This article is republished from Garden Culture Magazine, Issue 7 where it appeared under the same title.

“The biochemistry of Silicon in plants is a riddle, wrapped in a mystery inside an enigma.” — (Epstein, 2001)

Silicon is still not as well understood today as many of the other elements that we commonly use in our plant feeding regimes. It’s probably not used as widely as other additives, and yet it is (in my opinion) one of the most important tools in a grower’s arsenal. I say this because of what it can do for your plants throughout all stages of growth and reproduction. The benefits vary from helping the plant to support itself through stronger cell walls to preventing pests from making their homes on your petunias, stopping disease in its tracks, and allowing plants to survive in very hot/cold conditions. If you don’t currently use a Silicon product, get it on your shopping list for the next time you’re at the grow shop and enjoy the sense of calm that this product will afford you.

Here’s the science

Plant roots take up Silicon, chemical symbol ‘Si’, in the form of silicic acid (Si(OH)4), it is then transported from the roots to the shoots via the xylem and distributed around the plant organs depending on transpiration rates of each plant organ. The epidermal cell walls are impregnated with a layer of Si, and become effective barriers against water loss by cuticle transpiration and fungal infections.

There are two hypotheses for how Silicon protects a plant. The first one says that the Si acts as a physical barrier, the Si is deposited beneath the cuticle to form a Cuticle-Si double layer and protects the plant mechanically by withstanding pest and disease penetration into the leaf. The other method says that plants supplied with Si produce phenolics, lignin, H2O2, and phytoalexins in response to fungal infection.

Silicon alleviates various abiotic stresses, including physical stress (drought, radiation, high and low temperatures, and freezing), and chemical stress (salt, metal toxicity, and nutrient imbalance). Si relieves water stress by decreasing transpiration, as this mainly occurs through the stomata, and partly through the cuticle, Si deposited below the cuticle may decrease any losses.

Lastly, Silicon is not a mobile element, so any deficiencies will show up on younger leaves. It is not classed as an essential nutrient as a plant can grow and reproduce without it, but for many gardeners, including myself, it is a crucial part of my feeding regime.

Silicon in the grow room

I know some of you reading this may think, “I’ve never used Silicon before and I’m doing great”, but that’s just like saying “I built a house from just bricks and mud and it looks good to me”. Well, if you added cement to those bricks, you could have a bigger house and one that’s going to stay up a lot longer. Silicon is the cement in that metaphor and including it will give your plant extra support, improved growth, and bigger yields.

There are a lot of silicon products on the market, and some companies say that their Silicon product does not affect pH as dramatically as others, this is a marketing trick and although it’s true what they say, it’s because they have likely watered down the silica so its effect on pH is not as drastic. Don’t be fooled by creative marketing.

Lastly, the method of adding the silica to the nutrient tank is very important. Here’s what you should be doing to prevent the solution from becoming cloudy, which means the silica has precipitated out of the solution, and become less available to the plant. Firstly, add the silica to your water tank and measure pH, next step is to reduce the pH to 7 and add the rest of your nutrients, lastly adjust pH to desired range depending on the type of plant being grown, this is typically between 5.8 and 6.3. This method, although time-consuming is best practice for getting the most out of your plants whilst using silica.

I hope this first article in the ‘What is…’ series has been beneficial to you, and that you feel that Silica is an additive worthy of your feeding regime. I can tell you, with good authority, that it definitely isn’t a Silly-Con…