Swamp sunflower (Helianthus angustifolius) is a plant species that is a member of the Aster family. The swamp sunflower or Narrow Leaf Sunflower, is a yellow perennial flower. It grows well in damp gardens and tolerates the salt of coastal areas. It spreads in small, slow-growing clumps.
I. Appearance and Characteristics
Helianthus angustifolius is a species of sunflower known by the common name narrowleaf sunflower or swamp sunflower. It is native to the south-central and eastern United States, found in all the coastal states from Texas to Long Island, and inland as far as Missouri. It is typically found in the coastal plain habitat (both the Atlantic and Gulf), particularly in wet areas.
Helianthus angustifolius is often cultivated for its bright, showy yellow flowers. Leaves are long and narrow, up to 15 cm (6 inches) long. It is a perennial herb sometimes as much as 150 cm (5 feet) tall. One plant can produce 3-16 flower heads, each with 10-20 ray florets surrounding at least 75 disc florets.
II. How to Grow and Care
Sunlight
The seedlings, leaves, and flower heads of sunflowers all exhibit very strong phototropism. Sufficient sunlight will make the seedlings grow strongly and healthily. During the middle period of their growth stage, sufficient sunlight can promote the growth of stems and leaves and the differentiation of flower buds. If sunflowers receive sufficient sunlight during their entire growth period, the stems and leaves grow healthily and the flowers are vivid and bright. However, if there is continuous rain or they are grown for a long time in a partially shady spot they may grow poorly and become weak. The stems will not be straight, the leaves will be soft and droop in yellow green, and the flower head will be small and irregular.
Temperature
Sunflowers native in North America, where it is cold in winter and hot in summer, have a significant annual variation in temperature. Sunflowers likes a warm environment. The suitable temperature for growth is 18 to 30 ℃ and they can grow normally as long as the temperature is not lower than 10 ℃. Within a suitable temperature range, the higher the temperature is, the faster the Sunflowers grow.
In different stages of growth, Sunflowers require different amounts of water, and in general, they are drought-resistant. The soil shall not be too moist and no water logging is important. From the budding period to the flowering period, stable water supply shall be ensured for good blooming.
Watering
Sunflowers have different water requirements at different stages of growth. The soil must be moist during sowing and transplanting. The plants need sufficient water, especially during the seedling stage. After that, the soil should be kept moist but not excessively wet. Some drought is beneficial for root growth and to develop a plant’s drought tolerance. In the summer, when the temperature increases and water evaporates more rapidly, the amount of water supplied can be increased as necessary to prevent wilting, which can affect the growth of the plants.
The time from the emergence of flower buds to blooming is the peak period of water demand in sunflowers. During this time, there should not be a lack of water; if the soil becomes too dry, it should be watered. When sunflowers are grown in pots, the plants are often large while the flower pots are small, and there may be just a little soil and insufficient water. Therefore, timely watering is required during the growth period; otherwise, the leaves tend to loss water and wither. The soil should not be too wet, however, otherwise the leaves at the base of the plant tend to turn yellow.
Soil
Sunflowers can grow well in all types of soil. However, the soil they most prefer is sandy loam or loamy soil, with a pH of between 5.8 and 6.5. Good soil drainage is crucial for the growth of sunflowers. If sunflowers are planted in the garden, it is recommended that loose and fertile loam is used, which can be mixed with decomposed compost as a base fertilizer. Quick-acting fertilizer can also be added. Soil should be dug over prior to fertilization and sowing to improve soil structure and drainage.
If sunflowers are grown in pots, their soil should be made up of peat, vermiculite, and sand in the ratio 2: 1: 1; organic fertilizers can be mixed in at the same time. Please note that sunflowers should not be continuously planted in the same soil or in soil where other plants of the same family have been planted, otherwise they will grow poorly. It is recommended that the soil is replaced once a year, or that sunflowers are grown in a different area.
Fertilizing
When sunflowers are grown in pots, liquid fertilizer or compound fertilizer should be applied once every 7 to 10 days. During the growth of seedlings, nitrogen fertilizer should be applied to promote the luxuriant growth of stems and leaves. When budding begins, more phosphate-potassium fertilizer should be applied, which will provide sufficient nutrients to promote robust growth of the buds and facilitate blooming.
