The swamp sunflower (Helianthus angustifolius), also known as the narrow-leaf sunflower, is a member of the Aster family. The genus Helianthus contains approximately 150 diverse species of North American sunflowers, including numerous cultivars and hybrids.
A native to the eastern and southeastern United States, it typically grows in wetter areas, such as along streamsides or pond edges, hence the common name. This plant can be a spectacular addition to the home landscape. It is a great species for a rain garden or other moist naturalized area where it can establish and spread freely.
Read on to learn more about this wonderful wildflower and how you can grow it in your landscape.
Swamp Sunflower Plant Overview
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History
The beautiful Helianthus plant attracts native birds and insects in its natural habitat.
Swamp sunflower is native to the eastern United States, from New York south to Florida and west to Texas. Within its native region, it grows in a diversity of habitats, including fields, open woodlands, and moisture-rich areas alongside ponds and streams.
This plant is an excellent choice to grow along a wetland border. Swamp sunflowers will thrive where many other plants will be difficult to establish because of the constantly wet soil conditions.
This plant is beautiful in its natural habitat. Many native birds and insects are attracted to Helianthus plants. It has also gained the attention of adventurous home gardeners.
Because these plants grow quite tall, they require a larger plot, but this would be a great option if you have the space. Swamp sunflower is hardy in USDA plant zones 5 through 9 and will grow as a perennial within this range.
Helianthus plants are easy to grow from seed, and there will be plenty of options, including the swamp sunflower, for anyone wanting to grow native sunflowers.
There are also plenty of Helianthus cultivars that have been bred to appeal to gardeners. If an 8-foot tall plant is simply too big, you can grow several petite varieties instead.
Cultivation
If you have a larger garden space and are looking for a tall flowering plant to bring late-season color, swamp sunflower may be the wildflower for you. Pollinators also love this plant. Place it in the background of your butterfly garden or pollinator garden or in a naturalized prairie planting.
Swamp sunflower is tall and bold, producing many showy, bright yellow flowers with prominent dark brown centers. Younger plants develop one or two primary stems, while more mature plants develop multiple stems, each lined with numerous thin, alternate leaves.
Each stem is capable of producing many 1.5 to 2-inch wide flowers. Flowers bloom during the summer and fall.
This plant can grow quite large, up to 8 feet tall, so give it plenty of space to grow. It won’t need any special treatment other than periodic thinning and staking to help keep plants upright and growing vigorously.
Swamp sunflowers enjoy similar growing conditions to most other sunflower varieties.
Propagation
If you want to try growing this Helianthus species, seeds are a great way to start. Seeds are inexpensive, readily available, and very easy to grow.
You don’t need any special equipment to start a large sunflower plant from a small seed; just a bit of patience, a sunny plot of land, and access to water. Plants can also sometimes be purchased as young seedlings, and mature multi-stalked plants can be divided and transplanted.
Seed
Avoid burying the seeds too deeply, as they require both light and moisture for germination.
Starting swamp sunflowers or any other Helianthus variety from seed is relatively easy. First, you will need to obtain seeds. An assortment of Helianthus seeds are available commercially, including swamp sunflowers.
Alternatively, if you know someone already growing these flowers, you can collect seeds from mature plants in the late fall. Seeds are typically viable for a couple of years after harvest, but you will have the best germination rates with the freshest seeds.
Sow seeds in the early spring. You can start them indoors, but the preferred method is direct sowing outdoors. Native sunflowers will grow easily when started outdoors, directly sown at the proper depth into your garden plot. In early spring, as soon as the soil can be worked, loosen the top layer of soil.
Lay the seeds every 6 inches and cover them with a very light dusting of soil, no more than ¼ inch. Do not bury them – these seeds need both light and moisture to germinate.
Keep the seeds moist until they sprout, and keep the soil continuously moist throughout their lifecycle. These plants love water!
When seedlings are several inches tall, thin them to one plant every 1 to 2 feet. Remember, they will come back year after year and produce new stems each year, so allow your young plants plenty of room to expand.
Seedlings
Transplanting purchased swamp sunflower plants is an easy way to start growing sunflowers.
If you find swamp sunflower plants from a garden center or specialized plant nursery, they will generally be young seedlings growing in plastic pots. This is a very simple way to get started growing any variety of sunflowers. All you need to do is transplant your purchased plants into your garden.
It’s best to transplant on an overcast day in the spring or fall. In the desired location, dig a hole slightly larger than the pot your plant came in.
Gently remove the plant from the pot and transfer it into the hole. Fill in the remaining gaps with soil, and then give your plant a hearty watering to get it started.
Division
Breaking up larger clusters of perennials through division is a dependable and efficient way to propagate.
Division is a reliable method of breaking up larger clusters of perennials and propagating them quickly and easily. If you have an existing cluster of swamp sunflowers and you are ready to divide them into smaller clusters, this is a relatively simple task.
