Q.Gardenia Blooms
What causes our newly planted gardenias to develop browning of their blooms shortly after blooming?

It could be your watering practices. When watering, keep the leaves and flowers dry by applying the water directly to the mulch that surrounds the plant. Drip irrigation and soaker hoses are excellent choices for watering gardenias. Water droplets that remain on the plant can also make gardenia flowers turn brown or develop spots.
For additional information on gardenia problems, please visit the following link:
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/brown-spots-gardenia-buds.htm
Happy gardening!