# Silica



## RNCollins (Jul 12, 2014)

I got a few samples from Botanicare and one of them was *Silica Blast.*
It is 2% Silica derived from sodium silicate and potassium silicate (0.5% Soluble Potash K20).

It says it will help strengthen plant tissue to flourish in adverse environmental conditions such as heat, drought, and frost.

http://www.botanicare.com/Silica-Blasttrade-P53.aspx

Does anyone have any experience using Silica? What are your thoughts about using Silica?


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## Ray (Jul 12, 2014)

Dyna-Gro Pro-teKt is a potassium silicate solution as well. It is marvelous for raising the pH of overly-acidic solutions (I used it for that when using Dyna-Gro "Grow" in RO - without it the pH was in the upper-3's/low-4's).

Advertising claims I have read are that it builds up cell walls, making them less likely for insect damage, and makes plants more heat resistant.

My own experience tells me it doesn't add anything to the well-being of my plants, and as someone using K-Lite, I'd avoid it.

Silicon is especially important in the diets of sugar cane and grains, especially wetlands type such as rice; most other soil-grown crops will absorb it because it is the second most abundant element on earth. There is no documented evidence of silicon deficiencies in most plants, and I seriously doubt that an epiphytic orchid would ever see much at all, if any.


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## PaphMadMan (Jul 12, 2014)

A product like this can be important in a hydroponic grow system because the plants get only what you give them, and most plants will take up silica and incorporate it in support tissues. Some care must be taken in using it because it is sensitive to pH and concentration, something hydroponic or commercial growers have to deal with but you usually don't to the same extent. And your orchids almost certainly have silica available to them in your potting mix already, and as Ray pointed out, they don't come from an environment particularly rich in silica. 

Silica is the most abundant material in the Earth's crust, and almost every kind of rock except most limestone/marble is made up mostly of silica based minerals. Perlite, rockwool, lava rock, any kind of clay/ceramic pellets, and almost any kind of gravel that might be in your mix all supply silica. Also, silicon is one of the 10 most adundant elements in plant tissue on a dry weight basis, so bark, moss, charcoal etc. also supply silica. Coconut or bamboo based materials would be especially high in it. 

There would be no harm in using this type of product with reasonable care, but I doubt you would see any benefit. If you do want to try though, I would look for a product that does not contain sodium silicate, plants do not need sodium, and you should definitely be aware of how much potassium you are adding and possibly adjust your other fertilizers accordingly.


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## troy (Sep 10, 2014)

I got some silica called god cilica, was a sample, I used it and I sware the leaves on my plants are stiff shiny and thick, although it goes agianst the low potassium rule, it worked for me. my fertilizers are low in potassium. Really got to watch the spike in the ph


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## Stone (Sep 11, 2014)

PaphMadMan said:


> > Ray pointed out, they don't come from an environment particularly rich in silica.
> 
> 
> 
> ...


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## Bjorn (Sep 11, 2014)

In my daily work, I have come across this topic, and am currently involved in an international project dealing with use of silica in plant nutrition. Silica in plant nutrition is an old topic and some 100 years ago, it was regarded as an essential nutrient. And although its the most abundant material on earths crust, silica in available form is rather scarce. The solubility is low and it is unstable in the sense that the available isomorph tend to polymerise and thus gets unavailable for the plants. Good soil can typically contain 10-15ppm as available silica (monosilicious acid).

Plants can roughly be divided into two groups, those that are silica accumulating and those that are not accumulating. 
Some important crops that are accumulating are sugar-cane and rice, both of these crops benefit from silica nutrition if the soil is depleted - which may easily be the case. Alkali-silicates like Pro-Tekt are not commonly used in agriculture; on a large scale mostly slags from iron and steel production are used.
Most orchids are probably non-accumulating.

The effect of silica has been the focus of a lot of research during the last decade or so. Even if it hardly can be classifierd as an essential element, it does play a role, particularly for stressed plants. Plants that has sufficient silica supply will resist stresses better, be it salt, drought or pests, and will need less fertiliser for the same yield. Particular the utilisation of phosphorous seems to benefit.

The role of the silica in the defence against pests and fungii is manyfold. One of them is that it tend to strengthen the epidermis (the "skin") so that attaccing pests/fugii does not penetrate, another thing it does which is not that visible is to be an invaluable part of the plants immune system. When a plant is under stress, be it an attack from fungii or insects, it starts to produce signal compounds (eg salisylic acid) that trigger production of a range of chemicals whose aim is to suppress the origin of the stress. Silica plays an essential role in that sythesis and plants depleated in silica will have a reduced immune defence system.