Dig up part of an existing cluster of sunflowers in the early spring. Plant the divided clump in a new location and give it a good drink of water to get it started. New growth will emerge and fill in as soon as the weather starts to warm.
How to Grow
Swamp sunflowers are easy to grow if you have the correct location. These plants love full sun and plenty of soil moisture. They also need plenty of space because they will grow tall and multiply. If you have the proper conditions, these flowers will thrive as a beautiful addition to your landscape.
Sunlight
Helianthus plants grown in full sun are generally stronger and yield more flowers.
Helianthus loves full sun. After all, Helio means “sun” in Greek, and Anthos means “flower” in Latin. Give these plants at least 6 to 8 hours of direct sunlight daily.
They can tolerate some dappled, partial shade, but plants grown in full sun are likely to be more robust and produce more flowers than those grown in a shadier location.
Water
Swamp sunflowers thrive in water and are not easily overwatered.
True to their name, swamp sunflowers love water. It would be difficult to overwater these plants. Ideally, they would grow best in a location with relatively constant soil moisture. They will tolerate an occasional drought and are well-adapted to an occasional flood.
Soil
These wildflowers tolerate different soil types, including sandy and heavy clay soil.
Swamp sunflowers can be grown in average-quality soil. They are not too picky about soil quality and will tolerate sandy, well-drained soil, or even heavy clay soil, as long as they are exposed to regular soil moisture.
Climate and Temperature
They thrive in temperate climates with hot, humid summers and moderately cold winters.
Swamp sunflowers thrive in temperate climates, in USDA plant hardiness zones 5 through 9. They do well in hot, humid summers and moderately cold winters.
Because these plants are herbaceous perennials in zones 5 through 9, they will die back in the winter but will fully regrow the following year.
Fertilizer
This native plant requires minimal maintenance and doesn’t need extra fertilizers.
A major benefit of landscaping with native plants is that they do not need additional fertilizers. Native plants, such as the swamp sunflower, tend to do just fine with minimal maintenance, just as they do in their natural habitat. Don’t worry about any fertilizer needs for this hardy plant.
Maintenance
If your swamp sunflowers grow tall and begin to droop, consider staking them for support.
Swamp sunflowers can grow rather tall, and if you find your plants flopping over, you may need to stake them to help them stay upright.
The other maintenance you may want to do is some pruning. During mid-summer, before they start blooming, you can use sharp pruners to cut back your plants about halfway. This will encourage them to grow fuller and more densely and may help minimize the need for staking.
Garden Design
Add this species to your garden if you have a sunny naturalized area.
Some landscape designs need tall plants. Taller plants add vertical structure and can help attract a greater diversity of birds and butterflies. Having a variety of different-sized plants in the landscape also creates a more interesting planting assortment to admire.
Tall plants generally look great towards the rear of a planting area. If you have the lowest-growing plants in the foreground, mid-sized plants in the middle, and the tallest plants in the background, you can see them all at once.
If your garden is large, you can create a pathway through the center to easily access the farthest plants.
Swamp sunflowers would be a wonderful addition to a bird-friendly garden or to a butterfly, bee, or pollinator garden. If you have a sunny naturalized area, plant a patch of Helianthus and let them grow wild. You can have a field of native sunflowers!
Companion Plants
Also known as interplanting, companion planting can be used in many ways. Companion plants can be planted together to benefit each other, such as attracting pollinators or repelling pests. Ideal pairs can also be similar plants that thrive in similar conditions.
Like swamp sunflowers, the plants listed below enjoy a location with constant soil moisture and full sun. If you are filling a larger naturalized area, try some of these additional plants as well.
Bushy Bluestem (Andropogon glomeratus)
The bushy bluestem is an ornamental grass thriving in constant soil moisture.
Bushy bluestem is an ornamental grass that grows 2 to 4 feet tall. The stems turn reddish, and the flowers create dense, bushy tufts in late summer. If you have a moist area for gardening, this is one of the few ornamental grasses that thrives in constant soil moisture.
Joe Pye Weed (Eutrochium purpureum)
This popular perennial thrives in moist soils and full sun.
Joe Pye weed is a tall plant, growing up to around 7 or 8 feet tall. It grows in areas with moist soils and full sun but also tolerates partial shade.
Joe Pye Weed is native to central and eastern North America and blooms in late summer and early fall. The pale pink-purple flowers grow in large fluffy-looking clusters and attract butterflies.
Mountain Mint (Pycnanthemum tenuifolium)
The mountain mint blooms continuously from summer until the onset of the first frost.
Mountain mint, or narrow-leaf mountain mint, is native to the central and eastern United States. It can grow 2 to 4 feet tall in stiff, fine-leaved stems.
Flowers have a long bloom time, lasting throughout the summer and often until the first frost. The flowers are favored by many pollinators, and the leaves have a pleasant minty aroma.
Swamp Mallow (Hibiscus moscheutos)
The swamp mallow is a tall perennial shrub that thrives in moist soils.
