very little info on orchids.

While I will not state that potassium is unimportant, I don't buy they contention that "all plants use about the same level of N and K". For one, the books show that the relative demand for specific nutrient elements varies all over the map. Tissue analysis, while not my favorite technique (what's in something doesn't necessarily mean it is what's needed), may be as good as we can get, and many show the K content to be no more than 10% of the N content.

If you look at the analysis of the solutions reaching orchids in the wild - cascading through the canopy and trickling down the trunks and branches, you'll find that 1) it's VERY dilute, at about 15-25 ppm TDS, and 2) the huge majority of that is nitrogen.

While looking at a textbook to see if I was remembering that correctly, I ran across something I hadn't caught previously - that for the most part, potassium is not metabolized within a plant, but stays in solution where it may loosely form complexes to achieve a specific function, then pop off for another use elsewhere within the plant. If you consider the water-conserving adaptations that many orchids - epiphytes in general, I suppose - have evolved, that supports the concept that there is less need to replace soluble ions.

[Orchid Whisperer]

Originally Posted by Ray

If you look at orchid nutrition textbooks, you'll see a great deal of information, but it mostly pertains to food crops, and when ornamentals are brought into the discussion, there is very little info on orchids.

While I will not state that potassium is unimportant, I don't buy they contention that "all plants use about the same level of N and K". For one, the books show that the relative demand for specific nutrient elements varies all over the map. Tissue analysis, while not my favorite technique (what's in something doesn't necessarily mean it is what's needed), may be as good as we can get, and many show the K content to be no more than 10% of the N content.

If you look at the analysis of the solutions reaching orchids in the wild - cascading through the canopy and trickling down the trunks and branches, you'll find that 1) it's VERY dilute, at about 15-25 ppm TDS, and 2) the huge majority of that is nitrogen.

While looking at a textbook to see if I was remembering that correctly, I ran across something I hadn't caught previously - that for the most part, potassium is not metabolized within a plant, but stays in solution where it may loosely form complexes to achieve a specific function, then pop off for another use elsewhere within the plant. If you consider the water-conserving adaptations that many orchids - epiphytes in general, I suppose - have evolved, that supports the concept that there is less need to replace soluble ions.

Baloney.

Ray, I have posted and re-posted in other threads research that shows, in fertilizer trials with Dendrobiums, and tissue nutrient analysis of orchids, that the ratios where N more-or-less equals K, and P is much lower, match the nutrient needs of orchids. It has been a few years since I have posted any of that I will see if I can find that research, and try posting it again.

The jungle trunk flow argument is just silly. What orchid grower would put up with the reduced blooming performance of an epiphytic orchid grown with the minimal nutrition available in the wild? Those plants often must reach a very large mass to store enough be able to bloom, hardly what the hobby grower wants. Research shows that while plants can bloom with less than adequate nutrition, they bloom better with proper nutrition.

I've spoken with my horticulturalist friend about the low K nutrient idea, to be polite, he thinks it's rubbish. He is also an extremely successful orchid grower, who adheres to N and K being co-equal nutrients in fertilizer. My money's on him.

[Ray]

You and he may think it's rubbish, or more of a "fertilizer" animal byproduct, but there are a bunch of us having great success with the technique, so "poo-pooing" it based upon a few articles is foolish and narrow-minded. Bumble bees aren't supposed to be able to fly, either.

I agree totally that we would not want to employ techniques leading to reduced performance in our plants, but the "trunk flow" concept gives us an idea of relative nutrient chemistry the plants have evolved to survive with, but certainly not that it is the proper availability.

And yes, maybe those dendrobiums have K = N in their tissues, but why does that necessarily mean that their food supply must have that same ratio? Do they use them at the same rate? Might the K just be stored in higher amounts? And why must the case with one plant have a bearing on whether that is the case in all orchids?

I think what this all boils down to is one camp in which folks are willing to accept what has already been described, and another in which more experimentation is done to test those concepts and others.

Quoting from Marschner, who literally wrote the book on Mineral Nutrition of Higher Plants, "Mineral nutrition of plants is under genetic control. In crop plants this is indicated by the numerous examples of nutrition differences between cultivars or strains."

[SouthPark]

In the 'wild', the orchids generally get relatively weak amounts of fertiliser when they're hanging on rocks etc. But for the case of orchids in nurseries etc, the amount of fertiliser they get is definitely a lot more than what they get in the wild, right? So the orchids are getting a lot better than what they get in the wild in general.

So - as long as the orchids being cared for do well - growing and blooming etc, then that's great already. Just like 'traditional' medicine - some very effective techniques have arisen by a combination of trial and error and experimentation - not necessarily with some science component involved...... even though some may have. When science does become adequately involved - and provided we have the means to work towards understanding things in a scientific way, then that is certainly a benefit.

I think that the main thing is - use whatever works well - which also means working nicely on a long term basis. And if not understood properly, then hopefully work may be done in future to understand it more.