Typical gardenia (Gardenia jasminoides) includes cultivars ranging in size from 2 feet tall up to 15 feet tall. These plants have glossy evergreen leaves, but are possibly best known for their big, fragrant white flowers. Gardenias grow in U.S. Department of Agriculture plant hardiness zones 8 through 11. The plants prefer full sunlight to partial shade and acidic soil with a pH selection of 5.0 to 6.0. Choose companion plants with similar needs to make maintenance easier.
Shrubs
Bigleaf hydrangeas (Hydrangea macrophylla), which grow in USDA zones 5 through 9, withstand exceptionally acid to alkaline soil, however, the soil pH affects the flower color. When grown along with gardenias, your bigleaf hydrangeas will create bright blue flowers, especially when the soil pH is closer to 5.0 or closer to purple with a pH of 6.0. Indica azalea hybrids (Rhododendron indicum), best for USDA zones 4 through 9, create papery pink to red blossoms that pop against gardenias. Azaleas do best with a soil pH between 4.5 and 5.5 and, while they grow in sunlight, they do best using partial shade against the morning sunlight, especially in winter.
Perennials
The rose genus (Rosa spp.) Includes about 150 species in a variety of colors that grow within USDA zones 2 through 10 and need loamy soil with a pH between 5.5 and 7.0. Forms include ground covers, upright shrubs, compact shrubs and climbing roses. Astilbe (Astilbe spp.) Adds texture to balance the delicate features of gardenias, but must be utilized if gardenias are planted in full colour. These spiky plants, which thrive in USDA zones 4 through 8, need moist soil with a pH between 5.5 and 6.8. Add pops of color with whimsical foxglove (Digitalis spp.) , which includes tall spikes covered with many bell-shaped flowers. Foxglove typically grows best when given partial shade, but Mediterranean foxglove species bear sunlight. They climb in USDA zones 3 through 9 and prefer soil with a pH level of 5.5 to 6.5.
Annuals
China asters (Callistephus chinensis) bloom in hues of blue, red, pink and white and would make suitable edge annuals about gardenias. China asters thrive in sunlight and acidic soil, but also bear loam and alkaline soil. Marigolds (Tagetes spp.) Thrive in sunny spots with slightly acidic soil with a pH between 5.8 and 6.5. These also make suitable border plants and keep garden pests away. If you want to grow a low, compact border around your gardenias, consider annual phlox (Phlox drummondii), that grows up to about 1 foot tall with glowing red, pink, purple or white blooms. Annual phlox prefers slightly acidic soil with a pH less than 6.8.
Trees
Southern magnolia (Magnolia grandiflora) is known for the pleasing scent of its big, creamy white flowers and like gardenias, feature glossy, oblong evergreen leaves. Magnolias thrive in full sunlight to partial shade in USDA zones 7 through 9 and need a soil pH level between 4.0 and 6.0. Many coniferous trees need soil pH between 5.0 and 6.0, such as loblolly pine (Pinus taeda), which grows in USDA zones 6 through 9. You will want to distance your gardenias from this dense shade tree, however American beech ( Fagus grandifolia) grows in USDA zones 3 through 9 and thrives in soil with a gardenia-friendly pH between 5.0 and 6.5.