Hardy hibiscus, sometimes known as rose mallow, is a tropical flowering plant valued for its large colorful blossoms, ease of care and its hardiness in the garden. The plant is hardy to USDA Zone 4, which means it can be left outdoors during winter in most areas of the United States to re-emerge the following spring. Planting hardy hibiscus is easy if the proper growing conditions are met. With a little effort, you can grow these attractive perennials in borders, near patios or entryways, or even as mass plantings to add a tropical touch to your garden.
Plant hardy hibiscus in early spring or fall when the soil is slightly moist, but not wet. Choose a planting location that receives at least five hours of full sun per day and has moist, average, well-drained soil for the best results.
Amend the planting location prior to setting out hardy hibiscus. Spread a 2- to 3-inch layer of organic compost over the site, and then use a garden tiller to incorporate the matter into the soil to a depth of about 6 inches.
Dig planting holes for your hardy hibiscus plants about 4 to 5 feet apart and of equal depth to the container in which they were previously growing. Place each plant into a hole and gently back-fill with soil to cover the roots.
Water hardy hibiscus immediately after planting to compact the soil. Continue watering once per week, or often enough to keep the soil consistently moist at all times. Increase watering to twice per week when temperatures rise above 85 degrees F.
Apply a 2- to 3-inch layer of mulch to the soil surrounding your hardy hibiscus just after the initial watering. This will help the soil retain moisture, which is necessary for the health of the plant, and suppress weeds. Replenish as necessary through the year.
Feed hardy hibiscus plants just after flowering begins using a water-soluble fertilizer according to the manufacturer's instructions. Continue to feed the plants once per year in spring, just after they begin to bloom.