The swamp mallow, also known as hardy hibiscus or swamp rose mallow, is a tall shrubby perennial. It is native to southern and eastern North America and grows in rich, moist soils.
The flowers bloom in late summer and are very large and showy, in bright shades of pink. The flowers attract butterflies and other pollinators.
Swamp Milkweed (Asclepias incarnata)
The swamp milkweed thrives in moist grassland habitats and along stream margins.
Swamp milkweed is native to the eastern United States, where it grows in moist grassland habitats and steam margins. Not only is this plant very showy with its large pink-purple flower clusters, but it is also a pollinator magnet and a host plant for the Monarch butterfly caterpillar.
Wildlife Value
This is a fantastic plant that supports wildlife.
Swamp sunflower is a wonderful wildlife-friendly plant. Animals and pollinators benefit from this plant and other Helianthus throughout the year. Grow it as part of a butterfly, pollinator, or bird garden.
As a late-season bloomer, swamp sunflower benefits many pollinators. Butterflies and bees frequently visit the flowers. The swamp sunflower is a larval host plant for several butterfly species, including the Silvery Checkerspot butterfly, Gorgone Checkerspot butterfly, Painted Lady butterfly, and Bordered Patch butterfly.
In the fall, the mature seedheads attract birds. You might see goldfinches or indigo buntings perching on the stems to feed on the seeds. Deer generally do not eat this plant.
Pests and Diseases
Most plants are susceptible to at least a few pests and diseases. Fortunately, the swamp sunflower is fairly hardy and tends to grow well, even when it does suffer from minor problems. As a general rule, check on your plants regularly.
Look out for insect pests and changes to the leaves or any other indication that your plant may have a problem. A healthy plant looks fresh and green.
The most likely problem you may encounter is taller plants that bend over. When grown in shaded areas or rich soil, these plants may be especially prone to falling over. Stake them upright so you can see and enjoy the flowers and birds, butterflies, and bees.
Powdery Mildew
This fungal infection thrives in damp, humid areas with limited airflow.
Powdery mildew is a relatively common fungal infection widespread throughout many plant families. It causes a powdery grayish or whitish film to appear on the leaves of a plant. Badly infected plant leaves may turn brown, curl, and die.
Powdery mildew is caused by a fungus that thrives in moist, humid environments with poor air circulation. Sunflowers affected with powdery mildew will generally continue to grow and flower.
Badly infected sections of the plant can be pruned and discarded. If desired, treatment with neem oil or a sulfur-based fungicide after pruning infected leaves can slow down any further spread.
Leaf Spot
A leaf spot infection can cause leaf death and even kill the whole plant.
Leaf spot is another common fungal or bacterial infection. It causes darkened, browned, dead spots to appear on the leaves. It can be unsightly and lead to leaf death; in extreme cases, it can lead to plant death.
Heavily infected portions of the plant should be pruned and destroyed (do not compost diseased plant material). Use a copper or sulfur-based fungicide to treat the rest of the plant to prevent further spread.
You can help improve plant health and resistance by watering at the soil level rather than wetting the leaves and keeping plants well-spaced to improve air circulation. Also, wash your hands and tools after handling infected plants.
Caterpillars
Let the caterpillars eat the sunflower leaves to aid the larval stages of crucial pollinators.
Several caterpillars eat sunflower leaves. Many of these caterpillars will become beautiful butterflies, so if you can, allow the caterpillars to eat the leaves so you can help support the larval forms of these important pollinators.
Frequently Asked Questions
Swamp sunflower is not considered an invasive species but it can grow and spread quickly. If you plant it in ideal conditions, with full sun and moist soil, you will find yourself with a large and healthy patch of swamp sunflowers. They spread by underground stolons and by self-seeding, so you will need to do some active maintenance to control unwanted spread. You can mow around your patch or hand-pull small plants to easily remove them each spring.
As the name implies, swamp sunflower really prefers moist soil. It is much more tolerant of saturated soils than dry soils. It may be drought tolerant for brief periods, but if you have soil that’s generally dry, you would be better off choosing another variety of sunflower, such as the western sunflower (Helianthus occidentalis) which prefers dry to medium moisture soil and is more drought-tolerant than swamp sunflower.
If you start swamp sunflowers from seed in the early spring, you will most likely have a flowering plant by mid to late fall. In the following years, the plants will be better established and they will grow larger and produce more flowers. If you don’t get flowers in the first year, you will certainly see them during the second year.
Final Thoughts
If you enjoy gardening with native plants, have a moist sunny plot of land, and love sunflowers, the swamp sunflower would be a perfect addition to your landscape. The most important thing to remember about this plant is its love of sunlight and moisture.
It can grow tall and spread over time, creating a lush stand of bright yellow flowers that bloom late in the season. Grow it to attract butterflies, bees, birds, and other pollinators. The flowers also make good cut flowers, and the bright yellow, late-season blossoms add beautiful fall color to any landscape.
