The sub-zero hibiscus, as it is commonly sold, is actually a perennial plant called a rose mallow or swamp mallow that grows native to the wetlands of the southeastern United States. This perennial plant will grow up to 6 feet or more in a single season and produce large, tropical-looking flowers up to 12 inches across in zones where no tropical plants can grow. Use it in a low-lying area on your property, as it thrives under wet conditions.
Difficulty: Moderately Easy
Plant your hibiscus or rose mallow plant in a spot where it will get at least 4 hours of sunlight per day in rich slightly acidic soil filled with organic matter with a pH between 6.1 and 6.5. Keep it 3 to 4 feet away from other plants so it has room to grow. Dig the hole as big as the root ball using a regular garden shovel.
Water the perennial hibiscus with an inch of water per week if there is not enough rainfall, making sure that the soil stays moist and never dries out, as it is a wetlands plant. Reduce the watering amounts in the fall as the plant enters dormancy and then discontinue during the winter.
Mulch around the base of the plant with 4 to 6 inches of ground root mulch to keep the weeds under control as well as to conserve moisture around the roots.
Cut back the canes or stems of the hibiscus plant in the late fall after freezing temperatures have killed off the upper portion of the plant. Trim them down to as close to the ground as possible and then smooth the mulch over the crown of the plant.
No fertilizer is needed as long as the soil has plenty of organic material.