Swamp Rose Mallow

In June of 2014, three tall plants with bright pink blooms emerged in my pasture. At roughly seven feet they towered above the thick briers and Japanese honeysuckle that made the area nearly inaccessible. For a gardener who had struggled against invasive plant growth, it was unbelievable that anything so exquisite could compete with strangling vines and thorny brambles. The flowers were 4 to 6 inches in width. They bloomed apically, at the very top of the plant. Each bloom had five wide petals waiving like the hand of a friendly neighbor. A mad dash to find my well-worn copy of National Audubon Society Field Guide to North American Wildflowers revealed that this plant was swamp rose mallow. The botanical name is Hibiscus moscheutos, or Hibiscus palustris, which is generally regarded as a subspecies of H. moscheutos (Mosquin, 2015). That was the beginning of my effort to expand the habitat of the native plant that had established a foothold here.

Swamp rose mallow is a member of the family of plants called Malvaceae, commonly called mallows. The mallows are one of the most well-known families of plants The more economically important mallows are cotton, cocoa, okra and kola nut (the original cola flavor). Other beloved members of this family are hibiscus, hollyhocks and the rose of Sharon tree (Williams, 2018). Gardeners who have grown okra will recognize similarities between okra and swamp rose mallow. Both plants become woody as the season progresses. Both die down as the weather gets cold, leaving a brittle, dead stalk. Swamp rose mallow’s leaves are thick, coarse and scratchy like the okra plant’s. Unlike okra’s palmate leaf, swamp rose mallow leaves are ovate and deeply serrated. They resemble those of another member of the mallow family, the rose of Sharon, which is a popular yard tree.

A Plant With A History

Mid-1700s naturalist John Bartram collected seeds from mallows including hibiscus moscheutos, and provided American and European growers with seeds. His Philadelphia botanical collection is the oldest in the United States. Bartram and his brother, William Bartram, traveled widely, researching herbs and trees of eastern North America. George Washington and Thomas Jefferson both visited the Bartrams’ plant collection and obtained seed from their garden (Fry et al., 2002). In his Notes on the State of Virginia, Thomas Jefferson writes, “I will sketch out those (plants) which would principally attract notice... I shall confine myself too to native plants.” He goes on to include Hibiscus moschentos (alt of H. moscheutos) in his list of useful plants (Jefferson, 1785). Although there is no documentation proving that Washington or Jefferson grew this exact species of hibiscus, it has long been grown in the gardens of both Mt. Vernon and Monticello. Based on seasonal availability, seeds can be bought through the Mt. Vernon and Monticello websites. Gardeners who grow swamp rose mallow join the ranks of early Americans who appreciated this plant.

What Makes Swamp Rose Mallow a Great Native Plant

Over the last couple of decades, gardeners have recognized the value of working with native plants. They are less susceptible to pests and diseases, and they don’t need as much care. They support the native ecology. Swamp rose mallow is one of a few plants that act as host to the rose-mallow bee (Ptilothrix bombiformis), a specialist bee that feeds on and mates in hibiscus blooms (Simpson).

Different populations of rose mallow, also called dinner plate hibiscus, bloom in different colors. Most botanists still consider them to be the same species. Flowers range in color from cream to light pink to deep pink. A mix of seed bought from different locales could yield an assortment of bloom shades.

Tall, rugged and spectacular plants such as swamp rose mallow allow landowners to turn previously inhospitable areas of property into a source of pride. Remove plants that shade out other plants. Inhibit the return of invasive plants by replacing them with native plants.

How to Plant

One swamp rose mallow plant is beautiful, but a colony of the plants is spectacular. To establish the plants, sow seed or dig up and divide the crown (roots) of a mature plant. Early spring and late fall are the best times to sow seed. The seed germinates readily as the weather gets warmer.

It is usually easier to collect seed than to dig up a section of roots. The flowers dry into woody, star-like pods, which remain at the top of the plant. Their height makes them easier to spot, even if it makes them harder to reach. The seeds are brownish gray and nearly spherical. They look like okra seeds, but much smaller. Don’t plant the seeds too deep. Just gently pat them into the ground. They only need about an eighth of an inch of soil over them.

The planting site must stay reliably moist. Older swamp rose mallow can survive brief periods of dryness, but younger plants should be watered frequently. Give the plants an advantage by digging a shallow bowl-shaped hollow in the ground for the plant. Make it 12 to 18 inches in diameter and 8 or 10 inches deep. This will create a low spot to hold water, like a tiny pond for each plant. Place the seed or young plant in the bottom of this little hollow.