Whether or not your orchids needs silica is difficult to assess, many water sources have sufficient dissolved silica already, while others like RO water definitely could be improved by some addition. I am not implying that silica addition is essential, but having enough dissolved silica available would probably improve plants resistance to stresses and could render your collection healthier. 

Stuff like Pro-Tekt is not that suited since it raises the pH (its silica dissolved in potassium hydroxides). Other sources are hard to get to for most people....Perhaps the best is to add Pro-Tekt and then acidify the mix?


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## Ray (Sep 11, 2014)

Stone said:


> PaphMadMan said:
> 
> 
> > Certainly any terrestrials would have abundant silica available to them. Epiphytes as well from rain etc.
> ...


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## troy (Sep 11, 2014)

I think using it once every few months would work, thats what I'm gonna do


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## gonewild (Sep 11, 2014)

troy said:


> I think using it once every few months would work, thats what I'm gonna do



I'm curious why you think once every few months would work?

IF orchids need or benefit from Silica then why would they not need it every day?


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## troy (Sep 11, 2014)

All my plants seem healthy enough, the cilica does have potassium in it and that mixed with my fertilizer even though it's low in potassium, I think would be too much, I don't want to overdo it


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## troy (Sep 11, 2014)

I have a 38 inch leaf paph that have very stiff and shiny leaves now after using that


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## gonewild (Sep 11, 2014)

troy said:


> I have a 38 inch leaf paph that have very stiff and shiny leaves now after using that



For how long have you been using it on the paph?


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## troy (Sep 11, 2014)

I got the paph ending of last month


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## troy (Sep 11, 2014)

Thats one of many that stiffened up, for me I'm gonna use it once every few months, partly because there is too many other variables, but I like using it once in a while


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## gonewild (Sep 11, 2014)

troy said:


> I got the paph ending of last month



Not likely in two or three weeks the plant has had time to use any silica.


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## gonewild (Sep 11, 2014)

troy said:


> but I like using it once in a while



OK, that's the best reason to use silica that I've heard yet.


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## Parryaw (Sep 11, 2014)

Is it the same as the silica used to reduce humidity for dry foods?


Sent from my iPhone using Tapatalk


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## Bjorn (Sep 11, 2014)

Lots of good misconceptions around here:evil:
The first one that silica is insolubleartly true, crystalline silica is insoluble more or less, but amorphous silica dissolves between 10 and 100ppm depending on temperature and pH. In good soil some 10-20ppm dissolved silica is present. In plant sap several thousand ppm has been found. The fact that most plants contain at least as much silica as potassium and phosphorous should also indicate that somehow the plants are capable of utilising the available silica.

Next that there is no silica available for epifytes. These plants also contain silica, so it must be present. My guess is that the dust that is carried by the trade winds are responsible for a lot of the silica supply, as it is for many other nutrient elements. Much of the fertilisation of the Amazonas comes from Sahara desert. Futher, bark contains silica in available form. Decaying bark should be available for epifytes if the dust is missing.

Recent research indicates that silicon in plants is translocatable, if a leaf gets under stress, silica is supplied from neighboring leaves. This is not understood but has been measured.

Mostly, the plants get sufficient silica, but the signs of too little are so vague that they mostly will be overlooked. Things like increased susceptibilty to pathogens can be caused by plenty of other reasons. 

I am uncertain whter things like pro-tekt is the solution to this, mostly due to the pH issue. If that gets corrected a supply of some 10ppm in the irrigation water would do no harm.

Good luck:rollhappy:


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## NYEric (Sep 11, 2014)

I stopped using Protekt because I went K-lite. I may start adding a little back to my Phrag trays.


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## Ray (Sep 11, 2014)

I think come of it is semantics, and some inconsistent use of terms.

"Silica" is SiO2 in the materials industry. To me, amorphous silica is pure silica glass, which is still highly insoluble in almost anything but HF.

So a question, Bjorn: do plants contain SiO2, or Si, which is incinerated and oxidized in the analytical lab? I can see the metal more than the oxide.


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## PaphMadMan (Sep 11, 2014)

Stone said:


> PaphMadMan said:
> 
> 
> > Certainly any terrestrials would have abundant silica available to them. Epiphytes as well from rain etc.
> ...


