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A hardy gardenia, or Gardenia jasminoides, is a sub-species of the gardenia shrub more adapted to cold temperatures than its counterparts. All gardenias share basic characteristics like their shrub growth habit and fragrant flowers, but their ability to tolerate low temperatures differs among varieties. While most gardenias can tolerate temperatures down to 20° Fahrenheit (7° Celsius), cold hardy varieties can withstand down to 0° Fahrenheit (-18° Celsius). The hardy gardenia includes several varieties, including Kleim's Hardy, Chuck Hayes, and Frost Proof.
The gardenia is a flowering shrub native to China, Japan, and Taiwan. All varieties have a shrub growth habit and dark green, leathery leaves. Flowers range in color from white to yellow and typically produce a signature, very sweet fragrance. Shrubs flower from mid- to late spring and need plenty of sun and warmth during summer months to establish roots and survive the winter.
A plant's hardiness refers to its ability to tolerate a designated climate. Some countries have established hardiness zones that indicate specific temperature averages, and plants are labeled as hardy for designated areas. Gardenias, for instance, are usually only hardy down to zone 8, or 20° Fahrenheit (about 7° Celsius). A hardy gardenia can withstand colder climates, and there are several notable varieties of this kind.
Kleim's Hardy is an evergreen shrub with dark, glossy foliage and a slow growth habit. It grows to about 3 feet tall (appx. 0.91 meters) and about as wide. Its blossoms have six single petals with small yellow stamens. The shrub grows in a mound shape and is hardy down to about 0° Fahrenheit (-18° Celsius), though damage to foliage may occur.
Chuck Hayes is a second variety of hardy gardenia. This shrub produces fragrant blossoms with thick double petals resembling a rosette. Its foliage is also glossy and dark green in hue. Slightly larger than the Kleim's Hardy, it grows to about 4 feet tall (appx. 1.22 meters) and wide. The shrub is hardy down to zone 7 at 0° Fahrenheit (-18° Celsius).
Frost Proof, like Chuck Hayes, is a hardy gardenia with double blossoms, but its petals are slim. The flowers produce a sweet fragrance, and its long, narrow leaves are dark green and glossy. The shrub grows in a pear or vase habit, reaching 3 to 4 feet (appx. 0.91 to 1.22 meters) in height. This variety is also hardy down to zone 7.