Bone meal help!

I'm creating a special flower

This flower will not generate in the normal world, the only way to get it is through bone meal, I would like to make it very rare, with the chance of being born at 1% or to grow a special flower for every 25 normal flowers or a special flower is born for every 15 bone meal used, how could I do that?

if there is another way to make this special flower rare, I would like to know, thanks!