Sodium Metasilicate vs. Potassium Silicate

demolitron(8)September 23, 2009

I was wondering if anyone would provide their thoughts regarding sources of Si for plants. I have been able to find two different chemical means. The first, and most popular it seems, is Potassium Silicate and the other is Sodium Silicate. I am discussing this in the context of container soil-less culture and continuous low level fertigation.

From what I have been able to find out, Sodium Silicate will work as a source of Silicon but it also contains appreciable Sodium. The chemical formula for Sodium Metasilicate Pentahydrate is Na2SiO3-5(H2O). Working out the molecular weight gives 13.23% Si and 21.67% Na. So it would appear that the downside to using it is the excess of Sodium you would be adding to the nutrient mix.

However, I have seen various articles relating the possibility that Sodium addition to Tomato plants increases the flavor and texture of the fruit along with an overall decrease in fruit size and quantity. From a commercial perspective that would be bad but from a home gardener's perspective I could live with slightly reduced yield in favor of better quality.

Now with Potassium Silicate (K2O3Si) you get 50% K and 18% Si. You can deal with the Potassium by adjusting your fertilizer mix to keep the nutrient levels wherever you want them. In addition I've read the Potassium Silicate is easier to dissolve in water and has less efflorescence.

So from these perspectives I would say that Potassium Silicate is the best substance to use. But one can get a gallon of 40% Sodium Silicate for $21 shipped. The lowest cost source I've found for Potassium Silicate is $25 per gallon of 15% solution, then add in crazy S/H fees. Overall, once I account for the different levels of Silicon content, I figure that Potassium Silicate costs 3X that of Sodium Silicate.

If the presence of Sodium can be tolerated, does anyone have a reason that Potassium Silicate should be used over Sodium Silicate? How much sodium can be tolerated by Tomatoes?

Here is a link to an interesting paper regarding Silicon and plant nutrition:

Thank you for your time.

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I use Potassium Silicate (DynaGro ProTekt) which suits my needs fine, but the sodium issue can be dealt with if you are using a free draining media and always water to run off.

Personally I think I would prefer the lower level of unnecessary salts, but if it's more cost effective to go the other route and you take the potential issues into account, why not?

I have no idea if additional sodium improves the flavor of tomatos or not. Over the years I have heard a zillion different ideas for influencing tomato flavor, virtually all with no basis in reality. If it does perhaps it does so by limiting water uptake due to excess salinity in the root zone resulting in less watery tomatos? Would seem like flirting with blossom end rot to me if that's what it does, but to each their own ;)

Just my thoughts, I haven't ever considered a source of silicon other than ProTekt.

    Bookmark   September 23, 2009 at 8:30PM
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Thanks for the response. My city water supply here has 90ppm sodium in it and it seems to be alright for my existing tomatoes. I am going to be using an RO water supply here pretty soon so if I add back in 90ppm sodium using sodium silicate I should be fine.

Thanks again.

    Bookmark   September 24, 2009 at 4:17PM
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