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## gonewild (Sep 11, 2014)

PaphMadMan said:


> Stone said:
> 
> 
> > I just want to make it clear that the above quote is NOT from me, though the quote function somehow seems to think it is.
> ...


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## AdamD (Sep 11, 2014)

So would DE contain silica in available form to the plant? Either foliage or roots?


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## gonewild (Sep 11, 2014)

AdamD said:


> So would DE contain silica in available form to the plant? Either foliage or roots?



If the silica in Diatoms were soluble it would not make them a very good exo-skelton since the lived in water. So answer must be, no.


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## AdamD (Sep 11, 2014)

So, I guess the follow-up would be, is potassium silicate the best available option? If pH were adjusted?


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## Stone (Sep 11, 2014)

Ray said:


> Stone said:
> 
> 
> > > And how wold silica get in rain?
> ...


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## Stone (Sep 11, 2014)

AdamD said:


> So would DE contain silica in available form to the plant? Either foliage or roots?



Yes.


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## Stone (Sep 11, 2014)

AdamD said:


> So, I guess the follow-up would be, is potassium silicate the best available option? If pH were adjusted?



There is (or was) a product in the US called ''Pyroclay'' which does not have all the negative qualities of Potassium silicate.
It is not available here but I try to regularly add silica to the plants in the form of ''diatomite water'' or from composted bamboo leaves and fibrous grasses etc. I have no idea if it makes a difference. Silica certainly makes a big difference with some crops. Stronger and taller flower stems in Gerbera, higher yeild and bigger root system in Strawberry etc. etc. etc.


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## troy (Sep 11, 2014)

Rain water washes down the hill through the trees and bushes over roots


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## ALToronto (Sep 12, 2014)

I use soluble silicates in the production of my mineral composites. The most common ones are sodium, potassium and lithium, but there are others (magnesium, titanium, zirconium, etc). The alkali component is the carrier for the silicate component.

These are generally referred to as metal silicates and are written as M2O:SiO2, where M is the metal (Na, K or Li). The most important property of metal silicates is the molar ratio of the M2O component to the SiO2 component, i.e. how many molecules of M2O there are for every molecule of SiO2. The higher the ratio, the less silicate it contains, and the higher the pH. Cost goes up dramatically as the ratio decreases.

Most industrial grade metal silicates have molar ratios between 2.0-3.5. These correspond to pH levels of 11-12. Lower ratio silicates are used in concrete production, higher ratio ones are put in laundry detergents and used in the oilfields. In prepared liquid products, the solids content is 25-30%, but you can buy crystals and dissolve them yourself. It takes a long time with continuous stirring to get even 30% solubility.

In spite of molar ratio being the important property, silicates are graded and sold by the weight ratio - molecular weight of M2O:SiO2. This is because the molar ratio of the most common liquid silicate, Sodium, is the same as its weight ratio. Potassium is heavier than Sodium, so the same weight ratio = lower molar ratio. Lithium is lighter, so you get a lot less SiO2 for the same weight ratio.

Which brings us to Pro-Tek, which has a molar ratio of 0.25. This is extremely low, and I don't even know who makes liquid silicates with such low ratios. Certainly not PQ Corporation, the world's biggest producer of soluble silicates. Pro-Tek is also very dilute, with 7% solids. Even so, it's a significant pH booster, so I can only imagine how much industrial liquid silicate will raise the pH. You will also be adding 8-12 times more hydroxide salts for the same amount of SiO2 added as with Pro-Tek.

I don't use Pro-Tek because my plants get silica from other sources. Those that grow on my living walls get plenty from the wall material and the chopped hemp stems I use for the surface layer. I have a few plants in pots, in lava rock, with hemp stems mixed in. Bark and CHC also contain soluble silica, and LECA doesn't. This might be why my plants growing in LECA are doing worse than the rest.


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## troy (Sep 12, 2014)

Thank you altoronto, very detailed explanation of the moleculuar breakdown of silica, yur an intellegent person, do you have a science degree? Protekt or such is nonsoluble


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## Bjorn (Sep 12, 2014)

Ray said:


> I think come of it is semantics, and some inconsistent use of terms.
> 
> "Silica" is SiO2 in the materials industry. To me, amorphous silica is pure silica glass, which is still highly insoluble in almost anything but HF.
> 
> So a question, Bjorn: do plants contain SiO2, or Si, which is incinerated and oxidized in the analytical lab? I can see the metal more than the oxide.



