No Silicon on the list, and yet from an LSU article on Silica and Rice Growth, we can see that up to 8% of rice straw is ... Silicon. Now it's not exactly breaking news that plant's use Silicon. As early as 1867 German scientists suspected it helped prevent grains from lodging. In his 1993 article, The anomaly of silicon in plant biology, Emanuel Epstein notes there are clear benefits to Si, but wrestles with the idea of being able to define it as "essential".
The problem with the term "essential" that it is possible to grow plants to maturity in mediums where Silicon has been completely excluded. The catch though is that these plants are rather pathetic compared to plants that have access to Silicon. As Epstein writes in his 1999 paper aptly titled, Silicon,
"[Silicon deprived plants] are often structurally weaker than silicon-replete plants, abnormal in growth, development, viability, and reproduction, more susceptible to such abiotic stresses as metal toxicities, and easier prey to disease organisms and to herbivores ranging from phytophagous insects to mammals."
So although Silicon is not essential for some plants in that they can conceivably live without it in a laboratory, it is possible these plants would not survive environmental stresses in their natural habitat without Silicon. Adding further confusion to the "essential" debate is the fact that "for certain algae, including prominently the diatoms, and the Equisetaceae " Silicon is indeed an essential nutrient, without which these plants would not grow. By 2005, Epstein and Bloom settle on the term "quasi - essential"
The takeaway from all of this is that although semantics prevent Silicon from being defined as an essential plant nutrient, it's safe to say it's rather important for a healthy plant. It's benefits range from greater resistance to drought and pest stress to stronger cell walls (which is what helps prevent the lodging those Germans were talking about). The proof is in the pudding of course so here are some pictures from Janislampi's 2012 paper, Effect of Silicon on Plant Growth and Drought
Stress Tolerance. Check out the artilce for more pictures.
And although the world of plant nutrition may not have fully embraced silicon's importance, cannabis nutrient companies are all over it.
In time I think the table of essential plant nutrients from the very beginning of this post will be but a relic. Until then, don't forget to give Silicon the credit it's due!