The late-blooming swamp sunflower, Helianthus augustifolius, stages a brilliant debut as an auspicious autumnal golden girl from September through November. Standing from 6-10 feet in height the perennial composite displays a profusion of daisy-like 3 inch flowerheads with 15-20 golden ray florets radiating from a center of dark purple disk florets. The coarse textured green leaves are 3-6 inches long but only half an inch wide. The narrow leaves are an easy distinguishing characteristic of this sunflower and one that coined the common name narrow-leaf sunflower. Leaf petioles are purple.
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Sunflowers are native to the Americas. Swamp sunflower, native to the eastern and south central US, grows wild in roadside ditches, swamps, wet pine forests, coastal salt marshes, and along fence boundaries in USDA hardiness zones 6-9.
In the home garden swamp sunflowers require full sun. As their name suggests they prefer moist footing. If grown in dry soil, they need additional irrigation. They thrive in a variety of soil types and tolerate a pH range from 4-7. As garden flowers, they prosper with compost amended soil and fertilizer.
The towering herbaceous stems with top-heavy bloom clusters may need staking. Anchor supports in early spring before the plants shoot skyward.
Gardeners prune tips back in early June to increase branching and flowering.
Gardeners propagate swamp sunflower by direct sowing of seed in spring, division in spring or fall, or root basal cuttings in spring. Plants are spaced 18-24 inches apart due to their mature spread of 3-6 feet.
Generally swamp sunflowers are pest and disease free. However their leaves are susceptible to downy and powdery mildew and to damage from beetles, caterpillars, cut worms, and spittle bugs. The plant is deer resistant.
The swamp sunflower is ideal as a solo specimen or in mass plantings. The golden flowerheads show well against an evergreen background. When swamp sunflowers are used in mixed perennial borders, three late-blooming complementary companions to site them with are the New England aster, Symphyotrichum novae-angeliae, American aster, S.oblongifolium, and seashore mallow, Kosteletzkya virginica.
The perennial is included in rain gardens, wildflower meadows, pollinator gardens, bog gardens, and native wetland plantings. Coastal gardeners appreciate its salt tolerance.
The radiant flowers attract native bees and butterflies. When the plant dies to the ground after the first hard freeze, bird fanciers leave the dry flowerheads on the stalk to provide seeds for birds in winter. In early spring stems can be cut to 6 inches from the ground.
Hybridizers have introduced compact swamp sunflower cultivars with maximum florescence.
Swamp sunflower was selected as one of the top ten native plants for the southeast by the National Wildlife Federation. Consider placing this great golden exclamation point plant at the end of a sizzling summer.
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