Helianthus giganteus, Tall Sunflower

Helianthus giganteus is Floyd County’s tallest native sunflower, reaching up to 12′ tall and 4-6′ wide in a few years. Tall Sunflower sports branching clusters of 3″ diameter yellow flowers above stiff branching stems and lance-shaped leaves.

Cultivation

This plant’s tall size and vigorous growth make it poorly suited to small gardens and neatly contained landscapes. However, it can produce a profusion of blooms and fill in large empty spaces so beautifully that it’s worth studying how to make the most of this native flowering perennial. Although it typically grows wild along river and stream banks, or in low-lying ditches, it can grow in drier conditions. In fact, the University of Arkansas’ plant of the week article shares some excellent suggestions about how to cultivate these plants using this inherent adaptability. An excerpt: “…don’t encourage rapid growth by planting in rich sites or by fertilizing. Try to locate the plants in a sunny, wind-whipped area where the exposed conditions will produce stouter stems.”  (Plant of the Week: Helianthus giganteus, Giant Sunflower, University of Arkansas Cooperative Extension Service). The article goes on to recommend vigorous pruning to restrain its height where desired, including mowing the plants to the ground in early June, after which they should grow back up and bloom in the fall, topping out at the much more manageable height of 5′.

Ecology

The Helianthus genus tends to be a strong contributor to ecosystems, providing nectar, pollen, bird seed, and hosting many Lepidoptera (butterfly and moth) species which in turn support birds and other predators. (See NWF’s keystone species list based on the work of Dr. Doug Tallamy). NWF’s Native Plant Finder has records of 66 species of Lepidoptera beginning their lives as caterpillars on the six species of Helianthus found in the Floyd County area. This includes the Giant Leopard Moth (Hypercompe scribonia) (not be confused with the Spotted Lantern Fly).

PLANT FACTS


Scientific Name

Helianthus giganteus

Other names: Giant Sunflower, Helianthus alienus, Helianthus borealis, Helianthus giganteus ssp. alienus, Helianthus giganteus var. subtuberosus, Helianthus nuttallii var. subtuberosus, Helianthus subtuberosus, Helianthus validus

Family: Asteraceae (asters).

Native Status

Native to Floyd County

Native Range Map (Virginia Counties) for Helianthus giganteus

Source: Digital Atlas of the Virginia Flora

Helianthus giganteus BONAP map 2014

Source: BONAP 2014

 

Other Floyd County native Helianthus: H. divaricatus, H. decapetalus, H. strumosus.

Culture Notes

Height: 10-12 ft, Spacing guide: 3-6'. Bloom Color: Yellow. Bloom Time: Late Summer/Early Fall (Jul-Sep). Light: Full sun to part shade. Moisture: Medium to moist (mesic to subhydric) conditions. Soils: Moist sandy, loam, or clay, mildly acidic to mildly alkaline soils.

Habitat

USDA Zones: 3-9. National Wetland Status Indicator: FACW. C-Value: 6. Successional Role: Subclimax, stable.

Virginia Ecology

Virginia Habitat: "Bogs, wet fields, meadows, ditches, and low roadsides; rarely in freshwater tidal marshes. Frequent in the Piedmont; infrequent in the mountains and Coastal Plain." (The Flora, 2023). Virginia Natural Communities: None specified

Ecosystem Services

*Of Special Value to Native Bees, Bird Food

Wildlife Supported: Bees and flies collect the nectar, birds eat the seeds, 66 species of Lepidoptera (butterflies and moths) hosted by the six species of Helianthus found in the Floyd County area.

Propagation

Propagate from seed, stem cuttings, or division in early spring. Seed Collection notes from Wildflower.org: "Nutlets usually mature 2-3 weeks after flowering. To beat finches to the seeds, secure a small bag around seeds heads after the flowers fade. Air-dry collected seed heads, separate nutlets from chaff, and store in sealed, refrigerated containers." Best germination from refrigerated seeds stored overwinter, then cold moist stratified for 30 days prior to planting. Seed Germination: C30 - 30 days cold moist stratification required

Where to Buy

Ernst Seeds, Prairie Moon Nursery, Etsy