Swamp Sunflower Facts, Care & Planting Guide (Helianthus angustifolius)


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how to grow swamp sunflower
Photo by Eric Hunt / CC BY-SA

Also known as narrow-leaf sunflower, swamp sunflower (Helianthus angustifolius) is a member of the aster family.  The Helianthus genus also contains a variety of other sunflower species.  Unlike many other sunflowers that must be replanted year to year, swamp sunflower is a perennial and will persist in your garden for multiple years. 

Swamp sunflower is native to the eastern and southern-central United States.  Although it is not technically invasive outside of these areas, swamp sunflower enthusiastically grows and reseeds, and can spread easily through underground rhizomes.  In the wild, they can be found growing in floodplains, bogs, swamps, and marginally along the damp edges of rivers, ponds, and the like. 

Swamp sunflower quickly grows to 5-8 feet tall, producing clusters of flowers.  As a member of the aster family, this plant produces ray and disc blooms with structure similar to daisies, chamomile, and cosmos.  The blossoms are 2-3 inches across, consisting of 10-15 bright yellow petals and reddish-brown centers.  After flowers are done blooming, they leave behind seed pods.  Swamp sunflower’s other common name, narrow-leaf sunflower, refers to its long, narrow leaves. 

Facts, Benefits & Uses of Swamp Sunflower

silvery checkerspot butterfly on sunflower
The swamp sunflower is an important host plant for the silvery checkerspot butterfly. Photo by Judy Gallagher / CC BY

Swamp sunflower attracts a wide variety of pollinators, including bees and butterflies.  The plant serves as a host for the caterpillars of the silvery checkerspot butterfly, among others.  Adult butterflies lay hundreds of eggs on the undersides of swamp sunflower leaves.  Once hatched, the caterpillars skeletonize the leaf, meaning that they eat all of the leaf except for its veins.  Swamp sunflower seeds also attract animals such as songbirds, quail, and deer, which utilize the seeds as a nutrient and fat-rich food source in late fall and winter.

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Swamp Sunflower Fact Sheet:
PLANT TYPE
Herbaceous Perennial
HARDINESS ZONES
USDA 5 – 9
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
Yellow
BLOOM PERIOD
August – October (Autumn)
MAXIMUM GROWTH
Height 150-240cm (59-94in)
PLANTING DEPTH
Place seeds on soil surface
WATER QUALITY
pH 5.0 – 7.5

Swamp Sunflower Growth, Hardiness & Climate

swamp sunflower growing in swamp
Swamp sunflower, as its name implies, is able to grow in heavily saturated areas like swamps. Photo by mogollon_1 / CC BY-SA 2.0

As suggested by its name, swamp sunflower grows best in thoroughly moist soil.  This is generally a hardy, easy to cultivate plant when grown in the proper conditions.  Swamp sunflower should be planted in full to partial sun, and can do well in poorly drained soil, making it a great option for pond margins or other wet areas.  This plant can also adapt to drier soils, although it will likely not grow as large or produce as many blooms. 

Swamp sunflower spreads via rhizomes, which allow it to spread 3 to 5 feet wide per plant.  A swamp sunflower plant will grow to reach 5-8 feet in height.  This plant’s significant height and spread is something to take into consideration when choosing plants for smaller gardens.

Swamp sunflower typically flowers in late summer and early autumn, when many other plants are finished blooming for the season.  These late-blooming flowers make swamp sunflower a desirable option for extending the flowering season in your garden.  This plant survives best in hardiness zones 5-9.  It’s also salt-tolerant, and so is a good option for a coastal garden. 


How to Plant Swamp Sunflower In Ponds

swamp sunflower plant care
Swamp sunflower can spread via rhizomes, and can be easily divided and replanted to control spread. Photo by Eleanor / CC BY-NC 2.0

To grow swamp sunflower from seeds, gently press seeds into soil in the spring once any risk of frost has passed.  Be sure that seedlings have access to plentiful sunlight and water.  Mature plants can also be easily dug up and divided in early spring if you would like to transplant to different areas or limit the size of your plant.  Swamp sunflower will grow tallest and widest in wet soil but can also tolerate drier conditions.  However, it will not grow well or flower if not provided with adequate water. 


How to Care For Swamp Sunflower

how to care for swamp sunflower Helianthus angustifolius
Swamp sunflower grows best when provided with ample sunlight and saturated or damp soils. Photo by bobistraveling / CC BY-SA 2.0

Swamp sunflower thrives best when grown in full to partial sun and moist soil.  In general, swamp sunflower is a hardy plant and, once established, needs little maintenance aside from plenty of water.  Seedlings should be kept moist.  While mature plants do best with damp soil, they also tolerate periods of dryness and flooding. 

Swamp sunflower plants grow well on the margins of a pond, as this location provides the plant with ample water.  When your plant has grown tall and is heavy with blooms, it may require staking to prevent stems from bending or snapping.  You can periodically thin out swamp sunflower if needed.  If you’re concerned with the height of H. angustifolius, snipping the flower heads early in their development can help reduce vertical growth and result in more flowers.  In nature, deer often perform this task for the plant!


How to Winter Swamp Sunflower

H. angustifolius flowers and stems will die back in the winter but will grow back from roots in the spring. This plant is winter hardy in zones 5-9, and doesn’t require any special care to survive the winter in these areas. Outside of these areas, you can easily harvest any seeds in the fall and plant them the following spring, or simply dig up any plants and transfer them indoors for the winter.


Is Swamp Sunflower Toxic, Poisonous or Invasive?

swamp sunflower toxicity edible
Swamp sunflower is not known to be toxic, and in nature is readily eaten by deer and birds.

Outside of its native areas in North America, swamp sunflower can certainly become invasive.  Swamp sunflower grows quickly and easily from seed, and also spreads through underground rhizomes.  Methods to limit its growth include removing blooms before they go to seed and pulling some roots and rhizomes from the ground.  This plant is hardy and should tolerate such measures without problems. 

Another factor that makes swamp sunflower especially persistent is that it is a perennial, living for multiple years.  Gardeners outside of swamp sunflower’s native zones in North America might consider growing an annual, less invasive variety of sunflower, such as common sunflower (Helianthus annuus).  However, most other sunflower species will not be as water tolerant as swamp sunflower is, and therefore may not be good options for a pond garden. 

Swamp sunflower is not toxic to dogs, cats, or horses.  This plant is also not toxic to humans and is commonly eaten by a variety of birds and insects.  Swamp sunflower is not thought to be toxic to fish, and it does not grow entirely underwater where fish would have easy access.


Is Swamp Sunflower Edible? Will Fish Eat it?

Swamp sunflower seeds are edible, although they are not as large and easy to eat as those of the common sunflower, helianthus annuus.  A close relative of swamp sunflower, the Jerusalem artichoke (or sunchoke), produces edible tubers which are widely cultivated.  However, swamp sunflower is not commonly eaten by humans.  Your fish are unlikely to show much interest in eating swamp sunflower, but it should not cause any problems if they happen to get a bite.


Where to Buy Swamp Sunflower & Seeds? (UK & US)

Swamp sunflower seeds can easily be found in North America from a plant nursery or online outlet.  In other locations, you’ll likely have to order swamp sunflower seeds online.  However, please proceed cautiously with this plant in areas where it is non-native, as swamp sunflower spreads easily! As always, please remember to try to purchase and grow plants for your pond or garden that are native to your area.

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