Gardenias bring to mind Southern gardens, old-fashioned corsages and wedding flowers. Hardy from U.S. Department of Agriculture plant hardiness zone 8 to 10, gardenias are not native to the New World. Gardenias can live for decades in the right spot, but cultural factors can limit their ability to adapt to many North American climates, giving them a reputation as, at best, finicky and, at worst, short-lived.
The gardenia traveled from its native East Asia around the Cape of Good Hope to Europe, garnering it the nickname Cape jasmine on the way. It found a home in the 18th century colonial gardens of semi-tropical coastal South Carolina. Like other broadleaved evergreens, gardenias cannot tolerate cold temperatures, although some shrubs have the ability to re-sprout after dying back. Temperatures below 20 degrees Fahrenheit often kill the shrubs. Of course, planting a gardenia in a USDA zone below its hardiness -- zone 7b in the case of the hardiest plants -- makes for a lifespan of a few months rather than years.
Tropical in origin, gardenias tolerate semi-shade to full sun exposures but their glossy leaves demand constant moisture to stay healthy. Heavy, waterlogged soil strangles roots, limiting bloom and eventually weakening the plant, resulting in its death. Well-drained, highly organic soil irrigated regularly using the drip method, on the other hand, can contribute to a plant’s longevity. Plants in full sun bloom more heavily, but they also require more moisture and their thick leaves might be subject to sun scald. Gardeners in Mediterranean or other dry climates should locate their plants in partial shade with some morning sun to encourage good bloom and healthy foliage.
Soil and Nutrients
Acidic soil and plenty of composted mulch provide enough nitrogen to Southern gardenia, but soil in other areas may need help meeting the gardenia’s needs. Before planting the shrub, a soil test will reveal factors that can lead to short lives; alkaline pH, lack of iron or manganese, for example, can limit life to a few years. Fertilizer applied in late fall encourages a flush of tender new growth that might be killed back in cold weather, stressing the plant and leading to death. A gardenia fertilized in early spring and again after bloom, though, gets its extra nutrients as it begins growth and as it recovers from the effort of blooming -- just when it does the most good.
Potted gift gardenias are typically short-lived -- a year or less -- because indoor plants forced in greenhouses seldom receive the light and humidity to sustain them. Pots or containers might allow Northern gardeners or gardeners with moving sun and shade to keep nursery-raised gardenias healthy, however. The florists’ gardenia’s lifespan might expand a few years from spending warm weather outdoors -- and containerized shrubs, given enough light and moisture indoors, could live to bloom another spring.