Ray, we have both a past in ceramic science so you are right, silica is SiO2. Si is absorbed by the plants though monosilicic acid Si(OH)4 which could be described as a (monomeric) hydrated silica. This monosilicic acid tends to polymerise, and then it cannot get adsorbed anymore. Polymerisation also takes place in the plant resulting in aggregates of polysilicic acid eventually aggregates of silica gel. These silica structures (amorphous) can be seen in the microscope. In phalaenopsis they appear as beads on a string like structures if I remember correctly. It is speculated that the silica-gel aggregates serves as catalysts (similar things are used in Chemical industry) for sythesis of stress related chemical compounds. At least some scientist believe that this could be the role. But these are new ideas and may not be easy to verify.
Amorphous silica can be glass but is actually any silica that has no crystallinity. E.g. silica gel, silica glass, fumed silica etc.


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## Bjorn (Sep 12, 2014)

AdamD said:


> So would DE contain silica in available form to the plant? Either foliage or roots?



That is one of the main silica fertilisers.


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## Bjorn (Sep 12, 2014)

AdamD said:


> So, I guess the follow-up would be, is potassium silicate the best available option? If pH were adjusted?



Higher pH gives more silica in solution. If you lower the pH, silica gel will be condensed. You might not see it it transparent and probably nano-sized.


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## Ray (Sep 12, 2014)

Thank you, Bjorn. I can wrap my mind around the acid, more than the oxide for absorption and transport!


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## troy (Sep 12, 2014)

My only question is could good humidity stiffen up leaves? Bcuse....


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## gonewild (Sep 12, 2014)

troy said:


> My only question is could good humidity stiffen up leaves? Bcuse....



Of course it can. leaves become more turgid (holding more water pressure) with humidity and water on roots. As leaves loose water pressure they become softer.


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## gonewild (Sep 12, 2014)

Bjorn said:


> Higher pH gives more silica in solution. If you lower the pH, silica gel will be condensed. You might not see it it transparent and probably nano-sized.



So in acidic conditions such as fertilizer solutions below pH6 used on orchids or orchid growing media that is normally below pH7 is silica soluble?


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## Bjorn (Sep 12, 2014)

gonewild said:


> So in acidic conditions such as fertilizer solutions below pH6 used on orchids or orchid growing media that is normally below pH7 is silica soluble?



It certainly is soluble, but only to some ppm. May be repeating myself, but soil often contains around 10-20ppm dissolved silica. Some may regard it as insoluble, but certain plants accumulate it to yield more than 50%of dry matter. Quite impressing taking into account what diluted solution it is (not orchids)


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## Bjorn (Sep 12, 2014)

troy said:


> My only question is could good humidity stiffen up leaves? Bcuse....



I have been adding silica to my water for almost a year now. Not the pro-tekt type though initially I thought that I saw stiffening, now I am not so certain anymore. Was it wishful thinking or some intermittent situation?


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## gonewild (Sep 12, 2014)

Next question when applying dissolved silica, such as protek, that is in a basic solution does the silica solidify and precipitate out?

I'm not doubting that plants use and need silica, I'm just suspicious of the benefit in applying it as a supplement in liquid form.
I have always thrown in various amounts of silica sand into my potting media thinking there must be a good reason for it.

I suspect that orchids get enough silica from the content of the media.
What is the silica content of bark, peat, perlite?


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## ALToronto (Sep 12, 2014)

Acids will definitely make dissolved silica precipitate out. It's an instantaneous effect. And if you ever allow a metal silicate to dry out and form a glass-like layer, acid will turn it into a much harder, no longer soluble glass. 

This is why Dyna-Gro recommends applying Pro-Tek separately from fertilizer, and it offers a different product to raise pH.


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## gonewild (Sep 12, 2014)

ALToronto said:


> Acids will definitely make dissolved silica precipitate out. It's an instantaneous effect. And if you ever allow a metal silicate to dry out and form a glass-like layer, acid will turn it into a much harder, no longer soluble glass.
> 
> This is why Dyna-Gro recommends applying Pro-Tek separately from fertilizer, and it offers a different product to raise pH.



Thanks.


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## Erythrone (Sep 12, 2014)

ALToronto said:


> Acids will definitely make dissolved silica precipitate out. It's an instantaneous effect. And if you ever allow a metal silicate to dry out and form a glass-like layer, acid will turn it into a much harder, no longer soluble glass.
> 
> This is why Dyna-Gro recommends applying Pro-Tek separately from fertilizer, and it offers a different product to raise pH.


