Homeowners and landscapers prize gardenias for their lush scent and double blooms. Most gardenias grown in gardens are shrubs, growing as tall as 6 feet. They are adaptable plants that grow best in well-drained acidic soil, pH 5 to 6.
Most garden-grown gardenias are cultivars of Gardenia augusta. They have a bush-like habit that varies in height from 1 to 6 feet. You can grow the smaller ones in containers. 'Radicans' spreads to 4 feet wide and reaches 1 1/2 to 3 feet tall. You can grown this cultivar as a ground cover.
Gardenia thunbergia, from South Africa, grows as an upright shrub or as a small tree. It can reach heights of 12 feet and a width of 7 feet. Unlike many gardenia varieties that bloom year-round, Gardenia thunbergia blooms only in spring or summer. It is a heat-loving plant that thrives in U.S. Department of Agriculture Plant Hardiness zones 10a to 11.
Although most gardenias do not need to be pruned, you can prune them to maintain their shape and height. Prune them after they flower so you do not reduce the number of blooms.