I've never heard of using bicarbonate of soda on plants for any reason.

sure you don`t mean epsom salt ?

it is said that it helps prevent blackspot and powdery mildew once mixed and sprayed around, but i have not used it so cannot verify this.

I know it works on powdery mildew when mixed with water and dish soap. I don't know about black spot, since we rarely get that in the desert.

Thanx all. Reason I asked was, I'm trying to grow what looks like gherkins or at least that's what they looked like on the packet. But they're not looking too good. My daughter had a look at them today and said try using bicarb, because she too had heard about it and thought it was good for cucumbers. So basically, we've both heard about bicarb, but neither of us knew what it's used for or how to use it. ha ha.

I'd keep it for fruitcake.

I don't know about bicarb, but there is an excellent site on ways to use Hydrogen Peroxide in the garden at www.using-hydrogen-peroxide.com