CHANGE TO PINK CHANGE TO PINK For hydrangea blooms to be pink, the plants must not take up aluminum from the soil. If the soil naturally contains aluminum, one must try to keep.... Choose a fertilizer close to the ratio of 25/10/10 (Phosphorus is the middle number). In areas that naturally produce blue hydrangeas (soils with aluminum), consider growing pink... hydrangeas in large pots. If hydrangeas are grown in pots, it would be best to use soil-less mixtures, since these mixes would probably not have aluminum in them. In a pot, it will be much easier to control the requirements for growing pink hydrangeas. ...