Gardenias, popular shrubs grown for their fragrant flowers, perform best when provided with warm temperatures and humid air. Gardenias produce showy, aromatic blooms with proper care, though the strength and sweetness of the scent may be over-powering to some. For the best results, place the shrubs near walkways or porches, so their fragrance can be fully appreciated without overwhelming the senses. Hardy in USDA zones 8 through 10, gardenia shrubs cultivated outside these areas require planting in containers to bring indoors over the winter months. In some cases, gardenias may survive winter in zone 7, though they usually die back to the ground when temperatures drop below freezing.
Plant gardenias during spring or fall in a location that receives partial shade throughout the day and consists of acidic, well-drained, moist soil. Apply a 2-inch layer of ground bark to the planting site and use a garden tiller to amend the soil, increasing drainage and fertility.
Spread a 2- to 3-inch layer of mulch over the ground surrounding gardenias to improve moisture retention, insulate the roots and stunt the growth of competitive weeds. Allow at least 3 inches between the plant's crown and the mulch layer to provide air circulation.
Water gardenias once per week during the spring and summer months to keep the soil moist at all times. Soak the soil to a depth of 6 inches at each watering. Decrease the frequency of watering to once every 10 days during fall and winter, when active growth has ceased.
Feed the shrubs twice per year, once in early spring and again in mid-summer, using an acidic plant fertilizer. Water lightly before and after feeding to prevent root burn or injury. Read the manufacturer's instructions for proper application and dosage.
Prune gardenia shrubs immediately after flowering ends to keep the plant compact, healthy and attractive. Use hedge clippers to remove any diseased or damaged limbs and spent flowers, and to cut back any excessively long growth.