For many years, gardenia bushes could only be successfully grown in landscapes in U.S. Department of Agriculture hardiness zones 9 and 10, but new hybrid gardenias are now available that are hardy to USDA zone 7b. With attractive, glossy, dark green foliage and intoxicating aromatic flowers, gardenia bushes are often planted near windows, entries and patios to take advantage of the appealing fragrance.
Native to Japan, evergreen azaleas are an ideal companion to gardenia bushes in your landscape. Both plants grow well in a more acidic soil with a pH value of 3.7 to 6.5, bloom in the spring and early summer and thrive in moist soil and partial shade. The vivid clusters of azalea flowers in shades of pink, red, yellow or white make a striking contrast to the delicate white or cream-colored flowers of the gardenia.
Like evergreen azaleas and gardenia bushes, camellia shrubs thrive in similar growing environments. Camellia foliage resembles the gardenia foliage with glossy dark green leaves, but the flowers of the camellia are much showier. Depending on the camellia variety you plant, the bush can bloom in fall, winter or spring and be covered with large bright blossoms in colors ranging from light pink to deep red that will continue to bloom for several weeks.
Masterwort, also known as astrantia, is a shade-loving perennial that grows to 1 to 2 feet high with striking and unique flowers in white, shades of pink and dark red, and it has foliage that offers a textural contrast to the gardenia shrub. Masterwort plants will thrive in soil of any pH, as long as it is in partial shade and moist soil. The flowering time of masterwort is long lasting from summer into fall.
Sweet marjoram plants are often used as companion plants to gardenia bushes to confuse and dissuade harmful insects and bugs. Sweet marjoram has an intense aroma, as do the gardenia blossoms, though of a different scent. It is used as a companion plant to gardenias as a pest repellent to mask the scent of the gardenia flower, thus repelling harmful pests like aphids, flower thrips and scale insects that are attracted to the flower's fragrance.