While your "Hardy Daisy" gardenia (Gardenia jasminoides or augustus "Hardy Daisy") is a dwarf cultivar that won't grow to block a window or tower over the surrounding landscape the way some flowering shrubs can, that doesn't mean you get out of pruning duties. "Hardy Daisy" tops out at 3 feet tall and is one of the more cold tolerant of this warm-weather-loving species, thriving in U.S. Department of Agriculture plant hardiness zones 7 through 10 -- a full zone cooler than the typical gardenia. To keep the plant covered in 2-inch, single blooms that are white with yellow centers like its namesake, prune after flowers fade in late spring.
Clean the blades of your bypass pruners or loppers with household antiseptic cleaner. Dry them with paper towels. The cleaning fluid helps eliminate any remnant of plant disease or fungus that might remain on the blades from the last time you pruned.
Thin any congested, dead or broken branches at the base of the stem once all threat of frost has passed to clean up the plant, and to let in more light and air to prevent legginess -- the term for when the bottom of the stems drop their leaves. "Hardy Daisy" doesn't suffer cold damage -- dead leaves and blackened stems -- above zero degrees Fahrenheit, but you can simply remove any cold-damaged stems at their base.
Pinch off flower heads at the base as they fade to tidy up the appearance of your gardenia and to channel the plant's energy toward new growth. Your fingers should do the trick, but bypass pruners may be faster.
Shorten, or head back, stems to three-quarters of your desired height for a mature "Hardy Daisy" gardenia plant if it didn't bloom much this year. Cut at a 45-degree angle with bypass pruners to 1/4 inch above a side branch or leaf bud, so you don't leave a stub that will die off. On young plants, cut back to above the first or second lateral shoot from the tip of the plant.
Pinch out the growing tips of new growth rising from your heading cuts when it is a few inches tall. This promotes more branching and flowering points for next spring's flowers. You can pinch younger plants that are growing vigorously at least one more time if you want an even bushier gardenia. Don't pinch past late summer to allow new growth time to harden off and set buds before temperatures cool.