Confused about Potassium

[dshallpost]

I am confused about potassium and would love to hear your experiences and thoughts.

I understand that Potassium is one of the three "macro nutrients" (nitrogen and phosphorus being the other two) and that Potassium (K) is important for blooming.

Recently read the "Slipper Talk" article that describes the research which led its author to feel that potassium sometimes, for some plants, can lead to problems. Sometimes the plants do quite well and bloom well, and then give out after a few years.

This led to the development of the "K-Lite" formula. From what I have read, some people have had great success and others -- not so much, to the extent that they abandoned the reduced -K formula.

OK, so, confused already, I read an article by Martin Motes (the "October" entry in this month in your . . . .) I found my way to this article because I had received (from Motes) three vanadaceous plants that arrived very, very purple. Bart told me that it was caused by cold leading to magnesium deficiency. So I read up and found the article that his father authored describing using Epsom Salts. But -- here's where my confusion really peaked -- he recommended adding in Potassium Nitrate with the Epsom Salts.

I will share my confused journey with you thus far. My orchids were doing so-so and I decided to use a couple of humidifiers -- which really helped. These are hot, not cold, and that was fine; everything was working well. But we have moderately hard water and every week the level of accumulated salts in the humidifiers was appalling. I decided we needed a whole house softener, and very shortly after completing the installation, I learned that the sodium that gets substituted in the softening process for the minerals in my water would kill my plants! Discovered this just in time -- hauled the sodium salts back to the store, and bought potassium (at about 4x the price). OK, I thought everything is fine, and orchids like potassium right?

Well, now I am embarrassed to ask my husband, (who at my request, installed the softener, and hauled the salts) to install a bypass so that I can have a spigot in the house that will give me the original hard water --just for the orchids. (We use the unsoftened water for the garden too)

Are you laughing yet?

Is anyone else as confused as I am? or hopefully, armed with experience and recommendations that you would be willing to share?

[Ray]

Plant nutrition is a very complex subject, is not very well understood, and very little is known about orchid nutrition, specifically.

What I DO know is this:

1) Orchids have very meager nutritional needs, primarily due to their slow growth.

2) If you do a chemical analysis of plant tissues (which is still suspect, but better than no info at all), 95% is water. 95% of the "dry matter" is carbon oxygen, and nitrogen, and that remaining small percentage is everything else, combined.

3) If you look at the chemical reactions that occur within plants to assimilate carbon ("grow"), in order to add about one kilogram of mass - 45 days or so for corn, a few years for a cattleya, and a lifetime for a pleurothallid - they have to absorb and chemically process about 100 liters of water, and only about 5 grams of fertilizer nutrients.

If you look up an article Sue Bottom wrote on calcium deficiencies for the AOS Orchids magazine a few months ago, there is discussion about the accumulation of K & P being part of the issue, and that is actually part of how the K-Lite formula came into being. The original concept came out of a discussion between a biologist who deals with toxicity in mollusks and a ceramic engineer who knew the potential negative roles of excess K on glass and ceramic systems, who both wondered about the impact on plants. Upon doing some research, it appeared there might be something to that, so the guy that invented the MSU formulas was consulted to derive the formula, and some testing began.

I have used it exclusively since late 2011, and my plants have grown and bloomed better than they ever have, in my 45+ years of growing.

Yes, there were a couple of testers who felt that their plants were reacting negatively to it, but I am skeptical, as 1) it is VERY difficult to diagnose nutrient deficiencies - an excess of one looks like a deficiency of another, or a deficiency of one looking just like a deficiency of another, among other convolutions, and 2) in my experience, it takes a long time for a true deficiency to rear its ugly head in these slow-growing plants (other than that of calcium, which is needed continuously), and some of the reported reactions were just too sudden.

[estación seca]

What does your tap water quality report look like from the water utility? pH? Total dissolved solids?

[Roberta]

Good point, ES... the water softener replaces the calcium with potassium, so how much is in the treated water is a function of how hard the water is. (Whatever ppm calcium you have, when it's replace by potassium, the ppm will be twice as much ... fundamental chemistry) If the hardness isn't too bad to start with, the potassium you are adding may not be that horrid. The dose makes the poison...

