Hibiscus moscheutos, a huge-flowered shrub with stunning blooms

Hibiscus moscheutos is a powerfully ornamental marsh plant with large leaves, sublime flowers, and many sturdy upright stems.

H. moscheutos key facts:

Botanical name – Hibiscus moscheutos
Family – Malvaceae (mallow family)
Type – wet soil perennial

Height – 4 to 6 feet (1.20 to 2 m) or more
Exposure – well-lit
Soil – rich, moist

Foliage : deciduous
Flowering : end of summer

A perennial with deciduous leaves, swamp mallow or Hibiscus moscheutos is a pondside plant that’s perfect to decorate a body of water or a garden basin. In summer, the plant is wreathed in gigantic saucer-shaped flowers (6 inches across or more, 15 cm!).

They’re generally white with a blood-red center, but sometimes red or pinkish varieties can be found. Hybrids expand the range of colors, and flowers can even reach up to 9 inches across (22 cm).

Planting Hibiscus moscheutos

Swamp mallow should only really be planted outdoors, siding a body of water (slightly acidic water is best).

Hibiscus moscheutos is quite a large shrub, massive in fact, that is best as a standalone. The feature that most gardeners love about it is the astounding blooming (September). Nonetheless, they’ll also fit together with other shrubs in a shrub bed if the space permits, but each plant will need its own spot, they won’t grow very well if they’re crowded together:  at least 3 feet to all sides (1 meter).

• Exposure should be full sun.
• This species prospers in sunny, wet spots: pollinators love it, it calls out to them like a beacon.
• Best are wet, moist soils that are very rich (with lots of organic matter).
• Simply dig a hole large enough for the clump to fit right in after you tease it from the pot it was purchased in.

These plants also cope with clay, mud and shallow sitting water. Interestingly, they’re also pretty tolerant to drought once they’ve settled in well.

Use in landscaping

The showy flowers of Hibiscus moscheutos will draw the eyes in an aquatic garden setting. Such plants also grow well in containers, they’re placed to attract butterflies in parks, around vacation homes, in wet, marshy landscaping, low-maintenance gardens, as perennial edges and in humid areas.

Try pairing Hibiscus moscheutos with Asclepias incarnata, Eupatorium fistulosum, Helianthus angustifolius, Lobelia cardinalis and Panicum virgatum.

Again, make note of the size of this plant: it may quickly block the sun out from nearby flowers and crops.

Growing and caring for swamp hibiscus

Shrubby shoots (that don’t branch out) surge out from the roots; they die back in winter. In winter, it’s important to cover the plant (what’s left of it underground) with a thick layer of dead leaves, especially if it freezes in your area. This relatively hardy plant, when mulched, will survive freezing down to 23°F (-5°C), and even a bit colder if only for one night.

Stems are sturdy and only rarely need staking. Cut them back to ground level at the end of winter: this favors the emergence of new, fresh growth.

The hibiscus clusters start growing quite late in the season. Young plants, less than a year old, require regular, deep watering, without ever letting the soil get dry.

Propagating Hibiscus moscheutos:

Hibiscus moscheutos multiplies easily through seed sowing, clump division, and cuttings.

• Sowing: seed pods ripen and turn brown within 4 to 5 weeks after the blooming. The seeds are ready for harvest when they’re dark brown. If needed, cull out any seeds that are infested with weevils, and keep the healthy ones in a container in a cools spot: you can sow them in the middle of spring the following year. Sow in soil mix that you keep consistently moist, with lots of nutrients. Not soggy, just moist.
• Division: it’s possible to divide the clump, but it’s difficult because roots tend to dive deep into the soil.
• Cuttings: semi-hardwood cuttings which you cut beginning of July and immediately stick into the ground.

The solitary flowers appear at the junction of the topmost leaves. Each bloom only lasts for a day, but new ones appear repeatedly for about a month. Seed pods appear that are 1 to 2 inches across (3 to 5 cm).

Diseases and problems

Swamp hibiscus is occasionally attacked by the Japanese beetle and by sawfly larvae that leave only the veins of leaves behind, making it look like the skeleton of a leaf. If these pests are problematic, try to find organic solutions that won’t harm beneficial pollinators.

This tall plant is moderately vulnerable to leaf spot, leaf scorch, rust and canker.

• Whitefly, aphids and scale are occasionally spotted, but rarely cause major problems.
• Leaf scorch occurs whenever the soil dries out.

Healthy plants grown in a favorable environment won’t need any staking.

Good to know

Flowers always open between 9 and 11 am. This is the reason why Hibiscus moscheutos is used as a “flower clock” in the New York Botanical gardens.

The oversized exotic-seeming flowers are pollinated by native bees. On the plants, a host of different caterpillars find food and shelter, including a few different types of moths.

Hibiscus coccineus is a relative that has similar blooming. It shares the same growing conditions. Pink forms of Hibiscus moscheutos that don’t have the crimson red center were originally thought to be Hibiscus palustris. Today, these are simply considered a colored version of H. moscheutos.

---