Certified GKH Gardening Expert
Here are some articles that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-care-to-get-a-gardenia-bush-to-bloom.htm
You can grow them either in a pot or the ground, but in most climates they'll freeze out in the winter in a pot, should be fine in the ground. Try using a high phosphate fertilizer for blooming. Phosphate is the middle number. Example: A 9-59-14 is '59' phosphate. Anything that produces a flower or a fruit consumes more phosphates. Also, don't overwater. Too much water can reduce your blooms. You want the soil moist but not wet.