Tropical hibiscus plants are available at garden centers every spring. When summer is over, this tropical variety, Hibiscus rosa-sinensis, ends up in the trash or compost pile; they’re just not hardy enough to survive winter north of the tropics. And not many people have the right conditions in their homes to overwinter the plants indoors, either.
Did you know there’s a hardy hibiscus? Its Latin name is Hibiscus moscheutos and it is commonly called “mallow.” They are, of course related to the tropical hibiscus but are native to North America. They have the largest flowers of all hibiscus—some are twelve inches across.
Hibiscus moscheutos are reliably hardy to USDA Zone 4, and with extra winter protection, Zone 3. Although they have woody stems, they are considered perennials since they die down to the ground completely in winter.
Hardy hibiscus are one of the last plants to start growing in spring. Often it will be late May or early June before the stems start growing; don’t give up on them too early. They’ll bloom in July and will keep blooming until frost.
Pinch off the growing tips when the branches are about a foot tall. This will encourage the plant to branch out and produce even more flowers. It’s not unusual for a hardy mallow hibiscus to produce over a hundred blooms a season.
Plant hardy hibiscus in full sun in soil that holds a lot of moisture. This is one plant that will grow well in heavy, moist soil. Keep well watered throughout the growing season and your hardy hibiscus will continue to produce flowers even in the hottest part of summer.
When the plant is killed by frost, cut the branches off a few inches above the ground and mulch well before consistent freezing weather arrives.
Hibiscus moscheutos will even grow in bog- or swamp-like conditions. They are excellent candidates for low lying areas with poor drainage or for wetland gardens.
Hardy hibiscus grow rapidly to a height of about two feet. They make excellent summer hedges, quickly growing to define an outdoor “room” or special garden.
And they’re perennials, so you don’t have to plant them every year.