Very interesting! Many thanks!


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## Ray (Sep 13, 2014)

ALToronto said:


> Acids will definitely make dissolved silica precipitate out. It's an instantaneous effect. And if you ever allow a metal silicate to dry out and form a glass-like layer, acid will turn it into a much harder, no longer soluble glass.
> 
> This is why Dyna-Gro recommends applying Pro-Tek separately from fertilizer, and it offers a different product to raise pH.



Whether it precipitates or not is also a matter of concentration. When I used to use it and Dyna-Gro "Grow" at equal amounts (approx a teaspoon per gallon) in RO, injecting the Pro-tekt into the solution containing the fertilizer (pH about 3.5) resulted in no precipitation.

As an aside, looking into silicon in Marschner's Mineral Nutrition book, silicon has been established as an essential nutrient in wetland grasses like rice, in sugar cane, and in tomato and cucumber, in the reproductive stage of growth only. No other plants seem to show signs of silicon deficiency.

However, there is some speculation that its deposition in the structural material may actually modulate the production of lignin. It takes 2g of glucose to produce 1g of lignin, and as the energy required to produce "pure" lignin is 20-times greater than that of the same structure containing silicon, that suggests that silicon can reduce the energy consumption related to plant growth. The question, of course, its to what degree.

Based upon my own experience, I see no need to add it, and folks jumping on the silicon bandwagon have been known to overdo it, with miserable results.


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## gonewild (Sep 13, 2014)

Ray said:


> Based upon my own experience, I see no need to add it, and folks jumping on the silicon bandwagon have been known to overdo it, with miserable results.



What type of "miserable result"? 
Bad result or just no result?


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## troy (Sep 13, 2014)

I've had a pint of pro-tek sitting on my shelf I'm taking it in to exchamge for fertilizer


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## troy (Sep 13, 2014)

Exchange


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## Jayfar (Sep 13, 2014)

ALToronto said:


> Certainly not PQ Corporation, the world's biggest producer of soluble silicates.


Funny you mention PQ. At this very moment, at the data center I work at, on the other side of the wall 20 feet behind me is a PQ Corporation warehouse.


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## troy (Sep 13, 2014)

PQ corporation?


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## Ray (Sep 15, 2014)

PQ = formerly Philadelphia Quartz Corporation, a major player in the silicon chemistry world.

Lance - "miserable results" meaning having no understanding that the very high pH will lead to rapid plant decline, and not putting two-and-two together.


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## troy (Sep 15, 2014)

Lol.. yeah I repotted a few plants and found silicone balls so I guess my good plant health is a result of good humidity lots of co2 and constant attention. Do you know what causes flower deformation?


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## gonewild (Sep 15, 2014)

Ray said:


> Lance - "miserable results" meaning having no understanding that the very high pH will lead to rapid plant decline, and not putting two-and-two together.



Thanks Ray.
That's an important comment.
Even though Silica is common and we tend to think about it as being inert it is not that simple when applied as a plant nutrient.
The method and materials used to get silica into a form that can be "sold" as a retail product seem to be a problem causer and potential for Growers to experience "miserable results". 

Because it is basically impossible to see positive results from adding silica I don't think it is a good idea to use it...unless you know what you are doing..... and are willing to accept the possible miserable result.


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## naoki (Sep 19, 2014)

I happened to see these papers related to the topic (I think they are accessible by anyone):

http://horttech.ashspublications.org/content/20/3/603.full
http://ufdc.ufl.edu/UFE0043381/00001


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## Brabantia (Sep 19, 2014)

Time to start a horsetail tea!


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## cnycharles (Sep 19, 2014)

i see lots of horsetails in my upstate travels (and nettles)


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## ALToronto (Sep 19, 2014)

Hemp is a good source as well. I add chopped hemp stems to the media of my potted orchids.


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## troy (Sep 20, 2014)

Thank you naoki


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## DavidCampen (Jan 16, 2015)

ALToronto said:


> I use soluble silicates in the production of my mineral composites. ... The alkali component is the carrier for the silicate component.
> 
> These are generally referred to as metal silicates and are written as M2O:SiO2, where M is the metal (Na, K or Li). The most important property of metal silicates is the molar ratio of the M2O component to the SiO2 component, i.e. how many molecules of M2O there are for every molecule of SiO2. ...
> Most industrial grade metal silicates have molar ratios between 2.0-3.5. These correspond to pH levels of 11-12. ...
> ...


