Since silicon is the second most abundant element on the earth's surface - only oxygen is more abundant - and mostly in the form of silicates, it's difficult to understand why it would ever be necessary to supplement.

What about potted trees?

I think the silica "hype" started with hydroponics, where I would think it's useful since there is no soil involved.

I garden in pots only, and I do give my plants (and potted trees) a liquid silic additive, since there is no actual soil in my potting mix.

If gardening in the ground, or if you are mixing garden soil into your potting mix (I don't, but I know several people who do) then I would think it's not useful since the soil would provide it.

Maybe I've just fallen prey to hype. I have been noticing thicker stems and leaves since I started using it, but as they say, correlation is not necessarily causation.

It's not a necessary plant nutrient and the literature seems to indicate that its primary claim to fame involves the amelioration of abiotic stress. Since abiotic stress is far easier to manage under a container gardening scenario than in the ground, I still don't see any big advantage to adding. But then I am highly skeptical about adding any dubious, not well-supported by science stuff to a container planting situation. IME, most do more harm than any good. Or you are paying through the nose for really nothing much at all.

Silicon is like Ca in that it must be in the nutrient stream at all times if it is to be effective, so it requires dedication to a program centered on not allowing it to be depleted from the soil/ soil solution.

Horsetail reed (Equisetum hyemale) is also called scour or scouring rush because pioneers heading west along the various trails would seek it out and put it to work when scouring their cooking utensils. The reason it is stiff and abrasive is the high % of silicon it contains. Regular and consistent use of products containing silicon in a form plants can take up provides many benefits to a high % of plants. I'll try not to make this sound like a commercial, but much work has been done to identify and link the following advantages to regular supplementation of silicon, especially in containers:

Since it hardens cell walls and makes them more rigid, it makes it more difficult for insects and disease pathogens to breach cell walls. Silicon is known to improve growth rates and yields of food/ greenhouse/ nursery crops, help limit lodging, a plant's tendency to lay over due to weak stems - common in low light, indoor conditions. It helps keep plants growing upright, and the stiffness it adds helps keep leaves oriented to the sun in more advantageous positions. I already mentioned it increases a plants natural defenses against disease pathogens and insect herbivory, and helps the plant better tolerate stressors high salinity, high temps, low moisture levels, and aluminum toxicity.

I have used it regularly, and have noticed improvement in most plants, particularly in the foliage - thicker leaves that have a stiffer look and feel to them, and plants seem to better handle the high dog days temps that kill a lot of roots and lead to an increase in root rot showing up in the fall. Unfortunately, I have too many plants, which disallows me from doting on them as I would if I had the time, and the industriousness of years gone. That means the program I initially started degenerated into a hit and miss sort of thing that either nullified silicon's benefits or made them inconspicuous ..... but that's on me.

Al

>>Silicon, often referred to as Silica,

Right away I am suspicious these folks aren't that smart technically speaking. Silicon is the element, Si. Silica is crystalline silicon oxide, [SiO2}n.

Small error? Maybe, but if the topic is so important, at least get the names and definitions right.