Hibiscus are very attractive shrubs that sport large blooms, which attract butterflies and humming birds. The hardy hibiscus, also known as rose or swamp mallows, was developed by the Fleming Brothers and have a more compact growth habit than the tropical hibiscus species. Hardy hibiscus are used for borders or in large planters, surviving to -30 degrees F and thriving in USDA zones 4 through 9. Choosing companion plants for the hardy hibiscus is not difficult. In fact, there are many attractive plant species that make for good companions.
Plant the coreopsis, also known as "tickseed," after all danger of frost has passed, allowing a 1 foot radius for their growth. Coreopsis are bushy plants, reaching about 2 feet in height. You can plant them in sandy soils, and once established they will not require fertilizer and do not need much water. Coreopsis bloom all summer and into the fall with large flowers that will remind you of daisies. Dig up and separate coreopsis every two or three years.
Plant campanula persicifolia, or "blue waterfall," as a companion to the hardy hibiscus. Blue waterfall is a very easy and adaptable plant to grow, and is often used as ground cover. Plant blue waterfall in full sun after the last frost and feed it an application of a slow-release fertilizer once a year, also in the spring.
Plant the mango meodowbright coneflower (an echinacea hybrid) as a companion if you have poorer soil quality. This plant will adapt to a wide range of conditions, featuring large yellow blooms from summer until the first frost. Give this plant a slow-release fertilizer once every spring and it will grow to 2 feet wide and reach 2 to 4 feet in height. Be sure to plant it in full sun or partial shade and leave the seeds on the flower heads to attract song birds.
Try baptisia as a companion to the hardy hibiscus. Baptisia is a flowering perennial with blooms that resemble pea blossoms that grows to 4 feet high and 3 feet wide. The plant will bloom starting in June and throughout the whole summer. The plant has dense foliage and likes full sun and well-drained soil. When planting, space the baptisia plants 20 to 30 inches apart.
Try a mixture of other easy-to-grow companion plants, such as daylilies, delphinium, alium, poppies, peonies and bearded iris. They all grow well in the same soil condition, light and water requirements as the hardy hibiscus.