[estación seca]

Unless every other aspect of your growing area and watering habits is already perfect, don't bother worrying about fertilizer. Fertilizer composition is the least important factor in growing orchids.

[Orchid Whisperer]

Plant nutrition is quite well studied.

For virtually all plants, for the major N-P-K plant nutrients research indicates roughly equal need of N and K. Much less P is required (varies, but P at roughly 20 % of N and K). This is verified by plant tissue analysis of traditional row crops, and also plant tissue analysis specifically of orchids grown in horticulture. It has also been confirmed by scientific trials which varied ratios of N-P-K applied to cultivated orchids (Dendrobiums specifically) and examining the growth response; reducing N, or K, adversely affected growth and performance, while reducing P had only a slight negative response.

My orchid club includes plant scientists at the University of Georgia, experienced in growing orchids and other tropicals, including other epiphytes. They do not adhere to the low fertilizer K approach, and instead prefer balanced N and K and low P.

When considering fertilizer inputs, in addition to fertilizer, and water, you also need to factor in K and N that may be added by other supplements, such as Cal-mag supplements, kelp extracts, etc. Nutrients provided by these products may be significant, thus you may be able to apply less K in the fertilizer if you are also providing a kelp extract, or less N if you are applying calcium nitrate to provide Ca.

[dshallpost]

Thank you to all who responded! The perspectives were very helpful.

So of course, first -- assess your water! The unsoftened water has a PH of 7.2 and PPM of 141. The softened water has a PH of 7.2 and 139! Almost identical. I will need to assess again, with some nutrients added, to see if these lower the PH or whether I need to add something else (Tea bag?) to get to 5.5-6.5.

I think I will just finish out using some MSU tap water fertilizer that I already have been using (at half strength) with the unsoftened water. I will just continue to use unsoftened water for the orchids. Have also started using Epsom salt for the orchids with a deficiency. And occasionally adding in SuperThrive.

Will assess water again when fertilizer has been mixed in and if it is still to acidic, will try using a tea bag in the water -- does that sound about right?

Thank you again!!!

---------- Post added at 08:26 AM ---------- Previous post was at 08:22 AM ----------

I am still confused about potassium but I guess I am in good company there.

[Ray]

When we bought our house in PA, where our well water had a seasonally-changing pH of 3.7-4.2, potassium carbonate solution was injected to correct the pH and to prevent our pipes from disssolving (nobody in that house will ever die of a copper deficiency!). While I was "certain" it was no issue with my plants, I couldn't possibly use it for tropical fish.

A couple of years later, I purchased an RO system for the greenhouse, and only changing that, in a couple of months I saw a marked improvement in the plants; they all looked brighter and cleaner, and just healthier.

To answer the question about the role of potassium, while I cannot give specific chemical reactions or compounds, if there is too much potassium in the applied solution or even accumulated in the potting medium (which then helps saturate the solution), the K ions can occupy too great a percentage of the binding sites in the velamen, preventing other ions from being absorbed, and once absorbed, can bind with sites in the plant chemistry that other ions, particularly calcium, should occupy.

Sue Bottom (she is responsible for most of the great info at the St Augustine OS website) recently had an article on calcium deficiency punished in the AOS Orchids magazine, and in it she mentioned discussions with a prominent vanda grower on FL in which he mentioned K & P interference with Ca uptake, and referenced a supporting publication by Joseph Arditti, arguably one of the most knowledgeable orchid scientists out there. I wish I still had that issue...

Taking a look at orchids in nature, while it certainly varies all over the map (literally), the solutions that cascade onto the epiphytes in rain forests typically contain no more to 15-25 ppm dissolved solids, and the vast majority of that is nitrogen. The K and P contents are quite variable, but also quite low, lending some credence to the K-Lite concept.

I will agree, however, that fertilizer is WAY down the orchids' Maslow's hierarchy of needs. Unless your feeding regimen is way out of whack, fertilizer is never going to fix a problem with your plants.

[dshallpost]

Thanks for the pointer to St Augustine. Great information there!

[greenpassion]

And an answer to your problem about your humidifiers, use RO water. Or distilled water. I run two of them for my orchids all winter long and only need to clean them a little over once a week.