Gardenias are extremely fragrant, tender perennials with delicate white flowers. They are only reliably hardy south of USDA Zone 6, or where winter temperatures don't get colder than 15 degrees. In colder northern areas, grow gardenias in pots and bring indoors over winter. Gardenias grow best in full sun but will do well in partial shade, especially in extremely hot locations.
Place the gardenia in full sun to partial shade. The soil should be on the acid side with a pH between 5 and 6. They like rich, friable soil that is well-drained.
Improve the soil before planting. Add 2 to 4 inches of peat moss to the surface of the soil. Turn the soil over with a shovel to incorporate the peat moss into it. Rake the soil smooth.
Plant the gardenia. Dig a hole that's twice as large as the plant's root ball. Add an equal amount of peat moss to the soil you removed from the planting hole and mix in well. Add 2 tablespoons of high-acid granulated fertilizer to the bottom of the planting hole. Scratch it into the ground with a garden claw. Add some improved soil to the bottom of the hole and set the root ball on top of it. Back fill the hole the rest of the way and firm the surface with your foot.
Make a ridge around the edge of the hole on the surface of the soil with your hands. This will direct water to the roots of the gardenia.
Place a hose, set to a slow trickle, near the base of the gardenia. Allow it to water the plant for 20 to 30 minutes. Water gardenia 1 to 2 inches of water per week.
Mulch around the plant with shredded pine bark, buckwheat hulls or pine needles. Organic mulch is best because it will add to the richness of the soil as it breaks down.
Cover the roots with 1 to 2 feet of fallen autumn leaves or hay in fall to protect the roots from cold winter temperatures. Remove the protective mulch in early spring when temperatures reliably stay above 20 degrees.
In spring, give the gardenia a fertilizer specially formulated for acid-loving plants. Pull the mulch back, scatter the granules around the base of the plant and scratch it into the soil. Replace mulch.