Just in a hurry, it is working time nonstop...
A little bit Paul.
A bit later it says that toxicity is not an issue (with relation to potting mixes/feeding), apparently not feeling that nutrients can cause "toxicity" by definition.
Absolutely, because I have seen only few cases of true toxicity, proven by leaf analysis, which would mean the analysis result exceed the norms. So far sodium, boron, manganese ( in one US bark source) come to mind.
As for potassium, the figures from the wild and from culture are pretty constant, and nowhere near any toxicity. There are no documented cases of potassium toxicity in any lab that processed analysis of orchids. So we cannot speak about toxicity. Deficiencies are plentiful, on the other side.
Now, an IMBALANCE would be something different, which means there is a lack somewhere else of something else, which would make the plant sick.
One example would be nitrate. Nitrate can be highly toxic to the plants in minute amounts if the plant lacks molybdenum. Even 20ppm of nitrate in the feeding can make a chlorosis becomes much more severe if the plants is lacking molybdenum.
The same, if the plant is deprived of any iron, manganese, zinc and copper, with no supplementation at all, even 0.1ppm of iron will induce a very severe chlorosis and necrosis. it is not 'iron toxicity', it is in fact the imbalance of iron, zinc, manganese and copper together.
He mentions the low K feeding as a US phenomena, but really doesn't get the reasoning correct. He neither critiques it as significant or not.
I have on hand the analysis of quite a lot of growers, some pristine ones for even pot plant phalaenopsis, and so far there has never been any potassium toxicity ever reported, in terms of quantity in the analysis. So for me, potassium toxicity might exist possibly, but it has never been found, and in fact for the low K fertilizer, that would be interesting to have true foliar analysis, etc... to see if there is really a potassium toxicity problem, which would be unheard of.
I would be more scared by a potassium deficiency, because it is a sudden collapse of the plant, and once the potassium is moved out of the old tissues, there is no way to restore older plant parts content when they are too old ( 2-3 years old), which means one could loose many old bulbs at once.
Now, and that's another point, there are couples, like potassium/sodium or calcium/magnesium, and if there is an imbalance ( let's say the calcium:magnesium in the leaves is at a 1:1 ratio), then that's a mess.
Then his new feeding regime is a hybrid of his old (high K feeding) and a new low K system. "Every 3 months I use a simple tank mix of 300mg of calcium nitrate and 200mg ammonium nitrate, with 5mg of boric acid as a drench". Although he insists its not to get any more calcium and less potassium into the plants.
Not at all a low K system in fact, I use the tank mix once every 3 months, so once every 50 waterings, it's negligible. It is not a low k formulation, but the combination of those three is required to supplement boron without any local phytotoxicity risk, the calcium + boron is safe on the new tender growth, and the ammonium nitrate is there to avoid a pH increase from the calcium nitrate. It is a proven way to supplement boron safely.
So far it does not get any less potassium in the plants, I use 49 times the standard feeding scheme, and once the boron, let's say it is negligible.
He still likes a lot of urea/ammonia, and is heavily invested in a calcium/boron theory (micronutrients in general). (although I will agree that calcium metabolism in virtually all organisms is partially linked to boron). Given some of the high alkalinity waters available to his growing conditions it could work for him.
I do not like a lot of urea and ammonium, but the plant do. If you ask Floricultura ( and they have plants that are 20-30 years old, motherplants, including quite a lot of species...), they still like it. The phals growers, all the successful ones use ammonium and urea ( and none is using the MSU).
The same for the MSU or high calcium and magnesium fertilizer, many careful studies ( one of the most extensive being the 1996 Van Os Onzekadezoenk study, commanded and paid by Floricultura, but there has been several since) showed that the growth was greatly reduced with the use of all nitrate fertilizer, or even calcium nitrate at too high strength.
And so far again, there has been a very big trial in NZ, with many different potting mixes and MSU was tried against a standard Peters 20-20-20, and MSU gave really bad results, using RO Water... The publication of the full trial should occur ( in an University publication) this year, but it was interesting really.
I use RO water, using an industrial RO water system, and the EC is between 8-12 microsiemens after filtration.
For the boron, it is not a theory, but unfortunately it is proven in some situations. After a while, many paphs (and phals...) growers said that 'the plants stop growing because the media is old'. Well, OK, so there must be something in the old media. Analysis after analysis, there were some differences, but nothing that could explain the root growth slow down after some months/a year. And nothing toxic. The only difference was boron, simple... Again, we could not find any of those 'salts accumulation that makes the media to become toxic' when the plants stop growing, except in specific circumstances ( tap water, not flushing properly, etc...), but there were some deficiencies, copper, boron, zinc... apart from some decayed media whose pH was out of range for the crop, of course.
From my experience in growing plants over the years, and apart from some of Xavier's more ''unusual references'', I would agree with most of what he says. Except the pH quote of 5.7-6 is a bit narrow to me. I would say 5.7 to 6.8 would be quite workable for most species. I also agree with the 50/50 nitrate/ammonium N for orchids if not all plants when specific species data is unavailable.
For the pH, 5.7 to 6.8 could be way too much for some species. In fact, we do not know the perfect specifics of all individual orchid species, but things like pansies, pelargonium, etc... have a pH range that is very narrow ( around 0.2 to 0.3 unit, not more), therefore my recommendation.