I honestly have no clue. I've planted it next to 2 flowers, watering them and got nothing. If someone could show with a picture I'd be really grateful :3 Btw, this is only for 2 flowers (if it matter's lol)
My first try with fertilizer got me a black rose. Second got me a red one. Fertilizer is still worth it, but I wouldn't be betting on it if fertilizer was involved.