Im planning on making my own colloidal silver and was wondering what is the optimal PPM for use on plants?

1000ppm to 2500ppm is what i have read is necesary to cause male flowers to form.

Do you apply the solution to the root zone or is it foliar fed?

its hard to say ppm when making your own the best way is to just do a couple hours burst of electricity like 3

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too high a ppm is better than too low its pretty non toxic anyways. as for spraying spray the foliage that you want to produce male flowers on. you could do one branch or the whole plant spray at 3 day intervals some people cover the treated branch with clear plastic to effect ethylene concentrations and possibly speed the process.

Colloidal silver may be generally non-toxic to plants, but ionic silver like you need is a different story.. Silver ions disrupt ethylene (a hormone) activity..
From what I've read, typical applications seem to be about 500-1000ppm, but lab writeups are likely to use actual molar concentrations whereas our tds meters are calibrated against NaCl's electrical conductivity in solution, so I'm thinking bicycle racer's numbers might be an ok target..
You want to foliar feed it, and you should add a touch of soap or other surfactant so the spray doesn't just bead up..