lt is not necessary to continue spraying a gardenia after flowering.
The reason for spraying is to stop the flower buds falling, which is quite possible, particularly, if the plant is growing in dry air.
Keep your plant warm, around 13°-16°C (55°-60°F), and water it when the compost is drying out.
Feed weekly, with a high-potash fertiliser from March to September, reducing to monthly at other times of the year.