It??s harder to isolate a plant outside. Wind can carry pollen for miles. It??s a bit like saying, ??I have a hand full of fine dust, where can I stand so that if I release tiny bits of it all day long it won??t find my other plants.? You could also get it on your hands while your tending to it and transfer it that way. You could try things like placing it down wind of your other plants (winds change direction) or possibly at a higher elevation. Still though?think dust in the wind.

Good luck