Silicon is the second most abundant element in the crust of the Earth. Oxygen is first. Our soil is naturally rich in silicon, and a number of broadleaf plants and grasses are able to absorb it into their tissues. Unlike minerals like phosphorus and nitrogen, silicon is not essential for plants to survive. However, for reasons that scientists are trying to determine, it has been observed to provide various benefits for some flora.
Silicon is said to be especially positive when plants face stress. Through absorption, plants improve their ability to withstand droughts and are able to survive longer stretches of time without water before wilting.
Moreover, in rice and wheat, silicon can improve the strength of the stem. Without it, they become weakened and may be damaged by the weather. In some cases, it has been found to make plants more resilient to attacks from fungal pathogens, too.
That said, silicon is only beneficial in moderation. Excess levels have been shown to impair and damage flowers in sunflowers and some species of daisy.