 (Emphasis added is mine)

From what I find on the internet I am having a hard time deciding the exact composition of Pro-Tekt. I found an MSDS that lists it as *24.9% silicic acid potassium salt, specific gravity 1.2*. A Product Data Sheet states *potassium 3.7%, silicon 7.8% *. The Greenhouse Megastore description states *K2O 3.7%, SiO2 7.8%*. The label states *K2O 3.0%, silicon 7.8%*

The only way I see to make these numbers somewhat correlate is to assume 3.7% K20 and 7.8% Si (elemental) for the analysis while the solids (24.9% silicic acid potassium salt as stated in the MSDS) is calculated as the mass of K2SiO3 and H2SiO3 (or H4SiO4).

In any event, I have decided to start applying silicic acid perhaps once a week using Pro-Tekt as the silica source. I use 25 ml of Pro-Tekt and 8 grams of KH2PO4 each dissolved separately in about 750 ml of RO water and then the KH2PO4 solution is added to the Pro-tekt solution with rapid stirring. This gives a solution with a pH of about 7.2. This solution is then quickly diluted to 10 gallons with RO water to make the ready to use solution that I water with.


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## Bjorn (Jan 16, 2015)

David, if you add some diatomeous earth to your water, you will add silicid acid without changing pH. Eiter as a top dress or in the water. I add approximately 10ppm to my water intake and it dissolves before watering. I do not use DE though. My source is microsilica, or silica fume, but that is not so readily available as DE. But with similar properties as silica source.


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## DavidCampen (Jan 16, 2015)

Fumed silica is easy to get here. I thought of using that but I already had a bottle of Pro-Tekt.

http://www.multitechproducts.com/cab-o-sil-fumed-silica-aer-o-sil/?gclid=CLmJgd-GmcMCFcqVfgodjXkAbQ


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## Bjorn (Jan 16, 2015)

DavidCampen said:


> Fumed silica is easy to get here. I thought of using that but I already had a bottle of Pro-Tekt.
> 
> http://www.multitechproducts.com/cab-o-sil-fumed-silica-aer-o-sil/?gclid=CLmJgd-GmcMCFcqVfgodjXkAbQ



Common mix-up, silica fume and fumed silica.oke:
I do it all the time myself, but google microsilica, its slightly different. But guess a hydrophilic fumed silica could do the trick as well


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## DavidCampen (Jan 16, 2015)

Bjorn said:


> Common mix-up, silica fume and fumed silica.oke:
> I do it all the time myself, but google microsilica, its slightly different. But guess a hydrophilic fumed silica could do the trick as well



All the fumed silica that I have seen is hydrophilic. It will also have a smaller particle size and greater surface area than silica fume.
http://en.wikipedia.org/wiki/Silica_fume
http://en.wikipedia.org/wiki/Fumed_silica


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## Bjorn (Jan 16, 2015)

You can get hydrophobic as well. It floats on water and is impossible to mix in. Surface is grafted with silane, while normal silica has hydroxyl groups.


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## ALToronto (Jan 17, 2015)

David, the % of content listed on the Pro-Tek label is by weight. The molar mass of K2O is about 95, while for SiO2 it is 65. So those percentages must be divided by the respective molar masses to get the molar ratio.

The actual number is academic- I just wanted to point out that liquid silicates are not created equal.

For plants, I would be inclined to use organic sources of silica. I work with mineral silicates every day, and they don't really dissolve in pH-neutral water.


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## Bjorn (Jan 17, 2015)

AlToronto, just use microsilica, its the next big in silicon fertilisation. Actually today field test have been done with it with great sucess. As microsilica, or silica fume as its commonly called is amorphous, it solubility is much better than mineral (quartz) sources. But still low that is true. If you want silica to be soluble at higher levels, then you must push pH above 9 and that causes problems.


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## DavidCampen (Jan 17, 2015)

ALToronto said:


> ...
> For plants, I would be inclined to use organic sources of silica. I work with mineral silicates every day, and they don't really dissolve in pH-neutral water.


I made a silica solution today using the procedure I mentioned above except this time I used a little over 9 grams of KH2PO4 and the resultant pH was below neutral, about 6.8. This 2 liters of solution was clear with no evidence of turbidity. From what I have read, the solubility of silica in pH neutral water at room temperature is around 100 - 200 ppm.


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