Plagron - Silic Rock

A silicon fertiliser, registered as NPK 1.5-0-1.7 with 1.0% SiO2. A maximum of 1 ml per litre at every watering, throughout the cultivation. Note: the product's own pH is 1.5, and it is not suitable for recirculating hydroponics.

The pH is 1.5, and that is not carelessness

Plagron give this product a pH of 1.5. That is exceptionally low, lower than most pH-down products on this shelf, and it is the first thing to know about the bottle.

There is a reason behind it that has nothing to do with your water. Dissolved silicon tends to bind to itself: individual molecules react with one another into ever larger structures, a process called polymerisation. The further that goes, the more viscous the liquid becomes and the less of the silicon remains in the small, directly absorbable form.

A strongly acidic environment slows that process down. Plagron therefore formulate the product at pH 1.5, not to acidify your nutrient solution but to keep the silicon in the bottle available for as long as possible.

What that means for your reservoir

Two practical things follow, and neither appears on most web shops.

First: this product lowers the pH of your nutrient solution. At 1 ml per litre the effect is not dramatic, but it is there, and it depends on how much buffering your water has. So measure your pH after adding Silic Rock and only then correct with your pH product, not the other way round. Do it in reverse and you set it neatly, then push it back down yourself.

Second: if your bottle thickens over time, that is expected ageing and not spoilage. Plagron say explicitly that increased viscosity does not mean the product has stopped working; even in a partly polymerised solution a portion of the silicon stays available. What it does mean is that a bottle left standing for years delivers less than a fresh one, so buy a size you will get through in reasonable time.

Plagron also advise dissolving Silic Rock properly before adding other products. For this product that is a genuine manufacturer instruction, not a general rule of thumb.

It is also simply a fertiliser

The registration is NPK 1.5-0-1.7 with 1.0% silicon dioxide. That is the honest picture: alongside the silicon, this bottle also supplies a little nitrogen and potassium.

Plagron tie that potassium in themselves: they attribute the effect to the ratio of silicon and potassium together, not to the silicon alone. They further state that silicon mobilises less mobile components in the soil, improving uptake of phosphorus, calcium and micronutrients.

Not in a recirculating system

Plagron give this as unsuitable for hydroponics: no NFT, no deep water culture, no aeroponics. The reason they give is that the product is of organic origin.

You will find listings online marking it as hydro-suitable. We do not follow those; the manufacturer's own statement governs here. For soil and coco it is intended.

In use

Shake well before use. Mix a maximum of 1 ml per litre of water, a ratio of 1 in 1000, and feed it at every watering throughout the cultivation.

Available sizes

Technical Specifications:

• Type: silicon fertiliser, NPK 1.5-0-1.7
• Manufacturer: Plagron
• Silicon dioxide (SiO2): 1.0%
• Product pH: 1.5
• Dose: maximum 1 ml per litre of water (1 in 1000)
• Frequency: at every watering, throughout the cultivation
• Substrate: soil and coco
• Not suitable for: NFT, deep water culture and aeroponics
• Order: dissolve fully first, then add other products
• Before use: shake well

Frequently asked questions

Does this change the pH of my feed water?
Yes. The product's own pH is 1.5. So measure and correct your pH only after adding Silic Rock.

My bottle has thickened, has it gone off?
No. Dissolved silicon polymerises slowly, making the liquid more viscous. Plagron state that this does not render the product ineffective.

Why is the pH so low?
To slow that polymerisation and keep the silicon in absorbable form for as long as possible.

Can I use it in my hydro system?
No. Plagron give it as being of organic origin and therefore unsuitable for NFT, deep water culture or aeroponics.

When do I add it?
First, dissolving it fully before adding the rest of your feed. That is Plagron's own instruction.