If sunflowers are planted in the garden, no fertilizer is required if the soil is already fertile. However, if the soil is relatively poor, nitrogen fertilizer should be applied during the early stages of growth and phosphorus and potassium fertilizers should be applied during the late stages, similar to that carried out for potted plants. They can be fertilized once every 20 days during the growth period, with an additional two or three applications of thin phosphate-potassium fertilizer provided before blooming.
Planting Instructions
Sunflowers are generally sown in late winter or spring and will bloom 60 to 70 days after sowing. The seeds should be sown directly into the soil, with spacing between the seeds of at least 12 cm. After sowing, a 2 cm layer of fine soil should be used to cover the seeds. Then, the seeds should be watered before being covered with a layer of mulch.
If sunflowers are sown in seed trays, deep seed trays should be used. First, place the compost into the seed tray, thoroughly water it, and wait for the excess water to drain before sowing. Sow each seed in a hole, cover it with a thin layer of soil, place the tray in a shady place, and wait for the young seedlings to appear.
Once the seedlings appear, ventilate them well, reduce the humidity and temperature, and gradually expose the seedlings to sunlight. Two weeks after sowing, the seedlings will grow to about 5 cm. At this time, the seedlings can be transplanted into a 10 cm pot and cared for until planting out. The optimum soil temperature for planting sunflowers is 15 ℃.
Pruning
To ensure the robust growth of the main stem, the lateral buds of sunflowers should be removed so as not to distribute nutrients too widely and affect the growth of flowers on the main stem. If planted in a border, the top bud of the main stem can be picked off, so that branching occurs to give 4-5 blooms and the plant remains quite short and bushy. For sunflowers planted to provide cut flowers, the apical bud should be removed to facilitate the growth of lateral stems. After such treatment, several stems will be produced, and 7-10 flowers can be harvested from one plant. For sunflowers grown in pots, it is recommended to keep the primary stem and remove the lateral buds, since in this case it is better to have just one flower.
Propagation
Sunflowers are usually propagated by sowing seeds. It is a cross-pollinated plant that can be naturally pollinated by insects and bees, although artificial pollination can also be carried out when sunflowers are in bloom, which can improve the seed setting rate and produce more seeds.
Pests and Diseases
Happily, this native perennial does not incur as many pests and diseases as its H. annuum relatives prized for their seeds.
The sunflower midges that plague the large seed heads won’t strike the more modest blooms, for example.
Deer and rabbits may munch on the leaves, but only if they don’t have more appealing options in the spring and summer garden. And since the seeds are smaller and less plentiful, squirrels won’t usually strike either.
As for insect pests, some caterpillars and beetles might gnaw on the leaves, but they won’t keep the plants from blooming later.
If you like, you can take measures to spray the foliage, but I prefer to let the plants grow on since insect pests don’t do too much damage, and various insecticides can hurt the pollinators that depend on plants like swamp sunflowers.
There is a chance these moisture-loving plants will suffer diseases including powdery mildew, rust, or fungal leaf spots.
Here, too, the damage is ordinarily minor, and the plants can thrive without intervention. If the appearance bothers you though, you may want to try an organic fungicide such as copper.
III. Uses and Benefits
While they don’t yield mass quantities of seed to roast or save for the birds like annual sunflowers, H. angustifolius is highly desirable in many garden situations.
First, they’re ideal for a swampy spot, like the dirt at the bottom of a downspout or an area near a pond.
They’re lovely in native plantings, where their appeal to pollinators will also help the entire ecosystem thrive.
They also look good at the back of borders, especially in a fall-blooming perennial garden, where they’ll provide color long after summer annuals have stopped flowering.
And don’t forget that they are a good option for coastal gardens since they can sustain some salt air.
Last but not least, they’re a great choice for the flower gardener who doesn’t want to fuss.
Not only are they easy to care for, they readily self-seed, and the rhizomes will typically resprout each year as well.
IV. Harvesting and Storage
For sunflowers planted to be used for cut flowers, they can be harvested when the outermost ligulate flowers bloom. It is best to harvest them in the early morning when the temperature is low; they should not be harvested at midday or in the afternoon, when the temperature is high. Gardening scissors should be used to cut the inflorescences obliquely at the bottom of the stem; this can increase the area for water absorption.
The cut inflorescences should be placed in a container of clean water as soon as possible to avoid water loss. If the flower cannot be placed into water immediately, the bottom of the stem should be cut again before it is placed in water to ensure sufficient water absorption. The vase life of sunflowers is 6 to 8 days in the summer and 10 to 15 days in the winter.
Find Where to Buy the Best Swamp Sunflower (Helianthus angustifolius)
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