The gardenia's intense fragrance is an olfactory show-stopper. The shrub itself is pleasing, but when the soft white blooms appear in spring, it reigns supreme in the landscape. Nurseries also sell gardenias (Gardenia jasminoides) as a fussy houseplant, but homeowners readily forgive the plant's prima donna status once the flowers appear.
A chance encounter introduced gardenias to the New World. Tineke Wilders, writing in the North County Times, describes the merchant sailor Captain Hutcheson taking a stroll on a South African beach in 1794. A fragrance intrigued him, and he followed it to its source--creamy, double blossoms on an attractive shrub. Digging up a section, Captain Hutcheson returned it to England on his ship. John Ellis, a botanist in London, named this specimen after the American botanist Dr. Alexander Garden. The imported gardenia was propagated through cuttings and was cultivated as a houseplant.
Gardenia shrubs have emerald leaves and white blossoms. The leaves are leathery and evergreen, growing to a pointed oval. Gardenia varieties bloom from spring until late summer or fall, scenting the air with a spicy vanilla aroma from single or double flowers. The well-known variety "Mystery" has 4-inch double flowers and can grow 6 to 8 feet tall. "Veitchii" has 1-inch double blossoms on a compact, 3-foot mound. Grow gardenias as houseplants or in USDA zones 7 through 9.
Clemson University Extension suggests planting the ornamental, fragrant gardenia near walkways, patios or windows in the fall or in the spring. Plant in well-drained, acidic soils that remain evenly moist. Fertilize gardenias with an acid fertilizer, recommends the extension, in spring and in early summer. Do not fertilize in late summer or fall.
Gardenias are temperamental houseplants and demand attention. Plant gardenias in acidic potting soil, setting the crown above the soil level. Keep the soil moist without overwatering. Provide bright light, but do not allow the gardenia to sit in a hot window, and keep the air slightly humid. Fertilize monthly with an acidic, water-soluble fertilizer and leach the plant periodically to wash out excess salts.
The most common disease, according to the University of Rhode Island Horticulture Department, is canker. Canker is caused by a soil fungus, phomopsis gardeniae, that can be transmitted to other plants via pruning shears or other tools. The infected gardenia's stem is enlarged at the base and the diseased tissue becomes corky. Vertical cracks appear in the rough surface, and the stem above the affected area turns yellow. Destroy the plant and sterilize any containers or tools.
Two varieties of leaf spot affect gardenia plants. Bacterial leaf spot starts on new, young leaves, and rhizoctonia leaf spot affects mature leaves. Both are infectious. Overwatering and poor air circulation encourage rhizoctonia leaf spot, and diseased plants should be destroyed. Fungal leaf spots, which appear randomly on leaves throughout the growing season, are controlled with antifungal sprays.
Bud drop is not a disease. Bud drop frustrates gardenia owners, but otherwise promising buds fail in the normal course of a gardenia's bloom cycle. High night temperatures, low light conditions and uneven watering all exacerbate bud drop.