Hibiscus Grandiflorus Care: Learning To Grow Swamp Rose Mallow

Hibiscus Grandiflorus [hi-BIS-kus, gran-dih-FLOR-us] is a perennial herbaceous flowering shrub from the mallow or family Malvaceae. 

Endemic to the United States, the native plant mainly grows in wet and open areas, such as marshes, swamps, ditches, and alongside lakes, ponds, rivers and the rain garden.

Blooming Hibiscus Grandiflorus aka Swamp Rose Mallow
Image: Mackenzie from Washington, DC [CC BY-SA 2.0], via Wikimedia Commons

Hibiscus Grandiflorus is sometimes also known by another scientific names:

However, it is generally known with the following common names:

  • Swamp rose-mallow
  • Pink swamp hibiscus
  • Large-flowered hibiscus
  • Hardy hibiscus
  • Velvet mallow

Hibiscus Grandiflorus Care

Size & Growth

Swamp rose-mallow is a large deciduous shrub, typically growing up to 6’ feet in height and feature large showy blooms, heart-shaped leaves, and pubescent stems and bracts.

The leaves are three-lobed, alternately arranged and have a grayish-green color, which gives the foliage a light silvery tinge. 

They have toothed margins and a velvety texture.

Rose Mallow Flowering and Fragrance

The bloom time starts in late spring till late summer or early fall (March to August), this Hibiscus produces 4” to 6” inch long solitary blossoms. 

The bloom color of each flower has five light pink petals with red to purple center and multiple yellow stamens; the contrasting flower colors make a beautiful display.    

Light & Temperature

This mallow species grows best in full sun; the more sunlight it gets the more flowers it produces. 

However, they can tolerate partial shade.

It thrives in warm weather; warmer temperatures are particularly good for bud and flower growth.

It is hardy to hardiness USDA zones 8 to 11.

Watering and Feeding

Since Hibiscus moscheutos is a wetland plant and grows in swamps and marshy areas in its native habitat in North America, it needs regular and ample watering when grown in gardens or pots. 

The plant sheds its flower buds and also becomes susceptible to diseases and pests if its water requirements are not met. 

Like with many other perennials, the newly planted grandiflorus needs more frequent watering than the established plants.

Swamp rose-mallow is not drought tolerant.

When it comes to feeding, the hibiscus moscheutos responds well to organic fertilizers. 

However, it doesn’t need too much fertilizing – an application of compost once a year, ideally in spring, is enough. 

Alternatively, apply a 10-10-10 fertilizer around the base.

More of Tips on Fertilizing Hibiscus

Soil & Transplanting

As evident from its common names, swamp rose-mallow and pink swamp hibiscus, the plant likes wet soils. 

However, it usually easily adapts to standard gardening conditions and grows well in house gardens too.

From clay to sand and acidic to basic, the plant can tolerate a wide range of soil types, but it grows the best in well-draining soil containing a sufficient amount of organic matter.

Grooming and Maintenance

Large-flowered hibiscus needs little grooming and maintenance. 

In fact, the dead stems make a beautiful display in winters, when they get covered with frost and snow.

Cut the old stems back to the ground as the new shoots start emerging, in spring.

While some people prune the new stems in early summer because it is known to encourage a bushier shrub, it is not mandatory as the plant will do fine without it too.

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How To Propagate Swamp Rose Mallow

These wildflowers are propagated by seeds, stem cuttings, and divisions.

While it is easy to grow H. grandiflorus from seeds, the seedlings do not always resemble the parent.

Stem cuttings root more easily if taken before the beginning of the blooming period.  

Growing from seeds:

Collect the seeds when the seed pods turn brown and start to split and sow them in fall or store for later use.

If sowing before the end of the frost season, sow the seeds indoors for 12 weeks. 

If growing outdoors, wait for the last expected frost date and then sow the seeds in the ground.

Propagating through stem cuttings:

Take 5” to 6” inch long, pencil-thick cuttings from the new, firm growth. 

Remove the lower leaves and plant them in a potting mix prepared with one part peat and three parts sand. 

The cuttings will develop roots with four to five weeks.

While stem cuttings grow the quickest in spring, plant them at any time when new growth is available.

Propagating by plant division:

Divide the plant in spring, particularly when dealing with soft, new growth because they cannot tolerate fall divisions.

Swamp Rose Mallow Pest or Diseases

Rose mallow plant may get affected by whiteflies, aphids, and Japanese beetles and as mentioned above, the pest issues get worse if the plant is water-stressed. 

But, in most cases, pests can easily be controlled with the application of organic insect controls available in the market.

The plant may develop fungus if it is planted in an area with poor air circulation if the diseased leaves are left on the plant, or if the mulch is touching the stem.

The seed pods of the hibiscus plants attract birds, particularly in winters when there is very limited food available.

In winters, the seed pods serve as a food source for different types of birds. 

The pink flowers, on the other hand, attract hummingbirds and butterflies.

Moscheutos Hibiscus Uses

The plant is primarily grown for its large and strikingly beautiful flowers.

Due to its big size, pink swamp hibiscus is best suited for large landscapes and rain gardens. 

However, it also makes a stunning centerpiece in mixed pot gardening.

The leaves, flowers, shoots, and roots of young grandiflorus plants are used for culinary purposes in some parts of the world.