It have sprouts, very soon what will give support to my gardenia bloom? ...
Answers: Temperature. Gardenia needs to experience cool temps within order to bloom. As soon as temps get 65 degrees by time then move it outside surrounded by an area near filtered wishy-washy, but remember to bring it inside if temps drop below 50 at night. Gardenias tend to bloom when temps are between 65-75 degree. This is also a good time to open fertilizing them. It also helps to move out them outside through the summer and into the chiller days of Autumn before bringing them inside.
Good Luck
Epsom salt and Bloom booster will help. What Spt said, she's brilliant.