Old fashioned gardenias or cape jasmines (Gardenia jasminoides) are reliably hardy in USDA zones 7-b and 8. Plants require immediate protection when the outdoor temperatures dip below 15 to 20 degrees.
The new hardier cultivars are compact growers, 2-4 feet tall and 3-4 feet wide. ‘Frost Proof’, Crown Jewel™, and Heaven Scent™ are three promising hardy cultivars to try in USDA zone 7-a. All three strut great thick, high gloss, dark green foliage.
Choose a garden location with good air circulation. Morning sunlight and afternoon shade is the rule. Plant gardenias in a well-drained acidic soil, and generously amended with compost. Water plants when dry and never overwater them. Acute leaf drop occurs in poorly drained soil. Fertilize once a year after the heaviest blooming cycle in June has past.
Fully capture gardenia's fragrance by planting in a garden spot or a container nearby a deck or patio. Individual blossoms generally last a few days. Flower loss may be rapid following a wind and rain storm.
Prune gardenias is immediately after blooming in early July. Remove all dead or unsightly shoots anytime you see them. Additional scattered blooms may occur anytime during the growing season. Late pruning should be avoided in the fall as next year's flower buds are being set.
White flies and flower thrips are major nemesis of gardenias. Bayer Advanced Tree and Shrub™ (soil drench) and horticultural oil (spray) should clean up most pest problems. Always read the pesticide label before using!