I hate it when people text me K; I’m very rarely in the mood to talk about Potassium via texting… I am, however, pleased to have a good chat about it now, along with Phosphorous because P and K are very good friends in the Hydroponics industry and it would be a shame to split them apart. We’ll start with Phosphorus…

Phosphorus is the 15th element on the periodic table with the symbol ‘P’. Due to its high reactivity Phosphorus is never found as a free element because it is highly reactive. Next time you check the back of a fertiliser bottle see what it has been combined with, you’ll usually find it’s combined with other elemental containing minerals. Some common Phosphorus combinations include Phosphorus pentoxide and monopotassium phosphate.

"In Latin, it means ‘Lucifer’"

The discovery of Phosphorus is credited to Hennig Brand, a German alchemist who attempted to create the fabled philosopher’s stone through distillation of some salts by evaporating urine. During this process he produced a white material that glowed in the dark and burned brilliantly, it was named Phosphorus mirabilis (Miracle bearer of light) and for those that love to geek out like me, the light emitted is called Cherenkov radiation. After its discovery, it was used as stage lighting during theatrical performances to light up the actors.
The first elemental Phosphorus produced was in 1669, this was white phosphorus which emits a faint white glow when exposed to Oxygen. The faint white glow is what actually gives Phosphorus its name, originating in Greek Mythology Phosphorus means ‘light bearer’. In Latin, it means ‘Lucifer’ in its reference to the morning star (Venus and sometimes Mercury).
Although it is the 15th periodic element, it was the 13th element to be discovered. It is perhaps for this reason that it is called the devils element, or perhaps it’s because of its use in explosives and nerve agents for some of the most despicable acts known to man.
However, Phosphorus is essential to life, phosphates (compounds containing the phosphate ion PO43-) are components of DNA, RNA and ATP along with phospholipids which form all cell membranes.
This importance shows in the hydroponics industry with the abundance of Phosphorus containing products in every shop in every country. Here’s how to spot deficiencies and over fertilisation with Phosphorus…
Deficiencies will manifest themselves through slow growing, weak and stunted plants, these can be dark green in colour with the older, lower leaves showing possible purple pigmentation. As Phosphorus ions are fairly mobile, Phosphorus deficiencies will initially occur in the older leaves. This is due to the necrotic tissue (dead patches), reddening of stems and poor rooting.
Toxicity will show mainly in the form of a micronutrient deficiency, with either Iron or Zinc being the first elements to be affected due to the interaction of Phosphorus ‘out-competing’ other elements.

A ‘What is…’ article usually focuses on the individual elements, but because Phosphorus and Potassium are always found together in the PK boosting products, we’d like to include Potassium in this article of ‘What is (are)…’.

Potassium is a chemical element with the symbol K, from the neo-Latin ‘Kalium’ and has the atomic number 19. You may remember it as the soft silvery metal that reacted vigorously with water in school, I remember it as the silvery metal that destroyed the school’s toilet when we decided we wanted to see what a bigger piece of potassium did… The chemistry teacher was impressed, the headmaster not so much. The equation for that toilet water reaction was as follows;
2K + 2H20  2KOH +H2
It was first isolated from Potash (the ashes of plants) and is where it also gets its name. Humphrey Davy was the scientist that is credited with finding Potassium in 1807 from caustic potash (KOH – Potassium hydroxide).
Potassium is involved in maintaining the water regulation of the plant, the turgor pressure of its cells and the opening closing of its stomata. It is also required for the accumulation and translocation of newly formed carbohydrates.
If your plants become Potassium deficient they become sensitive to disease infestation and fruit yield/quality will be reduced. Older leaves will look as though they have been burned along the edges, a deficiency known as scorch, because Potassium is mobile in plants.
If you add too much potassium, the plant will become deficient in Magnesium and possibly Calcium due to this imbalance, with Magnesium deficiency likely to occur first. There are good arguments for the use of a Calcium/Magnesium supplement during flowering periods of heavy PK use. We will be looking at this in more detail with Garden Culture’s next edition of ‘What is (are) Calcium and Magnesium’.
There are two topics that you might think we’ve missed in this article of ‘What is…’, the relationship of P and K in flowering additives and the impending Phosphorus crisis. Both topics require an article by themselves so that gives you something to look forward to or fall asleep to…

Thank you for taking the time to learn a little more about Phosphorus and Potassium, before I go here’s one to finish.

Did you hear about the time Oxygen and Potassium went on a date? It went OK… No more, I promise.