Where to Plant

Swamp rose mallow grows best in USDA zones 4 through 9. It likes full sun, but tolerates some shade. It is found in the wild from the eastern United States west to Texas and Utah. It grows in southeastern areas of Canada, but it isn’t as common there. Canada has given the plant “Special concern status” (COSEWIC 2004).

Edges of ponds and low, moist spots are places where swamp rose mallow thrives. Swamp rose mallow is a tough plant that adapts as water levels rise and fall. It doesn’t do well if it is completely submerged or if its soil gets very dry. Grow this mallow beside an ornamental pond, on the bank of a farm pond, or along a gray water drain.

It’s height makes it a good candidate for a border planting. It can line the border of a garden like a hedge. It could be grown in a container, but it would have to be a large one. Based on a root spread of 36 inches, a plant would need at least a five gallon container. Remember, however, that this plant will perform better in conditions that mimic the wild.

Good Plants to Combine

Swamp rose mallow will grow well alongside sedges, rushes, reeds and cattails. All of these plants thrive in moist conditions. Seek out these marginal plants when planting seed; they’ll make good neighbors.

Seasonal Care

The winter months are a great time to scout out a spot for planting. The weeds have died down and aren’t in leaf, so cutting back vegetation is easier. With less vegetation, it is also easier to see the contour of the land. Look for the low spots. Plant seed while the weather is still cool: from winter into early spring.

Gardeners who want to start plants in pots will place them in the ground in spring. The timing is tricky. A hard freeze can kill the plants, but placing them too late can leave the plant stunted. Protect the little plants with plastic drop cloths or plastic bottles. Cut the bottom out of an empty milk jug or clear juice bottle and place it over the plant for protection.

The plants don’t necessarily need fertilizer. Growers who want to fertilize can choose from an assortment of products labeled “hibiscus food”. Natural byproducts work well. Growers who keep an ornamental fish pond can simply water the mallow plants with sludge containing fish waste. Swamp rose mallow is a very low maintenance plant. Leaf blight or rust can show up on these plants, but don’t normally pose a serious threat. It is not generally necessary to apply insecticide, but Japanese beetles can damage the plants.

Seed pods form in fall. Collect the seed to save, plant or share with another gardener. The dormant plants leave a circular crown of dead wood. It is hollow and lighter in color than much of the surrounding organic material. If other vegetation has encroached on the mallow during the growth season, tie a plastic ribbon loosely around the mallow’s old wood. This makes it easier to find and clean up around the mallow.

On a Personal Note

I plan to relocate in about a year and a half. I only have two more growing seasons to nurture these mallow plants. I hope the next owner of the land will respect and appreciate them. I plan to collect as much seed as possible to take to my new home 300 miles away. Leaving the plants behind will be difficult, but a new home will be a place to continue the story of swamp rose mallow.

References:

Niering, William, Olmstead, Nancy, Rayfield, Susan, Nehring, Carol, National Audubon Society Field Guide to North American Wildflowers (Alfred A. Knopf, New York 1996) pp. 626-627

Mosquin, Daniel, Bonnemaison, Tamara, “Hibiscus Moscheutos Subsp. Palustris,” (The University of British Colombia, June 15, 2015) https://botanyphoto.botanicalgarden.ubc.ca/2015/06/hibiscus-moscheutos-palustris/ Hibiscus moscheutos subsp. palustris | Botany Photo of the Day (ubc.ca)

Williams, Marc., “Plant Families” Botany Every Day, May 2018 http://www.botanyeveryday.com/plant-families/malvaceae Plant Families | Botany Every Day

Fry, Joel T. et al, “Historic American Landscapes Survey; John Bartram House and Garden,” (National Park Service Project 2002) pp. 52-55 https://www.nps.gov/hdp/samples/HALS/bartram/HALS_PA-1_Hist.pdf Historic Bartram's Garden - HALS Report (nps.gov)

Jefferson, Thomas, Notes on the State of Virginia, (1785) p.49 www.thefederalistpapers.org/ wp-content/uploads/2012/12/Thomas-Jefferson-Notes-On-The-State-Of-Virginia.pdf Thomas-Jefferson-Notes-On-The-State-Of-Virginia.pdf (thefederalistpapers.org)

Simpson, Melissa, “Rose-Mallow Bee (Ptilothrix bombiformis)” (U.S. Forest Service) www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/rosemallowbee Rose- mallow Bee (Ptilothrix bombiformis) (fs.fed.us)

COSEWIC (Committee on the Status of Endangered Wildlife in Canada) “Assessment and Update Status Report on the Swamp Rose-mallow Hibiscus moscheutos in Canada” (2004) Swamp Rose-mallow (Hibiscus moscheutos) (publications.gc.ca) http://publications.gc.ca/collections/Collection/CW69-14-417-2005E.pdf